Power generation method for tire, power generation device for tire, and road surface state determination system

Abstract

In this power generation method for a tire, power is generated by rotating the tire. This power generation method includes: a step for rotating a tire in which a power generation device for the tire is disposed in an inner cavity; and a step for vibrating a piezoelectric film provided in the power generation device for the tire by means of air vibration in the inner cavity of the tire and generating power by the piezoelectric film.

Description

Tire power generation method, tire power generation device, and road surface condition determination system

[0001] The present disclosure relates to a tire power generation method, a tire power generation device, and a road surface condition determination system.

[0002] Conventionally, a sensor module has been installed inside the tire cavity of a vehicle. To operate this sensor module, various types of power generation devices have been installed inside the tire cavity. As an example of a power generation device, Japanese Patent Application Laid-Open No. 2006-54956 describes a device in which a weight is installed inside the tire cavity and vibrates as the vehicle travels, generating power using the principle of electromagnetic induction.

[0003] As mentioned above, there is a method of generating electricity by using a power generator installed inside the tire as the tire rotates. However, in the method using the weight, if the weight cannot vibrate appropriately, the power generation efficiency is low.

[0004] Therefore, the present disclosure describes a tire power generation method, a tire power generation device, and a road surface condition determination system that can generate electricity more efficiently as the tire rotates.

[0005] The tire power generation method according to the present disclosure is a method of generating electricity by rotating a tire, and includes the steps of rotating a tire having a tire power generation device disposed within the tire cavity, and introducing air vibrations within the tire cavity into a resonance box of the tire power generation device, causing a piezoelectric film provided on the tire power generation device to vibrate due to the air vibrations generated by resonance in the resonance box, and generating electricity using the piezoelectric film.

[0006] In this tire power generation method, air vibrations within the tire cavity caused by the rotation of the tire are introduced into a resonance box, and the air vibrations generated by the resonance of the resonance box can vibrate the piezoelectric film. Here, sound pressure is high within the tire cavity. Furthermore, because the tire cavity is sealed, acoustic energy is not diffracted or diffused. Therefore, in this tire power generation method, the air vibrations within the tire cavity can efficiently vibrate the piezoelectric film. In this way, this tire power generation method can generate electricity more efficiently as the tire rotates.

[0007] The tire power generating device according to the present disclosure is a tire power generating device that is placed within the inner cavity of a tire and is used in the tire power generating method described above. The tire power generating device comprises: an outer wall; a hollow portion formed within the outer wall; a resonance box having a first opening that opens the hollow portion to the outside of the outer wall and introduces air vibrations into the hollow portion; and a second opening that opens the hollow portion to the outside of the outer wall; and a piezoelectric film attached to the resonance box so as to cover the second opening.

[0008] As described above, the sound pressure inside the tire cavity is high and the tire cavity is sealed. Therefore, the tire generator can efficiently vibrate the piezoelectric film. The tire generator also includes a resonance box having an outer wall, a hollow portion formed in the outer wall, and a first opening and a second opening for introducing air vibrations into the hollow portion. The second opening is covered with a piezoelectric film. Therefore, the tire generator can introduce air vibrations into the hollow portion from the first opening, allowing the resonance box to function as a Helmholtz resonance sound absorber. The tire generator can then vibrate the piezoelectric film provided at the second opening of the resonance box using the air vibrations generated by resonance in the resonance box. In this way, the tire generator can generate electricity more efficiently as the tire rotates and reduce resonance noise inside the tire cavity.

[0009] In the tire generator described above, the resonance box may include a hollow neck portion that communicates between the first opening and the hollow portion. In this tire generator, the resonance box includes a hollow neck portion that communicates between the first opening and the hollow portion, and therefore the resonant frequency of Helmholtz resonance can be adjusted by adjusting the length of the neck portion. Furthermore, by lengthening the neck portion, Helmholtz resonance with a resonant frequency in the low-frequency range can be generated, thereby reducing low-frequency resonance sounds such as tire cavity resonance sounds.

[0010] In the tire generator described above, at least a portion of the neck may be disposed within the outer wall. In this tire generator, since at least a portion of the neck is disposed within the outer wall, it is possible to lengthen the neck and generate Helmholtz resonance with a resonant frequency in the low frequency range, while also achieving a reduction in the size of the tire generator.

[0011] In the above-described generator for a tire, the end of the neck portion on the hollow portion side may be open toward the piezoelectric film, thereby allowing the resonant vibration of the air generated in the neck portion to be efficiently applied to the piezoelectric film via the air in the hollow portion.

[0012] In the tire generator described above, the outer wall may include a bottom wall portion attached to the inner cavity surface of the tire and a top wall portion forming a hollow portion between the bottom wall portion and the outer wall, and the neck portion may be disposed on the bottom wall portion so as to extend along the bottom wall portion. In this tire generator, since the neck portion is disposed on the bottom wall portion so as to extend along the bottom wall portion, movement of the neck portion due to centrifugal force can be suppressed.

[0013] In the above-described tire generator, the resonance box may be configured to be long in a first direction, and the first opening may be formed at an end of the outer wall in the first direction. In this tire generator, the resonance box is configured to be long in the first direction, and the first opening is formed at an end of the outer wall in the first direction, so that the resonance box can be made compact while the neck portion can be made long.

[0014] In the tire generator described above, the second opening may be formed at an end of the outer wall opposite the first opening in the first direction. In this tire generator, the first opening and the second opening are provided at both longitudinal ends of the resonance box. Therefore, in this tire generator, the resonance box can be made smaller, and the neck portion disposed between the first opening and the second opening can be made longer.

[0015] In the tire generator described above, the top wall portion may be convexly curved. In this tire generator, the top wall portion of the outer wall is convexly curved, which makes it easier to absorb forces directed toward the bottom wall portion. This makes it possible to prevent deformation of the resonance box of the tire generator due to centrifugal force generated when a vehicle equipped with the tire generator mounted on the tire cavity surface is driven at high speed. Furthermore, in this tire generator, deformation of the resonance box is prevented, which also prevents deformation of the piezoelectric film attached to the resonance box. As a result, in this tire generator, deformation of the resonance box is prevented, which allows the piezoelectric film to vibrate more appropriately and prevents a decrease in power generation efficiency due to the piezoelectric film.

[0016] In the tire generator described above, the top wall portion may be formed in an arc shape in a cross section perpendicular to the first direction. In this tire generator, since the top wall portion is formed in an arc shape in a cross section perpendicular to the first direction, deformation of the top wall portion due to centrifugal force can be effectively suppressed.

[0017] In the tire generator described above, the resonance box may include a support portion that supports the top wall portion relative to the bottom wall portion. In this tire generator, the resonance box includes a support portion that supports the top wall portion relative to the bottom wall portion, which further reduces deformation of the top wall portion due to centrifugal force.

[0018] In the above-described tire generator, the support portion may extend from the bottom wall portion side to the top wall portion side in the hollow portion. In this tire generator, since the support portion extends from the bottom wall portion side to the top wall portion side in the hollow portion, it is possible to reduce the size of the tire generator and suppress deformation of the top wall portion due to centrifugal force.

[0019] The tire generator may further include a flange extending from the bottom wall toward the outside of the resonance box. Because this tire generator includes the flange extending from the bottom wall toward the outside of the resonance box, the flange can be pressed against the tire cavity surface. This makes it possible to easily attach the tire generator to the tire cavity surface.

[0020] In the above-described tire generator, the outer wall may have at least one of a Shore A hardness of 40 to 100 and a Shore D hardness of 10 to 70. In this tire generator, the outer wall has at least one of a Shore A hardness of 40 to 100 and a Shore D hardness of 10 to 70, so that deformation of the resonance box due to centrifugal force can be suppressed while the conformability to the tire cavity surface can be improved.

[0021] In the tire generator described above, the outer wall may include an elastomer. In this tire generator, since the outer wall includes an elastomer, deformation of the resonance box due to centrifugal force can be suppressed and conformability to the tire cavity surface can be improved.

[0022] The road surface condition determination system according to the present disclosure is a road surface condition determination system capable of determining the unevenness of the road surface on which a tire rolls, and includes the tire power generating device described above, a determination device that determines the unevenness of the road surface, and a transmission device that transmits electromotive force information including the magnitude of the electromotive force generated in the piezoelectric film to the determination device, wherein the transmission device transmits the electromotive force information using the power generated by the piezoelectric film, and the determination device determines the magnitude of the unevenness of the road surface based on the magnitude of the electromotive force included in the electromotive force information obtained from the transmission device, or determines the spacing between the unevenness of the road surface based on the period of change in the electromotive force.

