Extendable cable

Abstract

Provided is an extendable cable that has high durability and is provided with a curl cord that requires reduced tension for extension.　This extendable cable 1 comprises: a curl cord 2 having a curl portion 2a in which a cable 21 is wound in a spiral shape, and a gap S between adjacent turns of the spiral shape in a natural length; and a regulation member 3 disposed along an axial direction A of the curl portion 2a. The regulation member 3 is less flexible than the curl cord 2 in a direction crossing the axial direction A, and is extendable and contractible along the axial direction A.

Description

Elastic cable

[0001] The present disclosure relates to a stretch cable.

[0002] In various devices, such as automobiles, electrical connections are sometimes made between components whose positions or postures can be changed relative to one another using cables. In such cases, the cables must be able to follow the movement of the components. For example, automobile seats capable of various movements, such as sliding over long distances, rotating, and lifting, are becoming practical so that the interior space of the vehicle can be freely changed. Meanwhile, automobile seats may also be equipped with various sensors for detecting whether the occupant is seated, whether the seat belt is fastened, and the driver's health condition, as well as devices with various functions, such as heaters, anti-drowsiness devices, and massage devices. When sensors and various devices are installed in a movable seat, the cables used to power and control these sensors and devices must be able to follow the movement of the seat. As a mechanism for enabling the cables to follow the movement of components, such as a seat, a holding portion may be provided that can bend the cable into a U-shape or reel it in to hold it in place. When the cable path is short in accordance with the movement of the component to which the cable is connected, the retaining portion holds the excess length of the cable, whereas when the cable path is long, the cable is unwound from the retaining portion.

[0003] As automobile seats are equipped with a variety of functions, the number of sensors and devices required to realize those functions increases, reducing the space available for cable placement. Meanwhile, the number of electric wires supplying power and controlling those sensors and devices increases, leading to cables with more cores, larger diameters, and more wires. This means that cables need to be placed at high density in a limited space. However, if U-shaped or retractable holding units are provided on the cables, the space required for placement of those holding units makes it difficult to accommodate such high-density cable placement. The increased weight and cost of the cables and holding units also poses problems.

[0004] Therefore, the use of curl cords has been considered as a cable that can follow the movement of members such as seats without significantly increasing space, weight, and cost. A curl cord is a cable that is wound in a spiral shape and has elasticity. For example, Patent Documents 1 and 2 listed below disclose curl cords.

[0005] JP 2012-243399 A JP 2017-182951 A

[0006] As a space-saving, flexible cable, curl cords are suitable for electrical connections between moving components. However, they have not yet been widely used for electrical connections between components inside automobiles, such as seats. One reason for this is their low durability. Specifically, when a curl cord is repeatedly stretched and contracted, stress relaxation in the coating material can reduce the stretchability of the curl cord, making it unable to return to its original natural length from the stretched state. One possible method for maintaining high stretchability of a curl cord even after repeated stretching and contraction is to enhance the springiness of the curl cord by improving the materials that make up the curl cord. For example, in Patent Document 1, a steel wire that has been plastically deformed into a spiral shape is integrated into the sheath of the cord body. Furthermore, in Patent Document 2, a cross-linked polymer is used for the insulating coating that makes up the curl cord.

[0007] Increasing the springiness of a curl cord is effective in increasing the durability of the curl cord. However, as the springiness of a curl cord increases, the force required to stretch the curl cord increases. This can cause problems or inconvenience in the movement of the component to which the curl cord is connected. For example, when manually operating a car seat, it is desirable to keep the operating load low. However, if the springiness of a curl cord connected to the seat increases, a large operating load will be required. It is desirable for a curl cord to have durability that allows it to maintain high stretchability even when repeatedly stretched and contracted, while also minimizing the tension required for stretching.

[0008] In view of the above, an object of the present invention is to provide an expandable cable having a curl cord that has high durability and requires a small amount of tension for expansion.

[0009] The expandable cable of the present disclosure has a curled portion in which the cable is wound in a spiral shape, a curled cord having gaps between adjacent turns of the spiral shape at its natural length, and a regulating member arranged along the axial direction of the curled portion, wherein the regulating member is less likely to bend than the curled cord in a direction intersecting the axial direction and is expandable along the axial direction.