[0023] When a tire rolls over an uneven road surface, the road surface unevenness causes air vibrations within the tire cavity. In other words, there is a correlation between the air vibrations generated within the tire cavity and the road surface unevenness. Therefore, the determination device of the road surface condition determination system can determine the road surface unevenness by using electromotive force information from the piezoelectric film of the tire generator as information about the air vibrations within the tire cavity. The determination device determines the magnitude of road surface unevenness based on the magnitude of the electromotive force contained in the electromotive force information, or determines the distance between road surface unevenness based on the period of change in electromotive force. This allows the determination device to more appropriately determine the road surface unevenness. Furthermore, in the road surface condition determination system, the tire generator can generate electricity more efficiently as the tire rotates, as described above. This allows the road surface condition determination system to operate the transmitter using the generated power of the tire generator and stably transmit electromotive force information to the determination device. In this way, the road surface condition determination system can determine the road surface unevenness while generating electricity more efficiently as the tire rotates.

[0024] According to various aspects of the present disclosure, power can be generated more efficiently as the tire rotates.

[0025] FIG. 1 is a block diagram showing the overall configuration of a road surface condition determination system including a power generation device according to an embodiment. FIG. 2 is a schematic cross-sectional view of a tire equipped with a power generation device. FIG. 3 is a schematic perspective view of the power generation device according to an embodiment, viewed from the first opening side. FIG. 4 is a schematic perspective view of the power generation device according to an embodiment, viewed from the piezoelectric film side. FIG. 5 is a schematic cross-sectional view taken along line V-V in FIG. 3. FIG. 6 is a schematic cross-sectional view taken along line VI-VI in FIG. 3. FIG. 7 is a diagram illustrating a method for calculating the resonant frequency of a Helmholtz resonance structure. FIG. 8 is a schematic diagram showing the distribution of sound pressure within the tire cavity. FIGS. 9(a) to 9(c) are schematic diagrams showing the relative positions of two power generation devices with respect to the excitation position of the tire. FIG. 10(a) is a graph showing the electromotive force waveforms of the first power generation device at various tire rotational states. FIG. 10(b) is a graph showing the electromotive force waveforms of the second power generation device at various tire rotational states. FIG. 11 is a graph showing changes in average sound pressure obtained by averaging the sound pressure at the position of the first power generator and the sound pressure at the position of the second power generator. FIG. 12 is a diagram showing changes in average sound pressure when a tire goes over protrusions of different sizes. FIG. 13 is a diagram showing changes in the waveform of the average sound pressure calculated by the determination device. FIG. 14 is a flowchart showing the flow of a process for determining the unevenness of a road surface performed in a road surface condition determination system. FIG. 15 is a flowchart showing the flow of a tire power generation method. FIG. 16 is a schematic cross-sectional view of a power generator according to a first modified example. FIG. 17 is a schematic cross-sectional view of a power generator according to a second modified example. FIG. 18 is a schematic cross-sectional view taken along line XVIII-XVIII in FIG. 17. FIG. 19 is a schematic cross-sectional view taken along line XIX-XIX in FIG. 17. FIG. 20 is a schematic perspective view of a power generator according to a third modified example. FIG. 21 is a schematic cross-sectional view taken along line XXI-XXI in FIG. 20. FIG. 22 is a schematic cross-sectional view of a tire to which a power generation device of a road surface condition determination system according to a modified example is attached.

[0026] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0027] Fig. 1 is a block diagram showing the overall configuration of a road surface condition determination system including a power generation device according to an embodiment. Fig. 2 is a schematic cross-sectional view of a tire to which the power generation device is attached. The road surface condition determination system 100 generates electricity as the tire T rotates, and determines the unevenness of the road surface on which the tire T rolls. The power generation device 1 (tire power generation device) and the transmitter 2 are provided inside the cavity S of the tire T. The determination device 3 is provided outside the cavity S of the tire T. The cavity S of the tire T is an annular space defined by the outer peripheral surface of the wheel H on which the tire T is mounted and the inner surface of the tire T.

[0028] The power generation device 1 is a tire power generation device used in a tire power generation method. In this embodiment, two power generation devices 1 are provided in the inner cavity S of the tire T. The transmitter 2 transmits electromotive force information, including the magnitude of the electromotive force generated by the power generation device 1, to the determination device 3. The transmitter 2 can communicate with the determination device 3 using wireless communication. In this embodiment, a transmitter 2 is provided for each of the multiple power generation devices 1. That is, in this embodiment, two transmitters 2 are provided. However, a configuration in which one transmitter 2 is provided for each of the multiple power generation devices 1 may also be used. When one transmitter 2 is provided for each power generation device 1, the transmitter 2 transmits electromotive force information of the corresponding power generation device 1 to the determination device 3. When one transmitter 2 is provided for each of the multiple power generation devices 1, the transmitter 2 transmits electromotive force information of the corresponding power generation device 1 to the determination device 3.

[0029] Here, in the tire T, cavity resonance may occur, in which the air in the lumen S resonates due to vibrations caused by passing over uneven road surfaces while the vehicle is traveling. The frequency of cavity resonance is approximately 200 Hz to 300 Hz, typically approximately 250 Hz. The power generating device 1 according to this embodiment is attached to the lumen surface Ta of the tire T in order to efficiently absorb cavity resonance in the low frequency band. The lumen surface Ta is the inner circumferential surface of the tread Tb. The power generating device 1 is attached to the lumen surface Ta of the tire T, for example, by double-sided adhesive tape TP attached to the attachment surface 10a of the power generating device 1. The attachment surface 10a is the surface (back surface) of the power generating device 1 that is attached to the lumen surface Ta of the tire T. In this embodiment, the two power generating devices 1 are attached to the lumen surface Ta at positions offset by 90° in the rotational direction of the tire T. However, the power generating device 1 is not limited to being attached to the lumen surface Ta, which is the inner circumferential surface of the tread Tb. For example, the power generating device 1 may be attached to the outer circumferential surface of the wheel H within the bore S.

[0030] The transmitter 2, like the power generation device 1, is attached to the lumen surface Ta of the tire T by, for example, double-sided adhesive tape. The transmitter 2 may be disposed adjacent to the power generation device 1, or may be disposed apart from the power generation device 1. Note that the power generation device 1 and the transmitter 2 are not limited to being attached by using double-sided adhesive tape TP, and may be attached by any appropriate method, such as by using an adhesive.

[0031] The power generating device 1 according to the embodiment will be described with reference to Figs. 3 to 6. Fig. 3 is a schematic perspective view of the power generating device according to the embodiment, viewed from the first opening side. Fig. 4 is a schematic perspective view of the power generating device according to the embodiment, viewed from the piezoelectric film side. Fig. 5 is a schematic cross-sectional view taken along line V-V in Fig. 3. Fig. 6 is a schematic cross-sectional view taken along line VI-VI in Fig. 3. Note that Fig. 5 is also a schematic cross-sectional view taken along line V-V in Fig. 6. Fig. 6 is also a schematic cross-sectional view taken along line VI-VI in Fig. 5.

[0032] As shown in Figures 3 to 6, the power generation device 1 according to this embodiment includes a resonance box 10 and a piezoelectric film 20. The resonance box 10 has a Helmholtz resonance structure. The resonance box 10 includes an outer wall 11, a hollow portion 12 formed within the outer wall 11, a first opening 13 that opens the hollow portion 12 to the outside of the outer wall 11 (outside the resonance box 10), a second opening 14 that opens the hollow portion 12 to the outside of the outer wall 11, and a hollow neck portion 15 that connects the first opening 13 to the hollow portion 12. The first opening 13 introduces air vibrations from the outside of the outer wall 11 (outside the resonance box 10) into the hollow portion 12.

[0033] The outer wall 11 has self-supporting properties to the extent that it can maintain its shape in a stationary state. The outer wall 11 is non-breathable. The outer wall 11 has at least one of a Shore A hardness of 40 to 100 and a Shore D hardness of 10 to 70. In this case, the Shore A hardness of the outer wall 11 may be 50 to 80 or 60 to 70. The Shore D hardness of the outer wall 11 may be 10 to 50 or 10 to 40.

[0034] The Shore A hardness of the outer wall 11 can be measured using a durometer in accordance with JIS K6253-3:2012, and for example, a GS-709N TYPE A manufactured by Teclock Corporation can be used. The Shore D hardness of the outer wall 11 can be measured using a durometer in accordance with JIS K6253-3:2012, and for example, a GS-720N TYPE D manufactured by Teclock Corporation can be used. If the allowable number of stacked test pieces (3 or less) specified in JIS K6253-3:2012 does not satisfy the specified measurement thickness (6 mm or more), more than 3 pieces can be stacked and measured at the specified thickness.

[0035] The material of the outer wall 11 includes, for example, an elastomer such as a thermoplastic elastomer, a plastic, a rubber, a rubber-like material, or other resin.

[0036] Examples of elastomer materials include thermoplastic elastomers such as styrene block copolymer (SBC), polyolefin (TPO), polyurethane (TPU), polyester (TPC), polyamide (TPA), dynamically crosslinked (TPV), soft polyvinyl chloride (PVC), and acrylic.

[0037] Examples of plastic materials include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyphenylene sulfide (PPS), polyurethane (PU), epoxy resin, phenolic resin, and melamine resin.

[0038] Examples of rubber materials include natural rubber (NR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), silicone rubber, and urethane rubber.

[0039] Examples of rubber-like materials include UV-curable acrylic rubber-like materials.

[0040] The first opening 13 is formed in the outer wall 11 and penetrates the outer wall 11. The first opening 13 serves as an entrance for tire cavity resonance sound in the resonance box 10. The shape (cross-sectional shape) of the first opening 13 is not particularly limited, and may be various shapes such as a circle, a triangle, a rectangle, a polygon, or an ellipse. In this embodiment, the first opening 13 is a circular hole. That is, the cross-sectional shape of the first opening 13 is circular. The inner diameter of the first opening 13 is, for example, approximately 1 mm to 5 mm.

[0041] The second opening 14 is formed in the outer wall 11 and penetrates the outer wall 11. The second opening 14 is formed at an end of the outer wall 11 opposite the first opening 13 in the first direction D1. That is, the first opening 13 and the second opening 14 are provided at both end portions of the outer wall 11 in the first direction D1. The shape (cross-sectional shape) of the second opening 14 is not particularly limited and may be various shapes such as a circle, a triangle, a rectangle, a polygon, or an ellipse. In this embodiment, the size of the second opening 14 is larger than that of the first opening 13.

[0042] The outer wall 11 includes a bottom wall portion 11a, a top wall portion 11b, and a side wall portion 11c. The thickness of the outer wall 11 is, for example, about 0.1 mm to 2 mm. That is, the thickness of each of the bottom wall portion 11a, the top wall portion 11b, and the side wall portion 11c is, for example, about 0.1 mm to 2 mm.

[0043] The bottom wall portion 11a is a portion that forms the mounting surface 10a. The bottom wall portion 11a is located on the mounting surface 10a side of the hollow portion 12 and covers the hollow portion 12 from the mounting surface 10a side. The bottom wall portion 11a is formed in the shape of a rectangular plate that is long in the first direction D1 and short in the second direction D2 perpendicular to the first direction D1. The direction perpendicular to the first direction D1 and the second direction D2 is called the third direction D3. The third direction D3 is also the thickness direction or height direction of the resonance box 10.

[0044] The top wall portion 11b is a portion that forms the hollow portion 12 between itself and the bottom wall portion 11a. The top wall portion 11b is located on the opposite side of the hollow portion 12 from the mounting surface 10a and covers the hollow portion 12 from the opposite side of the mounting surface 10a. The top wall portion 11b is convexly curved. The top wall portion 11b being convexly curved means that the top wall portion 11b is curved so as to be convex on the side opposite the bottom wall portion 11a in the third direction D3, so as to be convex in the direction away from the bottom wall portion 11a, or so as to be convex on the side opposite the hollow portion 12. Specifically, the top wall portion 11b is formed in an arc shape (arch-like) in a cross section perpendicular to the first direction D1 (a cross section along the second direction D2 and the third direction D3). Both ends of the top wall portion 11b in the second direction D2 are connected to both ends of the bottom wall portion 11a in the second direction D2. In other words, the top wall portion 11b is formed in the shape of an arc-shaped curved plate so that it is convex on the opposite side to the bottom wall portion 11a in the third direction D3, and is connected to one end of the bottom wall portion 11a in the second direction D2 and the other end of the bottom wall portion 11a that is opposite to the one side in the second direction D2.

[0045] The side wall portion 11c is a portion located at one end of the outer wall 11 in the first direction D1. The side wall portion 11c is located on one side of the hollow portion 12 in the first direction D1 and covers the hollow portion 12 from one side in the first direction D1. A first opening 13 is formed in the side wall portion 11c. That is, the first opening 13 penetrates the side wall portion 11c and communicates with the hollow portion 12. The side wall portion 11c is formed in a flat plate shape extending in a direction intersecting the first direction D1 and is connected to one end of the bottom wall portion 11a and the top wall portion 11b in the first direction D1. In this embodiment, the side wall portion 11c is formed in a flat plate shape extending in a direction perpendicular to the first direction D1 (a direction along the second direction D2 and the third direction D3).

[0046] The outer wall 11 does not have a wall portion at the end opposite to the side where the side wall portion 11c is provided in the first direction D1. The outer wall 11 is open at the end opposite to the side where the side wall portion 11c is provided in the first direction D1. This open portion of the outer wall 11 becomes the second opening 14. The second opening 14 is provided at the other end opposite to the one side of the outer wall 11 in the first direction D1.

[0047] The length of the resonance box 10 (external wall 11), which includes the bottom wall 11a, the top wall 11b, and the side wall 11c, in the first direction D1 is, for example, about 30 mm to 80 mm. The length of the resonance box 10 in the second direction D2 is, for example, about 20 mm to 50 mm. The length of the resonance box 10 in the third direction D3 (i.e., the height of the resonance box 10) is, for example, about 20 mm to 50 mm.

[0048] At least a portion of the neck portion 15 is disposed within the outer wall 11. In this embodiment, the entire neck portion 15 is disposed within the outer wall 11. The base end and tip end of the neck portion 15 are open ends at which a hollow portion 15a of the neck portion 15 is exposed. The base end of the neck portion 15 is connected to the first opening 13. The hollow portion 15a of the neck portion 15 opens from the first opening 13 to the outside of the outer wall 11 (outside the resonance box 10) at the base end of the neck portion 15. The tip end of the neck portion 15 is located within the hollow portion 12. The hollow portion 15a of the neck portion 15 opens to the hollow portion 12 at the tip end of the neck portion 15. The end of the neck portion 15 on the hollow portion 12 side opens toward the piezoelectric film 20.

[0049] The neck portion 15 is non-air permeable, similar to the resonance box 10. The neck portion 15 has at least one of the Shore A hardness and the Shore D hardness similar to the resonance box 10. The material of the neck portion 15 can be the same as the material of the resonance box 10.

[0050] The hollow portion 15a of the neck portion 15 has, for example, a cross section that is equal to or larger than the cross section of the first opening 13. By increasing the extension length of the neck portion 15, the resonance frequency of the resonance box 10 can be lowered. In other words, by increasing the extension length of the neck portion 15, resonance sounds in the low frequency range can be reduced. The extension length of the neck portion 15 is the length of the extension axis of the neck portion 15 from the base end of the neck portion 15 to the tip end of the neck portion 15.

[0051] The neck portion 15 is disposed on the bottom wall portion 11a so as to extend along the bottom wall portion 11a. For example, the neck portion 15 is integrally formed (integrally molded) with the bottom wall portion 11a and connected to the bottom wall portion 11a. The neck portion 15 extends in the first direction D1, but the extending direction, extending shape, etc. of the neck portion 15 are not particularly limited. Furthermore, the neck portion 15 may be provided as a separate body (separate part) from the bottom wall portion 11a. The neck portion 15 may be detachable from the outer wall 11.

[0052] The resonance box 10 configured in this manner can be manufactured by, for example, injection molding, extrusion molding, modeling using a 3D printer, salt coagulation method, or the like.

[0053] The piezoelectric film 20 is attached to the outer wall 11 so as to cover the second opening 14. Like the resonance box 10, the piezoelectric film 20 is non-breathable. The piezoelectric film 20 is attached to the outer wall 11 so as to tightly cover the second opening 14. The piezoelectric film 20 is located on the other side of the hollow portion 12, opposite one side (the side wall portion 11c side) in the first direction D1, and covers the hollow portion 12 from the other side in the first direction D1. The piezoelectric film 20 generates an electromotive force when stress is applied. The piezoelectric film 20 has a conductive layer such as copper foil and can output power to the outside. The piezoelectric film 20 generates power when vibrated by the vibration of air in the cavity S.

[0054] The piezoelectric film 20 contains a piezoelectric material. The piezoelectric material may be, for example, in the form of particles. Examples of the piezoelectric material include ceramic-based piezoelectric materials and polymer-based piezoelectric materials. From the viewpoint of obtaining good piezoelectric performance, the piezoelectric material is preferably a ceramic-based piezoelectric material.