[0010] The elastic cable of the present disclosure is an elastic cable that has high durability and includes a curl cord that requires a small amount of tension for extension.

[0011] Fig. 1 is a perspective view showing an expansion cable according to one embodiment of the present disclosure in a natural state. Fig. 2 is a perspective view showing the expansion cable in an extended state. Fig. 3 is a perspective view showing the expansion cable in a compressed state. Figs. 4A and 4B are diagrams illustrating the relationship between the displacement and load of a curl cord. Fig. 4A shows a curl cord with no gaps between turns, and Fig. 4B shows a curl cord with gaps between turns.

[0012] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. An expansion cable according to an embodiment of the present disclosure has the following configuration.

[0013] [1] An expandable cable according to an embodiment of the present disclosure includes a curled portion in which the cable is wound in a spiral shape, a curled cord having gaps between adjacent turns of the spiral shape at its natural length, and a regulating member arranged along the axial direction of the curled portion, wherein the regulating member is less likely to bend than the curled cord in a direction intersecting the axial direction and is expandable along the axial direction.

[0014] In the curled portion of the curl cord constituting the expandable cable, gaps are provided between the spiral turns. The presence of these gaps allows the curl cord to displace not only in the direction of extension from its natural length but also in the direction of compression. In other words, the curl cord can be displaced in both the direction of extension and the direction of compression. Therefore, compared to conventional curl cords that do not have gaps between the turns and can only displace in the direction of extension, the amount of displacement from its natural length required to achieve the same displacement can be reduced. As a result, the load applied to the cable's constituent materials, including the covering material, as the curl cord expands and contracts is reduced, thereby increasing the durability of the curl cord. Furthermore, the tension required to apply to the curl cord to achieve a predetermined displacement can be reduced.

[0015] The presence of gaps between the spiral turns of the curl cord makes the curl cord more flexible than when there are no gaps. However, in the above-mentioned expandable cable, the provision of a restricting member along with the curl cord prevents the curl cord from bending due to its own weight, etc. This reduces the likelihood of problems caused by the curl cord's bending, such as interference with surrounding devices. Since the curl cord is less likely to interfere with surrounding devices, the expandable cable can be more easily routed in tight spaces. Furthermore, because the restricting member is expandable, the expansion and contraction of the curl cord is less likely to be hindered by the restricting member.

[0016] [2] In the above aspect [1], the restricting member may be configured as a core member inserted into the hollow portion of the curled portion. In this case, the restricting member is highly effective in suppressing bending of the curled cord. In addition, the space occupied by the entire elastic cable can be kept small, making it easier to route the elastic cable in limited spaces.

[0017] [3] In the aspect [2] above, the restricting member may be stretchable by having a structure in which multiple connecting pieces made of a material with higher rigidity than the cable are connected to each other so as to be movable in the axial direction. In this case, since the restricting member is made of a highly rigid material rather than an elastic body such as rubber, even if the restricting member is repeatedly stretched and contracted, the elasticity is less likely to decrease due to deterioration of the material over time. Therefore, in addition to the high durability of the curl cord, the expandable cable as a whole has high durability.

[0018] [4] In the above aspect [3], the plurality of connecting pieces may be configured as a plurality of tubular members having different diameters, and the tubular members having smaller diameters may be expanded or contracted by moving in and out of the hollow portions of the tubular members having larger diameters. In this case, a restricting member having a large amount of expansion and contraction can be formed with a simple structure while using a highly rigid material.

[0019] [5] Alternatively, in the above aspect [1], the restricting member may be configured as a sheath surrounding the outer periphery of the curled portion. In this case, even when the curled portion is thin and the hollow portion is narrow, the restricting member can be disposed along the axial direction of the curled portion, making it easier to provide the curl cord with a bending suppression function, regardless of the structure of the curled cord. Furthermore, the restricting member not only suppresses bending of the curled cord, but also serves a protective role.

[0020] [6] In the above aspect [5], the restricting member may be a hollow body having a bellows structure along the axial direction. In this case, the restricting member as a sheath has a simple structure and exhibits high bending suppression effect and stretchability. Furthermore, since stretchability can be ensured without using an elastic body, the decrease in stretchability of the restricting member due to deterioration over time of the material is suppressed, and combined with the high durability of the curl cord, the entire expandable cable can have high durability.