[0055] Examples of ceramic piezoelectric materials include barium titanate (BT) piezoelectric materials, lead zirconate titanate (PZT) piezoelectric materials, lead lanthanum zirconate titanate (PLZT) piezoelectric materials, and lead titanate (PT)-lead zirconate (PZ) piezoelectric materials. Specific examples of ceramic piezoelectric materials include barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ ), lithium niobate (Li ２ NbO ３ ), lithium titanate (LiTiO ３ ), lead titanate (PbTiO ３ ), barium lead titanate ((Ba,Pb)TiO ３ ), barium calcium titanate ((Ba,Ca)TiO ３ ), potassium sodium niobate ((K,Na)NbO ３ ), potassium lithium niobate ((K,Li)NbO ３ ), and lead zirconate titanate (Pb(Zr,Ti)O ３ ) are listed.

[0056] Examples of polymer-based piezoelectric materials include polyvinylidene fluoride, polytetrafluoroethylene, iodinated polyvinyl acetate, polyurea, and polylactic acid.

[0057] The piezoelectric film 20 may further contain a matrix in addition to the piezoelectric material. In this case, the piezoelectric material, for example, particulate piezoelectric material, may be dispersed in the matrix.

[0058] The matrix may be, for example, a resin such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene (PTFE), ABS resin (acrylonitrile butadiene styrene resin), acrylic resin, polyamide, polycarbonate, polyethylene terephthalate (PET), thermoplastic polyimide, phenolic resin, epoxy resin, melamine resin, or polyimide (excluding the above-mentioned polymeric piezoelectric materials).

[0059] From the viewpoint of providing the piezoelectric film 20 with excellent flexibility, heat resistance, elongation, etc., the matrix may preferably be an acrylic resin containing, as monomer units, a compound represented by the following formula (1), a compound represented by the following formula (2), a compound represented by the following formula (3), and other polymerizable compounds. In formula (1), R １１ and R １２ each independently represents a hydrogen atom or a methyl group, R １３ represents a divalent group having a polyoxyalkylene chain. In formula (2), R ２１ and R ２２ each independently represents a hydrogen atom or a methyl group, R ２３ represents a divalent group having a poly(meth)acrylate chain. In formula (3), R ３１ and R ３２ R each independently represents a hydrogen atom or a monovalent organic group, and may be bonded to each other to form a ring. ３３ represents a hydrogen atom or a methyl group.

[0060] R １３ The polyoxyalkylene chain in may be a divalent group having a polyoxyethylene chain, a divalent group having a polyoxypropylene chain, or a divalent group having a copolymer chain of a polyoxyethylene chain and a polyoxypropylene chain. The copolymer chain may be any of an alternating copolymer chain, a block copolymer chain, and a random copolymer chain.

[0061] R ２３ The poly(meth)acrylate chain in may contain a structural unit represented by the following formula (2a): In formula (2a), R ２４ represents a hydrogen atom or a monovalent organic group, R ２５ represents a hydrogen atom or a methyl group.

[0062] R ２４ The monovalent organic group represented by the formula (I) may be, for example, a hydrocarbon group, an alkyl group, or an organic group having an oxygen atom, a nitrogen atom, or the like.

[0063] R ３１ and R ３２ When R are not bonded to each other to form a ring, the monovalent organic group may be, for example, a monovalent hydrocarbon group or an alkyl group. ３１ and R ３２ are preferably bonded to each other to form a ring. In this case, the ring may be, for example, a six-membered ring. The ring is formed by bonding a nitrogen atom and R ３１ and R ３２ and a group represented by the following formula (1): and may contain, in addition to the nitrogen atom, a carbon atom, a hydrogen atom, an oxygen atom, a sulfur atom, etc.

[0064] The other polymerizable compound may be, for example, an alkyl(meth)acrylate, or a (meth)acrylate having a hydroxyl group, a carboxyl group, an amino group, or an epoxy group in addition to a (meth)acryloyl group.

[0065] The matrix may be, for example, a rubber such as acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, urethane rubber, silicone rubber, natural rubber, styrene butadiene rubber, styrene isoprene butadiene rubber, ethylene propylene diene rubber, chloroprene rubber, epoxidized natural rubber, or epoxidized butadiene rubber.

[0066] Next, a configuration for reducing resonance noise within the tire cavity S of the tire T using the resonance box 10 of the power generation device 1 will be described. The resonance box 10 has a second opening 14, which is covered by a piezoelectric film 20. This allows the resonance box 10 to function as a resonator. As shown in FIG. 1 , F is the frequency of tire cavity resonance noise, c is the speed of light, R is the radius of the cavity surface Ta of the tire T, r is the radius of the rim Ha of the wheel H mounted on the tire T, and π is the circular constant. In this case, the frequency of tire cavity resonance noise is calculated by F = c / ((R + r) × π). The resonance box 10 of the power generation device 1 preferably has a Helmholtz resonance structure that generates Helmholtz resonance with a resonance frequency within a range of ±100 Hz of the frequency of tire cavity resonance noise calculated from F = c / ((R + r) × π).

[0067] The Helmholtz resonance structure is a structure including components of a Helmholtz resonator that resonates with sound incident through an opening. In the power generation device 1, the Helmholtz resonance structure is formed by the resonance box 10. That is, in the resonance box 10, the non-air-permeable neck portion 15 connects the first opening 13 and the hollow portion 12. Therefore, the resonant frequency of the resonance box 10, which functions as a Helmholtz resonator, varies depending on the extension length of the neck portion 15, the inner diameter of the first opening 13, and the like. For example, the longer the extension length of the neck portion 15, the lower the resonant frequency. Furthermore, the smaller the inner diameter of the first opening 13, the lower the resonant frequency. For this reason, it is preferable that these conditions of the resonance box 10 be adjusted so that Helmholtz resonance occurs at a resonant frequency within a range of ±100 Hz of the frequency of tire cavity resonance sound calculated from F = c / ((R + r) × π).

[0068] In this way, by providing a Helmholtz resonance structure that generates Helmholtz resonance at a resonance frequency within a range of ±100 Hz of the frequency of tire cavity resonance noise, tire cavity resonance noise can be reduced.

[0069] 7 is a diagram illustrating a method for calculating the resonant frequency of the Helmholtz resonance structure. The resonant frequency of the Helmholtz resonance structure, which resonates with the sound incident from the first opening 13, can be adjusted from various dimensions of the hollow portion 12 according to this calculation method.

[0070] In Figure 7, V is the volume of the hollow portion 12. If a neck portion 15 extends into the hollow portion 12, the volume obtained by subtracting the volume of the neck portion 15 is defined as V. α is the area of ​​the first opening 13 when viewed from the thickness direction of the outer wall 11. δ is an opening end correction; for example, if the shape of the first opening 13 is circular, δ can be calculated as 0.8 times the diameter of the first opening 13. If the shape of the first opening 13 is not circular, δ can be calculated as 0.8 times the diameter of a perfect circle having the same area as the area of ​​the first opening 13. L is the depth of the first opening 13, i.e., the extension length of the neck portion 15 (hollow portion).

[0071] In this way, the resonance box 10 can absorb sound by Helmholtz resonance. Furthermore, when Helmholtz resonance occurs in the resonance box 10, the air in the hollow portion 12 also vibrates in a resonant manner. A piezoelectric film 20 is attached to the resonance box 10 so as to cover the second opening 14. Therefore, the piezoelectric film 20 vibrates due to the resonant vibration of the air in the hollow portion 12. In this way, the power generation device 1 can absorb sound by using Helmholtz resonance, and can generate power by vibrating the piezoelectric film 20 due to the resonant vibration of the air when absorbing sound.

[0072] 1 is operated by power generated by the piezoelectric film 20 of the power generation device 1. The transmitter 2 transmits electromotive force information of the power generation device 1 (piezoelectric film 20) to the determination device 3. The transmitter 2 is configured as an ECU (Electronic Control Unit) including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a communication module. The transmitter 2 realizes various functions by, for example, loading a program recorded in the ROM into the RAM and executing the program loaded into the RAM with the CPU.

[0073] The transmitting device 2 functionally has an information generating unit 2a and a transmitting unit 2b. The information generating unit 2a generates electromotive force information to be transmitted to the determining device 3. The electromotive force information includes the magnitude of the electromotive force generated in the piezoelectric film 20. The information generating unit 2a can generate the electromotive force information by measuring the electromotive force generated in the piezoelectric film 20 of the power generating device 1. The magnitude of the electromotive force included in the electromotive force information may be represented by an electromotive force waveform.

[0074] The transmitter 2b transmits the electromotive force information generated by the information generator 2a to the determination device 3. The transmitter 2b can transmit the electromotive force information to the determination device 3 provided outside the cavity S of the tire T by wireless communication.

[0075] Here, the electromotive forces generated by the two power generating devices 1 provided in the cavity S of the tire T will be described. FIG. 8 is a schematic diagram showing the distribution of sound pressure within the cavity of the tire. As shown in FIG. 8, vibrations caused by unevenness of the road surface W are input to the tire T from the portion in contact with the road surface W. The portion of the tire T in contact with the road surface W is the vibration position that is affected by the unevenness of the road surface W and is vibrated. When vibrations are generated due to the influence of the unevenness of the road surface W, a sound pressure distribution occurs within the cavity S of the tire T with a certain regularity.

[0076] Here, within the cavity S of the tire T, the sound pressure is high at the excitation position and at a position opposite the excitation position across the center position of the tire T. That is, in the example shown in Fig. 8, the sound pressure is high in a lower portion (excitation position) and an upper portion (a position opposite the excitation position across the center position of the tire T) within the cavity S of the tire T. Furthermore, the sound pressure is low at a position shifted by 90° in the rotation direction of the tire T from the portion where the sound pressure is high. That is, in the example shown in Fig. 8, the sound pressure is low within the cavity S of the tire T at the right portion and the left portion in Fig. 8.

[0077] In this embodiment, the mounting positions of the two power generators 1 on the lumen surface Ta of the tire T are offset by 90° in the rotational direction of the tire T. Therefore, when the tire T is affected by unevenness in the road surface W, the two power generators 1 can be located in areas with sound pressure distributions that tend to differ from each other. For example, when vibration is input to the tire T, one power generator 1 can be located in an area with high sound pressure, and the other power generator 1 can be located in an area with low sound pressure.

[0078] Furthermore, there is a correlation between the electromotive force generated by the power generation device 1 and the sound pressure generated in the cavity S of the tire T. As the sound pressure increases, the electromotive force generated by the power generation device 1 also increases.

[0079] Here, we will explain the differences in the electromotive force waveforms of the two power generators 1 (piezoelectric films 20) when the relative positions of the two power generators 1 with respect to the vibration position of the tire T are different. FIGS. 9( a) to 9(c) are schematic diagrams showing the relative positions of the two power generators 1 with respect to the vibration position of the tire. For convenience of explanation, one of the two power generators 1 may be referred to as the first power generator 1A and the other as the second power generator 1B. In FIGS. 9( a) to 9(c), the first power generator 1A is indicated by a circle, and the second power generator 1B is indicated by a triangle. In FIGS. 9( a) to 9(c), the position at which vibration is generated due to the influence of unevenness in the road surface W is indicated as vibration position K. The tire T rotates in the order of the first power generator 1A and the second power generator 1B, with the first power generator 1A and the second power generator 1B approaching the road surface W.

[0080] In Figure 9(a), it is assumed that a small protrusion is traveled over when the tire T is in the rotating state shown in this figure. In Figure 9(b), it is assumed that a small protrusion is traveled over when the tire T is in the rotating state shown in this figure. In other words, Figures 9(a) to 9(c) show states in which the positions of the two power generation devices 1 are different from each other when small protrusions of the same shape are traveled over.

[0081] In the state shown in FIG. 9( a), the first power generating unit 1A is offset by 90° from the vibration position K of the tire T in the opposite direction to the rotational direction of the tire T. The second power generating unit 1B is offset by 90° from the first power generating unit 1A in the opposite direction to the rotational direction of the tire T. In other words, the second power generating unit 1B faces the vibration position K across the center of rotation of the tire T. This rotational state of the tire T is referred to as a first rotational state. Suppose the tire T runs over a small protrusion while in the first rotational state. When the tire T runs over the small protrusion, vibrations are generated in the tire T at the vibration position K due to the influence of the protrusion. This changes the sound pressure within the inner cavity S of the tire T, causing the piezoelectric films 20 of the first power generating unit 1A and the second power generating unit 1B to vibrate. Then, an electromotive force due to the protrusion is generated in the piezoelectric films 20 of the first power generating unit 1A and the second power generating unit 1B.

[0082] Fig. 10(a) is a graph showing the electromotive force waveform of the first power generator at each rotation state of the tire. Fig. 10(b) is a graph showing the electromotive force waveform of the second power generator at each rotation state of the tire. As shown by the solid lines in Fig. 10(a) and Fig. 10(b), when the tire rides over a small protrusion in the first rotation state, an electromotive force having a peak greater than that of the first power generator 1A is generated in the second power generator 1B.

[0083] In the state shown in FIG. 9( b), the first power generating unit 1A is shifted by 45° in the opposite direction to the rotational direction of the tire T from the vibration position K of the tire T. The second power generating unit 1B is shifted by 90° in the opposite direction to the rotational direction of the tire T from the first power generating unit 1A. This rotational state of the tire T is referred to as a second rotational state. Suppose that the tire T runs over a small protrusion in the second rotational state. As a result, an electromotive force due to the protrusion is generated in each of the piezoelectric films 20 of the first power generating unit 1A and the second power generating unit 1B. As shown by the dashed lines in FIGS. 10( a) and 10(b), when the tire T runs over a small protrusion in the second rotational state, an electromotive force with a peak at the same level is generated in the first power generating unit 1A and the second power generating unit 1B.

[0084] In the state shown in FIG. 9( c), the first power generating unit 1A is located at vibration position K of the tire T. The second power generating unit 1B is shifted 90° from the first power generating unit 1A in the opposite direction to the rotational direction of the tire T. This rotational state of the tire T is referred to as a third rotational state. Suppose that the tire T runs over a small protrusion in the third rotational state. As a result, an electromotive force due to the protrusion is generated in the piezoelectric films 20 of the first power generating unit 1A and the second power generating unit 1B. As shown by the dashed dotted lines in FIGS. 10( a) and 10(b), when the tire T runs over a small protrusion in the third rotational state, an electromotive force having a larger peak is generated in the first power generating unit 1A than in the second power generating unit 1B.

[0085] In this way, the electromotive force generated in each power generation device 1 differs depending on the relative position between the two power generation devices 1 and the vibration position K where vibration occurs due to riding over a protrusion or the like. Two transmitting devices 2 provided for the two power generation devices 1 respectively transmit electromotive force information of each power generation device 1, including the magnitude of such electromotive force, to the determining device 3.

[0086] 1 determines the unevenness of the road surface on which the tire T rolls based on the electromotive force information acquired from the transmitter. The determination device 3 is configured by an ECU similar to that of the transmitter 2.

[0087] The determination device 3 functionally includes a receiving unit 3a and a determining unit 3b. The receiving unit 3a receives electromotive force information transmitted by the transmitting unit 2b of the transmitting device 2. The determining unit 3b determines the unevenness of the road surface based on the received electromotive force information. As an example, the determining unit 3b converts the electromotive force obtained based on the electromotive force information into sound pressure, and determines the unevenness of the road surface based on the obtained sound pressure. Here, as described above, there is a correlation between the electromotive force included in the electromotive force information and the sound pressure generated in the inner cavity S of the tire T. Furthermore, this correlation also depends on the device designs of the power generation device 1 and the transmitting device 2. The determining unit 3b can convert the electromotive force into sound pressure based on this correlation.

[0088] The determination unit 3b estimates the sound pressure at each of the positions of the first power generating unit 1A and the second power generating unit 1B from the electromotive forces generated by the first power generating unit 1A and the second power generating unit 1B. The determination unit 3b calculates the average value of the estimated sound pressure at the position of the first power generating unit 1A and the sound pressure at the position of the second power generating unit 1B as the average sound pressure inside the cavity S of the tire T. Fig. 11 is a graph showing changes in the average sound pressure obtained by averaging the sound pressure at the position of the first power generating unit and the sound pressure at the position of the second power generating unit.

[0089] As described above, the mounting positions of the first power generating unit 1A and the second power generating unit 1B are offset by 90° in the rotational direction of the tire T. Therefore, when the tire T is affected by unevenness in the road surface W, the first power generating unit 1A and the second power generating unit 1B can be located in portions of the sound pressure distribution that tend to be different from each other. This makes it possible to keep the average sound pressure calculated when a protrusion is traveled over, constant regardless of the rotational state of the tire T at the time the protrusion is traveled over. In other words, the waveform of the average sound pressure when a protrusion is traveled over in the first rotational state shown in FIG. 9( a), the waveform of the average sound pressure when a protrusion is traveled over in the second rotational state shown in FIG. 9( b), and the waveform of the average sound pressure when a protrusion is traveled over in the third rotational state shown in FIG. 9( c) are all the same.

[0090] The determination unit 3b determines the magnitude of road surface unevenness based on the magnitude of the electromotive force included in the electromotive force information acquired from the transmission device 2. Specifically, the determination unit 3b can determine the magnitude of road surface unevenness based on the calculated magnitude of the average sound pressure of the first power generation unit 1A and the second power generation unit 1B. Here, there is a correlation between the magnitude of sound pressure inside the lumen S of the tire T and the magnitude of road surface unevenness. For example, as the magnitude of road surface unevenness increases, the sound pressure generated inside the lumen S of the tire T increases. This correlation between the magnitude of sound pressure and the magnitude of road surface unevenness may be set in advance, for example, by examining an actual correlation.