[0021] [7] In any one of the above aspects [1] to [6], the cable may include a plurality of electric wires and a covering material covering the outer periphery of the assembly of the plurality of electric wires. In this case, the covering material contributes to maintaining the flexibility of the curl cord even after repeated extension and contraction, and the durability of the curl cord can be effectively increased.

[0022] [Details of Embodiment of Present Disclosure] An expansion cable according to an embodiment of the present disclosure will be described in detail below with reference to the drawings.

[0023] <Stretchable Cable Configuration> First, the configuration of a stretchable cable according to one embodiment of the present disclosure will be described. Fig. 1 is a perspective view showing a stretchable cable 1 according to one embodiment of the present disclosure. The stretchable cable 1 includes a curl cord 2 and a restricting member 3. Fig. 1 shows the curl cord 2 and the restricting member 3 in their natural state, where no force is applied to them. In other words, the curl cord 2 is at its natural length.

[0024] The curl cord 2 has a curl portion 2a in which the cable 21 is wound in a spiral shape. The curl cord 2 is expandable and contractible in the curl portion 2a along the axial direction A, which corresponds to the direction of the central axis of the spiral shape. In the spiral shape, a gap S is provided between adjacent spiral turns along the axial direction A. As will be explained in detail later, the presence of this gap S allows the curl cord 2 to be displaced in both directions of expansion and contraction, contributing to improving the durability of the expandable cable 1 and reducing the load required for elongation. In the illustrated embodiment, portions where the cable 21 is maintained in a linearly stretched state are provided integrally at both ends of the curl portion 2a.

[0025] The configuration of the cable 21 used in the curl cord 2 is not particularly limited, and the cable 21 may be made of a single electric wire, such as an insulated electric wire with an insulating coating provided on the outer periphery of a conductor, or may include multiple electric wires. Furthermore, when multiple electric wires are included, the cable 21 may be made by assembling multiple electric wires by bundling, twisting, fusing, or the like, or the cable 21 may be configured by including a coating material that covers the outer periphery of the assembly in addition to the assembly of multiple electric wires.

[0026] The restricting member 3 is a member arranged along the axial direction A. The restricting member 3 is configured as a member that is less likely to bend than the curl cord 2 in a direction intersecting the axial direction A and is expandable and contractible along the axial direction A. The restricting member 3 serves to restrict the bending of the curl cord 2. While the detailed arrangement and structure of the restricting member 3 are not particularly limited, in the illustrated embodiment, the restricting member 3 is configured as a core inserted into the spiral-shaped hollow portion of the curl portion 2a. The inner circumferential surface of the curl portion 2a is not joined to the restricting member 3, allowing the curl cord 2 to expand and contract independently of the restricting member 3. Note that the restricting member 3 being less likely to bend than the curl cord 2 means that the amount of deformation of the restricting member 3 when a force is applied in a direction intersecting the axial direction A, particularly the amount of deformation due to its own weight when the axial direction A is horizontal, is smaller than that of the curl cord 2.

[0027] In the illustrated embodiment, the restricting member 3 has a structure in which multiple connecting pieces 31, made of a material with higher rigidity than the cable 21 constituting the curl cord 2, are connected to each other so as to be movable relative to one another along the axial direction A. The movement of the connecting pieces 31 relative to one another allows the restricting member 3 to expand and contract along the axial direction A. Specifically, the multiple connecting pieces 31 are configured as tubular members with different diameters, and the tubular members with smaller diameters move in and out of the hollow portions of the tubular members with larger diameters, allowing the restricting member 3 to expand and contract. Preferably, as shown in the figure, multiple tubular members are connected coaxially in the axial direction A in ascending order of diameter. A material with higher rigidity than the cable 21 refers to a material that is less likely to deform in each direction than the cable 21 when the same external force is applied. Specific examples of materials for the restricting member 3 include resin materials and metal materials. Resin materials exclude elastic bodies such as rubber, elastomers, and foamed resins.

[0028] <Expansion and contraction of the expandable cable> The expandable cable 1 is used by connecting one end and the other end of the curl cord 2 to two members (relatively movable members) that are movable relative to each other. For example, in an automobile, one end of the curl cord 2 is connected to a device fixed to the vehicle body, and the other end is connected to a device fixed to a movable seat. Both ends of the restricting member 3 in the axial direction A may or may not be connected to these relatively movable members.