[0091] Fig. 12 is a diagram showing changes in average sound pressure when a tire goes over protrusions of different sizes. In Fig. 12, the peak height of the first average sound pressure waveform N1 is lower than the peak height of the second average sound pressure waveform. For example, if the calculated average sound pressure waveform is the first average sound pressure waveform N1 shown in Fig. 12, the determination unit 3b determines that the road surface unevenness is small. For example, if the calculated average sound pressure waveform is the second average sound pressure waveform N2 shown in Fig. 12, the determination unit 3b determines that the road surface unevenness is large.

[0092] Furthermore, the determination unit 3b determines the interval between unevennesses on the road surface (the period of unevenness) based on the period of change in electromotive force included in the electromotive force information acquired from the transmission device 2. Specifically, the determination unit 3b can determine the interval between unevennesses on the road surface based on the period of change in the calculated average sound pressure of the first power generation unit 1A and the second power generation unit 1B. Here, there is a correlation between the period of change in sound pressure inside the lumen S of the tire T and the interval between unevennesses on the road surface. For example, as the period of change in sound pressure inside the lumen S of the tire T (e.g., the interval between peaks) becomes shorter, the interval between unevennesses on the road surface also becomes narrower.

[0093] The period of change in sound pressure inside the cavity S of the tire T also correlates with the vehicle speed. The period of change in sound pressure inside the cavity S of the tire T becomes shorter as the vehicle speed increases. The determination unit 3b can acquire vehicle speed data from a vehicle control device, a vehicle speed sensor, etc. The determination unit 3b can determine the interval between unevennesses on the road surface based on the calculated period of change in average sound pressure inside the cavity S of the tire T and the acquired vehicle speed data.

[0094] FIG. 13 is a diagram showing changes in the waveform of the average sound pressure calculated by the determination device. Assume that the vehicle speed is constant when the average sound pressure shown in FIG. 13 is calculated. In FIG. 13, the peak interval of the waveform in region M1 of the average sound pressure waveform is wider than the peak interval of the waveform in region M2. If the change in the waveform of the calculated average sound pressure is the waveform of region M1 shown in FIG. 13, the determination unit 3b determines that the intervals between the irregularities in the road surface are wide. For example, if the change in the waveform of the calculated average sound pressure is the waveform of region M2 shown in FIG. 13, the determination unit 3b determines that the intervals between the irregularities in the road surface are narrow.

[0095] As described above, there is a correlation between the unevenness of the road surface and the average sound pressure inside the lumen S of the tire T. For this reason, data on the average sound pressure for each road surface unevenness is investigated in advance. Then, the unevenness of each road surface and the data on the average sound pressure are associated and stored as road surface data. The determination unit 3b can determine the unevenness of the road surface by applying the average sound pressure calculated based on the electromotive force information to the road surface data stored in advance. For example, the unevenness of the road surface may include various road surface conditions such as a damaged road surface, a snow-covered road, and an unpaved road surface.

[0096] The road surface unevenness state determined by the determination device 3 may be provided to a road surface manager or used in a tire usage history to determine the appropriate time to replace tires. The determined road surface unevenness state may also be used to control the vehicle (control of acceleration / deceleration, control of suspension damping force, etc.) in accordance with the road surface unevenness state.

[0097] Next, a description will be given of the flow of the process for determining the unevenness of a road surface, which is performed in the road surface condition determination system 100. Fig. 14 is a flowchart showing the flow of the process for determining the unevenness of a road surface, which is performed in the road surface condition determination system. The process shown in Fig. 14 starts from the start a predetermined time after the process reaches the end.

[0098] 14, the information generating unit 2a of the transmitting device 2 measures the electromotive force of the piezoelectric film 20 of the power generating device 1. The information generating unit 2a generates electromotive force information including the magnitude of the measured electromotive force (S101). The transmitting unit 2b transmits the electromotive force information generated by the information generating unit 2a to the determining device 3. The receiving unit 3a of the determining device 3 receives the electromotive force information transmitted from the transmitting device 2 (S102).

[0099] The determination unit 3b of the determination device 3 converts the electromotive force into sound pressure based on the received electromotive force information (S103). Here, the determination unit 3b converts the electromotive forces of the two power generators 1 into sound pressures. The determination unit 3b averages the converted sound pressures of the two power generators 1 to calculate an average sound pressure (S104). The determination unit 3b determines the unevenness of the road surface based on the calculated average sound pressure (S105).

[0100] The transmitter 2 provided in the cavity S of the tire T is operated by power generated by the power generator 1 provided in the cavity S of the tire T. A tire power generation method in which power is generated by the power generator 1 of the road surface condition determination system 100 will be described below. FIG. 15 is a flowchart showing the flow of the tire power generation method. The power generator 1 is disposed in the cavity S of the tire T. In this embodiment, the power generator 1 is attached to the cavity surface Ta of the tire T. The tire power generation method is a method of generating power by rotating the tire T provided with the power generator 1. The series of steps shown in FIG. 15 are repeatedly and continuously performed to generate power continuously.

[0101] As shown in Fig. 15 , a vehicle equipped with a tire T to which a power generating device 1 is attached is driven to rotate the tire T (S201: step of rotating the tire). As the tire T rotates, sound pressure changes within the cavity S of the tire T due to the influence of unevenness on the road surface. The power generating device 1 introduces air vibrations within the cavity S of the tire T into the resonance box 10, and the air vibrations generated by resonance with the resonance box 10 vibrate the piezoelectric film 20, generating electricity via the piezoelectric film 20 (S202: step of generating electricity via the piezoelectric film). The power generated by the piezoelectric film 20 of the power generating device 1 is extracted from the power generating device 1 and used to operate the transmission device 2. The power extracted from the power generating device 1 may also be used for devices other than the transmission device 2.

[0102] As described above, the power generating device 1 generates power by rotating the tire T. The power generating method for a tire includes the steps of rotating the tire T having the power generating device 1 disposed in the inner cavity S, and introducing air vibrations in the inner cavity S of the tire T into the resonance box 10, causing the piezoelectric film 20 of the power generating device 1 to vibrate due to the air vibrations generated when resonating with the resonance box 10, and generating power using the piezoelectric film 20. In this way, with this power generating method for a tire, the piezoelectric film 20 can be vibrated by the air vibrations in the inner cavity S generated by rotating the tire T.

[0103] Here, sound pressure is high inside the cavity S of the tire T. Furthermore, because the cavity S of the tire T is sealed, acoustic energy is not diffracted or diffused. Therefore, in this power generation method for a tire, the piezoelectric film 20 can be efficiently vibrated by air vibrations inside the cavity S of the tire T. In this way, in this power generation method for a tire, power can be generated more efficiently as the tire T rotates.

[0104] The power generation device 1 includes an outer wall 11, a hollow portion 12 formed within the outer wall 11, and a resonance box 10 having a first opening 13 and a second opening 14 for introducing air vibrations into the hollow portion. The second opening 14 of the resonance box 10 is covered with a piezoelectric film 20. Therefore, in the power generation device 1, air vibrations are introduced into the hollow portion 12 from the first opening 13, allowing the resonance box 10 to function as a Helmholtz resonance sound absorber. The power generation device 1 can vibrate the piezoelectric film 20 provided at the second opening 14 of the resonance box 10 by the air vibrations generated when the resonance box 10 resonates. In this way, the power generation device 1 can generate electricity more efficiently as the tire T rotates, and can reduce resonance noise within the cavity S of the tire T.

[0105] In the power generation device 1, the resonance box 10 includes a hollow neck portion 15 that connects the first opening 13 and the hollow portion 12. Therefore, in the power generation device 1, the resonant frequency of Helmholtz resonance can be adjusted by adjusting the length of the neck portion 15. In addition, in the power generation device 1, by lengthening the neck portion 15, Helmholtz resonance with a resonant frequency in the low-frequency range can be generated, and therefore low-frequency resonance noise such as tire cavity resonance noise can be reduced.

[0106] In the power generation device 1, at least a portion of the neck portion 15 is arranged within the outer wall 11, so that the neck portion 15 can be lengthened to generate Helmholtz resonance with a resonant frequency in the low frequency range, while the power generation device 1 can be made smaller.

[0107] In the power generating device 1, the end of the hollow portion 12 at the neck portion 15 opens toward the piezoelectric film 20. This allows the resonant vibration of the air generated in the neck portion 15 to be efficiently applied to the piezoelectric film 20 via the air in the hollow portion 12.

[0108] In the power generation device 1, the neck portion 15 is arranged on the bottom wall portion 11a of the outer wall 11 so as to extend along the bottom wall portion 11a, thereby suppressing movement of the neck portion 15 due to centrifugal force when the tire T rotates.

[0109] In the power generation device 1, the resonance box 10 is configured to be long in the first direction D1, and the first opening 13 is formed at the end of the outer wall 11 in the first direction D1, so that the neck portion 15 can be lengthened while the resonance box 10 is made smaller.

[0110] In the power generation device 1, the first opening 13 and the second opening 14 are provided at both ends in the longitudinal direction (first direction D1) of the resonance box 10. Therefore, in this power generation device 1, the neck portion 15 disposed between the first opening 13 and the second opening 14 can be made longer while the resonance box 10 is made smaller.

[0111] In the power generating device 1, the top wall portion 11b of the outer wall 11 is convexly curved, which makes it easier to receive forces directed toward the bottom wall portion 11a. This makes it possible to prevent the resonance box 10 of the power generating device 1 from being deformed by centrifugal force generated when a vehicle having the power generating device 1 attached to the inner cavity surface Ta of the tire T is driven at high speed. Furthermore, in this power generating device 1, because deformation of the resonance box 10 is prevented, deformation of the piezoelectric film 20 attached to the resonance box 10 is also prevented. As a result, in this power generating device 1, deformation of the resonance box 10 is prevented, allowing the piezoelectric film 20 to vibrate more appropriately and preventing a decrease in power generation efficiency due to the piezoelectric film 20.

[0112] In the power generating device 1, the top wall portion 11b is formed in an arc shape in a cross section perpendicular to the first direction D1, and therefore deformation of the top wall portion 11b due to centrifugal force can be effectively suppressed.

[0113] In the power generation device 1, the outer wall 11 has at least one of a Shore A hardness of 40 or more and 100 or less and a Shore D hardness of 10 or more and 70 or less, thereby suppressing deformation of the resonance box 10 due to centrifugal force while improving its conformability to the inner cavity surface Ta of the tire T.

[0114] In the power generating device 1, the outer wall 11 has an elastomer, so that deformation of the resonance box 10 due to centrifugal force can be suppressed while the ability to follow the inner cavity surface Ta of the tire T can be improved.

[0115] The road surface condition determination system 100 comprises the above-mentioned power generation device 1, a determination device 3 that determines the unevenness of the road surface, and a transmission device 2 that transmits electromotive force information including the magnitude of the electromotive force generated in the piezoelectric film 20 of the power generation device 1 to the determination device 3.

[0116] When the tire T rolls on an uneven road surface, air vibrations occur in the lumen S of the tire T due to the influence of the road surface unevenness. In other words, there is a correlation between the air vibrations generated in the lumen S of the tire T and the unevenness of the road surface. Therefore, the determination device 3 of the road surface condition determination system 100 can determine the unevenness of the road surface by using the electromotive force information of the piezoelectric film 20 of the power generation device 1 as information regarding the air vibrations in the lumen S of the tire T. The determination device 3 determines the magnitude of the road surface unevenness based on the magnitude of the electromotive force included in the electromotive force information, or determines the interval between the road surface unevenness based on the period of change in the electromotive force. This allows the determination device 3 to more appropriately determine the unevenness of the road surface. In this way, the power generation device 1 has a power generation function and also functions as a sensor that detects information for determining the unevenness of the road surface.

[0117] Furthermore, as described above, the power generating device 1 in the road surface condition determination system 100 can generate electricity more efficiently as the tire T rotates. This allows the road surface condition determination system 100 to operate the transmitting device 2 using the power generated by the power generating device 1 and stably transmit electromotive force information to the determination device 3. In this way, the road surface condition determination system 100 can determine the unevenness of the road surface while generating electricity more efficiently as the tire T rotates.

[0118] (First Modified Example of Power Generator) Below, a modified example of the power generator provided in the road surface condition determination system 100 will be described. A power generator 1C according to the first modified example will be described with reference to FIG. 16 . The power generator 1C according to the first modified example is basically the same as the power generator 1 according to the embodiment, and differs from the power generator 1 according to the embodiment only in that it further includes a flange portion. Therefore, below, only the differences from the power generator 1 according to the embodiment will be described, and a description of the same aspects as the power generator 1 according to the embodiment will be omitted.

[0119] 16 is a schematic cross-sectional view of a power generator according to a first modification. As shown in FIG. 16, the power generator 1C according to the first modification further includes a flange portion 16.

[0120] The flange portion 16 is a portion that forms part of the mounting surface 10a. The flange portion 16 extends from the bottom wall portion 11a toward the outside of the resonance box 10. Specifically, the flange portion 16 extends along the mounting surface 10a so as to widen from the bottom wall portion 11a of the outer wall 11 of the resonance box 10. The width of the flange portion 16 is, for example, approximately 1 mm or more and 20 mm or less. The width of the flange portion 16 is the dimension in the direction away from the bottom wall portion 11a.

[0121] As described above, the power generator 1C according to the first modified example includes the flange portion 16 extending from the bottom wall portion 11a toward the outside of the resonance box 10, and therefore the flange portion 16 can be pressed against the lumen surface Ta of the tire T. This makes it possible to easily attach the power generator 1C to the lumen surface Ta of the tire T.

[0122] (Second Modification of Power Generator) A power generator 1D according to a second modification will be described with reference to Figures 17 to 19. The power generator 1D according to the second modification is basically the same as the power generator 1 according to the embodiment, and differs from the power generator 1 according to the embodiment only in that the resonance box further includes a support portion. For this reason, only the differences from the power generator 1 according to the embodiment will be described below, and a description of the same aspects as the power generator 1 according to the embodiment will be omitted.

[0123] Fig. 17 is a schematic cross-sectional view of a power generation device according to a second modification. Fig. 18 is a schematic cross-sectional view taken along line XVIII-XVIII in Fig. 17. Fig. 19 is a schematic cross-sectional view taken along line XIX-XIX in Fig. 17. Note that Fig. 17 is a cross-sectional view corresponding to Fig. 5, and is also a schematic cross-sectional view taken along line XVII-XVII in Figs. 18 and 19. As shown in Figs. 17 to 19, a resonance box 10D of a power generation device 1D according to a second modification includes an outer wall 11, a hollow portion 12, a first opening 13, a second opening 14, a neck portion 15, and a support portion 17.

[0124] The support portion 17 is a portion for supporting the top wall portion 11b relative to the bottom wall portion 11a. The support portion 17 extends from the bottom wall portion 11a side to the top wall portion 11b side in the hollow portion 12. Specifically, the support portion 17 is configured as a plate-shaped rib and extends in the third direction D3 from the neck portion 15 to the top wall portion 11b. That is, the support portion 17 supports the top wall portion 11b relative to the bottom wall portion 11a via the neck portion 15. The support portion 17 has a shape that allows the hollow portion 12 to maintain a single space. For example, the support portion 17 has a shape in which a portion between the neck portion 15 and the piezoelectric film 20 is cut out. The support portion 17 may support the top wall portion 11b only in a portion of the first direction D1, or may support the top wall portion 11b over the entire first direction D1. For example, the support portion 17 may be connected to the top wall portion 11b over the entire area in the first direction D1 so as to support the top wall portion 11b over the entire area in the first direction D1.

[0125] As described above, in the power generation device 1D of the second modified example, the resonance box 10D is provided with a support portion 17 that supports the top wall portion 11b against the bottom wall portion 11a, thereby further suppressing deformation of the top wall portion 11b due to centrifugal force.

[0126] In addition, in this power generation device 1D, the support portion 17 extends from the bottom wall portion 11a side to the top wall portion 11b side in the hollow portion 12, so that the power generation device 1D can be made smaller while suppressing deformation of the top wall portion 11b due to centrifugal force.

[0127] (Third Modification of Power Generator) A power generator 1E according to a third modification will be described with reference to Figures 20 and 21. The power generator 1E according to the third modification is basically the same as the power generator 1 according to the embodiment, and differs from the power generator 1 according to the embodiment only in that it includes a plurality of resonance boxes. Therefore, only differences from the power generator 1 according to the embodiment will be described below, and descriptions of similarities between the power generator 1 according to the embodiment will be omitted.

[0128] Fig. 20 is a schematic perspective view of a power generating device according to a third modified example. Fig. 21 is a schematic cross-sectional view taken along line XXI-XXI shown in Fig. 20. As shown in Figs. 20 and 21, a power generating device 1E according to the third modified example includes a plurality of resonance boxes 10, piezoelectric films 20 attached to each resonance box 10, and a connecting wall 30.