[0029] When tension is applied to the curl cord 2 along the axial direction A due to movement of a relative moving member, such as movement of a sheet, the curl cord 2 is stretched as shown in Fig. 2. In other words, the gaps S between the turns widen, and the curl cord 2 is displaced in a direction extending its entire length along the axial direction A. The restricting member 3 receives tension from the relative moving member, or is pulled by the curl cord 2 that is displaced in the stretching direction, and stretches along the axial direction A to follow the curl cord 2.

[0030] On the other hand, when a compressive force is applied to the curl cord 2 along the axial direction A due to movement of the relative moving member, the curl cord 2 is compressed, as shown in Fig. 3. In other words, the gaps S between the turns narrow, and the curl cord 2 is displaced in a direction that shortens its overall length along the axial direction A. In the illustrated embodiment, the gaps S have disappeared. The restricting member 3 is compressed in the axial direction A to follow the curl cord 2 when it receives a compressive force from the relative moving member or is pulled by the curl cord 2 that is displaced in the compression direction.

[0031] As described above, in the expandable cable 1 according to this embodiment, the curl cord 2 has gaps S between the spiral turns, allowing it to displace in both the elongation and compression directions. Therefore, the amount of displacement required for the curl cord 2 to follow the movement of the relative moving member can be achieved by utilizing displacement in both the elongation and compression directions. If, as in conventional general curl cords, there are no gaps S between the spiral turns at their natural length and the cable is in (near) contact with adjacent turns, the curl cord 2 can only displace in the elongation direction. Therefore, the amount of displacement required for the curl cord 2 to follow the movement of the relative moving member must be achieved solely by displacement in the elongation direction.

[0032] 4A and 4B show the relationship between displacement and load in the curl cord 2 when there is and is not a gap S between the turns. In Fig. 4A, the horizontal axis shows displacement, and the vertical axis shows the load required to cause displacement, for the case when there is no gap S between the turns, and Fig. 4B, for the case when there is a gap S between the turns. The configuration of the cable 21 that makes up the curl cord 2 and the diameter of the spiral shape are the same in Fig. 4A and Fig. 4B.

[0033] When the gap S shown in FIG. 4A is not provided, the curl cord 2 cannot be compressed from its natural length, so the required displacement W must be achieved only in the extension direction. The load corresponding to this displacement is designated as L1. On the other hand, when the gap S shown in FIG. 4B is provided, the curl cord 2 can be displaced from its natural length in both the extension and compression directions, so the required displacement W can be achieved across both the extension and compression directions. Therefore, the maximum load required for expansion and contraction and the maximum load required for compression (both designated as L2 in the figure) can be reduced compared to when the same displacement W is achieved only by extension or compression from its natural length. In other words, the load required to achieve the same displacement W can be reduced (L2<L1) compared to when the curl cord 2 can be displaced only in the extension direction as shown in FIG. 4A.

[0034] As described above, in the expandable cable 1 according to this embodiment, by providing gaps S between the turns of the curl cord 2, the curl cord 2 can be displaced in both the extension and compression directions. By utilizing displacement in both directions to cover the required displacement width W, the load required for expansion and contraction can be reduced. This reduces the load applied to the cable 21 that constitutes the curl cord 2 as the curl cord 2 expands and contracts, thereby suppressing deterioration of the constituent materials of the cable 21 due to the applied load. As a result, the durability of the curl cord 2 is increased. In other words, the curl cord 2 maintains high elasticity even after repeated expansion and contraction. Furthermore, by reducing the load required for expansion and contraction of the curl cord 2, the force required for operating the relative moving member to which the curl cord 2 is connected can be reduced. In particular, by reducing the tension required for extension of the curl cord 2, the convenience of operating the relative moving member to which the curl cord 2 is connected, such as a car seat, is improved. In order to efficiently utilize the displacement of the curl cord 2 in both the extension direction and the compression direction, it is advisable to connect the curl cord 2 to a relative moving member, such as a car seat, so that the curl cord 2 takes on its natural length when the relative moving member is positioned in the middle of the required range of movement.

[0035] As described above, the expandable cable 1 according to this embodiment can utilize displacement in both directions of expansion and contraction, thereby achieving higher durability compared to a case in which only displacement in the extension direction is utilized, even if the constituent materials of the cable 21 are the same. Therefore, in order to improve durability, it is not necessary to use highly durable materials, such as materials with extremely high elastic moduli, as constituent materials of the cable 21, including the covering material. However, if the cable 21 itself has high durability, the durability of the curl cord 2 can be further effectively improved. For example, when the cable 21 is configured to include multiple electric wires, providing a covering material around the outer periphery of the assembly of these multiple electric wires increases the springiness of the curl cord 2, making it easier to ensure high elasticity even when the cable 21 is repeatedly expanded and contracted.

[0036] There are no particular limitations on the size of the gaps S in the curl cord 2. However, for example, if the ratio of the width of the region occupied by the gaps S along the axial direction A to the width of the region occupied by the cable 21 in the curled portion 2a (width of gap S / width of cable 21 × 100%) is set to 50% or more, the effects of improving durability and reducing the required load due to the gaps S in the curl cord 2 can be sufficiently enhanced. On the other hand, if the ratio is kept within an excessively large range, such as 500% or less, sufficient springiness in the curl cord 2 can be easily ensured.

[0037] Thus, by providing gaps S between the spiral turns of the curl cord 2, the durability of the curl cord 2 can be improved and the required load can be reduced. However, providing gaps S between the turns makes the curl cord 2 more likely to bend under its own weight or external force than when no gaps S are provided. Bending of the curl cord 2 can lead to interference with surrounding components. However, in the expandable cable 1 according to this embodiment, the curl cord 2 is not used alone, but a restricting member 3, which is less likely to bend than the curl cord 2, is arranged along the axis of the curl cord 2. Therefore, the restricting member 3 restricts bending of the curl cord 2, making it less likely to interfere with surrounding components due to bending. Avoiding interference with surrounding components makes it easier to route the curl cord 2 in narrow spaces, making the expandable electric cord 1 suitable for applications requiring high-density routing of the curl cord 2 in narrow spaces, such as inside and around automobile seats. While the restricting member 3 is less likely to bend, its ability to stretch along the axial direction A makes it less likely for the restricting member 3 to interfere with the stretching of the curl cord 2. In other words, the presence of the restricting member 3 makes it less likely that the curl cord 2 will not be able to fully extend, or that excess length will be generated in the restricting member 3 when the curl cord 2 is compressed, causing interference with relative moving members or surrounding members.

[0038] <Configuration of Restraining Member> Here, possible configurations of the restraining member 3 will be described. The restraining member 3 is not limited to the configuration described above, and can be applied to any configuration as long as it is less likely to bend in a direction intersecting the axial direction A than the curl cord 2 and is expandable along the axial direction A. Examples of types of restraining member 3 include a core material inserted into the hollow portion of the curled portion 2a of the curl cord 2, and a sheath material surrounding the outer periphery of the curled portion 2a of the curl cord 2. The core material configuration is particularly effective in suppressing the bending of the curl cord 2 and following the expansion and contraction of the curl cord 2, and is excellent in terms of space-saving for the entire expandable cable 1. On the other hand, the sheath material configuration is excellent in that it is easy to attach the restraining member 3 to various configurations of curl cords 2, such as when the hollow portion of the curl cord 2 is narrow, and that it can play a role in not only restricting bending but also providing physical protection for the curl cord 2. The restraining member 3 may be either a core material or a sheath material, or both.

[0039] A specific example of a core-shaped regulating member 3 is one in which the regulating member 3 is made of an elastic material such as rubber, elastomer, or foamed resin, and is stretchable along the axial direction A due to the elastic deformation of the material itself. The regulating member 3 may be configured as a continuous body, such as a rod. However, in this case, the material constituting the regulating member 3 itself expands and contracts as the curl cord 2 expands and contracts, making the material constituting the regulating member 3 prone to deterioration and breakage, such as rupture, as the regulating member 3 expands and contracts repeatedly. This reduces the durability of the regulating member 3. Furthermore, it is difficult to ensure a high expansion / contraction ratio for the regulating member 3. Typically, the expansion / contraction ratio remains at or below 2x.

[0040] In contrast, when a restricting member 3 is used in which multiple connecting pieces 31 made of a highly rigid material are connected to each other so as to be movable in the axial direction A, as in the embodiment described above in which the tubular connecting pieces 31 are connected, the restricting member 3 expands and contracts in the axial direction A due to the physical structure of the multiple connecting pieces 31, rather than the elasticity of the material that constitutes the restricting member 3. Therefore, even if the restricting member 3 is repeatedly expanded and contracted in response to the expansion and contraction of the curl cord 2, deterioration over time and accumulation of load in the restricting member 3 are unlikely to occur. Therefore, the restricting member 3 can maintain its effect of suppressing flexure of the curl cord 2 and its ability to follow the expansion and contraction of the curl cord 2 for a long period of time. This, combined with the high durability of the curl cord 2, results in high overall durability of the expandable cable 1. By utilizing the relative movement of the connecting pieces 31 rather than the expansion and contraction of the material to achieve expansion and contraction, a large expansion ratio of the restricting member 3 can be easily ensured. In particular, by configuring the connecting pieces 31 as tubular members, a large expansion ratio can be achieved with a simple structure. For example, an expansion ratio of approximately 3 to 5 times can be ensured. The highly rigid material that constitutes the connecting piece 31 is not particularly limited as long as it is a material that is more rigid than the cable 21, but generally, it is sufficient to use a material that has a strength that is such that irreversible deformation of the material does not occur when manually operated.

[0041] An example of a case in which the restricting member 3 takes the form of a sheath material is a case in which the restricting member 3 is configured as a hollow member that is expandable in the axial direction A, and the curled portion 2a of the curl cord 2 is housed within the hollow portion. Specifically, the restricting member 3 may be configured as a hollow cylindrical body made of an elastic material such as rubber, elastomer, or foamed resin, and the cylindrical body may expand and contract along the axial direction A due to the elastic deformation of the elastic material itself. However, in this case, as explained above in connection with the case in which the restricting member 3 is configured as a core material rather than an elastic material, the durability of the restricting member 3 is likely to be low. Furthermore, it is difficult to ensure a large expansion / contraction ratio.

[0042] As with the core-shaped regulating member 3, the sheath-shaped regulating member 3 can be expanded and contracted in the axial direction A not only by elastic deformation due to the physical properties of the material itself, but also by a physical structure, thereby improving durability and expansion / contraction ratio. An example of a physical structure that allows the sheath-shaped regulating member 3 to expand and contract is a regulating member 3 constructed as a hollow body having a bellows structure along the axial direction A. Examples of hollow bodies having a bellows structure include those known as bellows or flexible tubes. The use of a bellows structure allows for a regulating member 3 to be obtained with a simple structure that has a high bending suppression effect and expandability. In this case, too, it is preferable to use, as the constituent material of the regulating member 3, a material with a strength sufficient to prevent irreversible deformation of the material through manual operation, such as a hard resin material.

[0043] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention.

[0044] REFERENCE SIGNS LIST 1 Extendable cable 2 Curl cord 21 Cable 2a Curl portion 3 Regulating member 31 Connecting piece A Axial direction L1, L2 Load W Displacement width

Claims

1. An expandable cable comprising: a curl cord having a curled portion wound in a spiral shape, with gaps between adjacent turns of the spiral at its natural length; and a restricting member disposed along the axial direction of the curled portion, wherein the restricting member is less likely to bend than the curl cord in a direction intersecting the axial direction, and is expandable along the axial direction.

2. The elastic cable according to claim 1, wherein the restricting member is configured as a core material inserted into the hollow portion of the curled portion.

3. The retractable cable described in claim 2, wherein the restricting member is made stretchable by having a structure in which multiple connecting pieces made of a material with higher rigidity than the cable are connected to each other so that they can move in the axial direction.

4. An expandable cable as described in claim 3, wherein the multiple connecting pieces are configured as multiple tubular members of different diameters, and the smaller diameter tubular members are capable of expanding and contracting by moving in and out of the hollow portions of the larger diameter tubular members.

5. The elastic cable according to claim 1, wherein the restricting member is configured as a sheath material surrounding the outer periphery of the curled portion.

6. The elastic cable according to claim 5, wherein the restricting member is composed of a hollow body having a bellows structure along the axial direction.

7. An expandable cable according to any one of claims 1 to 6, wherein the cable comprises a plurality of electric wires and a covering material that covers the outer periphery of the assembly of the plurality of electric wires.

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