[0129] The connecting walls 30 are portions that connect multiple resonance boxes 10. The connecting walls 30 connect multiple resonance boxes 10, for example, so that the multiple resonance boxes 10 are arranged in the second direction D2. The thickness, Shore A hardness, Shore D hardness, material, etc. of the connecting walls 30 can be the same as those of the resonance boxes 10. The connecting walls 30 include connecting wall portions 30a arranged between adjacent resonance boxes 10 and flange wall portions 30b arranged around the multiple resonance boxes 10. The number of resonance boxes 10 connected by the connecting walls 30 is not particularly limited, but can be, for example, 1 to 10. The distance between adjacent resonance boxes 10 is, for example, approximately 2 mm to 10 mm.

[0130] As described above, the power generating device 1E according to the third modification can improve the sound absorption performance of the power generating device 1E by including a plurality of resonance boxes 10. Furthermore, the power generating device 1E can improve the power generation performance of the power generating device 1E by including a plurality of piezoelectric films 20.

[0131] Furthermore, in this power generating device 1E, adjacent resonance boxes 10 are spaced apart by connecting walls 30 that connect multiple resonance boxes 10, so that the connecting wall portions 30a can be pressed against the lumen surface Ta of the tire T. This makes it possible to easily attach the power generating device 1E to the lumen surface Ta of the tire T.

[0132] Furthermore, in this power generating device 1E, the flange wall portions 30b are arranged around the multiple resonance boxes 10, so that the flange wall portions 30b can be pressed against the lumen surface Ta of the tire T. This makes it possible to easily attach the power generating device 1E to the lumen surface Ta of the tire T.

[0133] The present disclosure is not limited to the above-described embodiments, and modifications can be made as appropriate without departing from the spirit of the present disclosure.

[0134] For example, as shown in FIG. 6 , the top wall portion 11b according to the embodiment has a shape that follows an arc of approximately half the circumference of a circle when viewed along the first direction D1. However, the present invention is not limited to this. The top wall portion may have a shape that follows an arc of more than half the circumference of a circle when viewed along the first direction D1. In other words, the tubular shape formed by the top wall portion and the bottom wall portion may be closer to a cylindrical shape than the tubular shape formed by the top wall portion 11b and the bottom wall portion 11a shown in FIG. 6 , or may be an approximately cylindrical shape. In this way, the top wall portion and the bottom wall portion may have an approximately cylindrical shape that forms a hollow portion inside.

[0135] For example, the mounting surface of each of the above-described power generating devices may be formed in a flat shape or a curved shape. The mounting surface of each of the power generating devices may be formed in an arc-shaped curved shape that conforms to the inner surface of the tire. In this way, the mounting surface is curved in an arc-shaped shape, which improves ease of mounting to the inner surface of the tire.

[0136] Furthermore, for example, the shape of the outer wall of the resonance box, the position of the first opening, the position of the second opening, the position of the neck portion, the shape of the support portion, etc. are not particularly limited and can be modified in various ways.

[0137] The road surface condition determination system is not limited to having two power generators. FIG. 22 is a schematic cross-sectional view of a tire equipped with a power generator of a road surface condition determination system according to a modified example. As shown in FIG. 22 , the road surface condition determination system according to the modified example includes four power generators 1. The four power generators 1 are arranged at equal intervals in the circumferential direction on the lumen surface Ta of the tire T. That is, the four power generators 1 are arranged at 90° intervals in the circumferential direction of the tire T. Even in this case, in the road surface condition determination system, two adjacent power generators 1 can be located in parts of the sound pressure distribution that tend to differ from each other when the tire T is affected by unevenness in the road surface W. As a result, the road surface condition determination system according to the modified example can determine the unevenness of the road surface based on the electromotive force information of these power generators 1, similar to the road surface condition determination system 100 according to the embodiment. Note that the road surface condition determination system is not limited to having two or four power generators 1 as shown in FIGS. 2 and 22 . The road surface condition determination system may include a number of power generators 1 other than two or four.

[0138] In each of the power generating devices described above, the position at which the piezoelectric film 20 is provided is not limited to the position on the opposite side of the first opening 13 in the first direction D1. The piezoelectric film 20 may be provided at any appropriate position on the resonance box. For example, the piezoelectric film 20 may be provided on the top wall portion of the outer wall.

[0139] The gist of the present disclosure is as follows: [1] to

[16] . [1] A tire power generation method for generating electricity by rotating a tire, comprising: rotating the tire having a tire power generation device disposed within the tire cavity; introducing air vibrations within the tire cavity into a resonance box of the tire power generation device, causing a piezoelectric film provided on the tire power generation device to vibrate due to the air vibrations generated by resonance with the resonance box, and generating electricity using the piezoelectric film. [2] A tire power generation device disposed within the tire cavity, used in the tire power generation method described in [1] above, comprising: a resonance box having an outer wall, a hollow portion formed in the outer wall, a first opening that opens the hollow portion to the outside of the outer wall and introduces the air vibrations into the hollow portion, and a second opening that opens the hollow portion to the outside of the outer wall; and a piezoelectric film attached to the resonance box so as to cover the second opening. [3] The tire generator according to [2] above, wherein the resonance box includes a hollow neck portion that communicates with the first opening and the hollow portion. [4] The tire generator according to [3] above, wherein at least a portion of the neck portion is disposed within the outer wall. [5] The tire generator according to [3] or [4] above, wherein the end of the neck portion on the hollow portion side is open toward the piezoelectric film. [6] The tire generator according to any one of [3] to [5] above, wherein the outer wall includes a bottom wall portion attached to the inner surface of the tire and a top wall portion that forms the hollow portion between itself and the bottom wall portion, and the neck portion is disposed on the bottom wall portion so as to extend along the bottom wall portion. [7] The tire generator according to any one of [3] to [6] above, wherein the resonance box is configured to be elongated in a first direction, and the first opening is formed at the end of the outer wall in the first direction. [8] The tire generator according to [7] above, wherein the second opening is formed at an end of the outer wall opposite to the first opening in the first direction. [9] The tire generator according to [7] above or [8] above, wherein the outer wall includes a bottom wall portion attached to an inner cavity surface of the tire and a top wall portion forming the hollow portion between the bottom wall portion and the top wall portion, and the top wall portion is convexly curved.

[10] The tire generator according to [9] above, wherein the top wall portion is formed in an arc shape in a cross section perpendicular to the first direction.

[11] The tire generator according to [9] or

[10] above, wherein the resonance box includes a support portion that supports the top wall portion against the bottom wall portion.

[12] The tire generator according to

[11] above, wherein the support portion extends from the bottom wall portion side to the top wall portion side in the hollow portion.

[13] The tire generator according to any one of [9] to

[12] above, further including a flange portion extending from the bottom wall portion toward the outside of the resonance box.

[14] The tire generator according to any one of [2] to

[13] above, wherein the outer wall has at least one of a Shore A hardness of 40 to 100 and a Shore D hardness of 10 to 70.

[15] The tire generator according to any one of [2] to

[14] above, wherein the outer wall includes an elastomer.

[16] The tire generator according to any one of [2] to

[15] above, wherein the outer wall comprises a bottom wall attached to an inner cavity surface of the tire and a top wall forming the hollow between the bottom wall and the top wall, and the bottom wall and the top wall have a substantially cylindrical shape forming the hollow on the inside.

[17] A road surface condition determination system capable of determining the unevenness of a road surface on which a tire rolls, comprising: the tire generator according to any one of [2] to

[16] above; a determination device that determines the unevenness of the road surface; and a transmission device that transmits electromotive force information including a magnitude of an electromotive force generated in the piezoelectric film to the determination device, wherein the transmission device transmits the electromotive force information using power generated by the piezoelectric film, and the determination device determines the magnitude of the unevenness of the road surface based on the magnitude of the electromotive force included in the electromotive force information acquired from the transmission device, or determines the interval between the unevenness of the road surface based on a period of change in the electromotive force.

[0140] 1, 1C to 1E... power generation device (tire power generation device), 2... transmitter, 3... determination device, 10, 10D... resonance box, 11... outer wall, 11a... bottom wall portion, 11b... top wall portion, 12... hollow portion, 13... first opening, 14... second opening, 15... neck portion, 16... flange portion, 17... support portion, 20... piezoelectric film, 100... road surface condition determination system, S... inner cavity, T... tire, Ta... inner cavity surface.

Claims

1. A method for generating electricity by rotating a tire, comprising: rotating the tire having a tire-generating device disposed within its cavity; introducing air vibrations within the tire cavity into a resonance box of the tire-generating device, causing a piezoelectric film provided on the tire-generating device to vibrate due to the air vibrations resonating with the resonance box, and generating electricity using the piezoelectric film.

2. A generator for a tire disposed within the cavity of a tire, used in the power generation method for a tire as described in claim 1, comprising: an outer wall; a hollow portion formed within said outer wall; a resonance box having a first opening which opens said hollow portion to the outside of said outer wall and introduces air vibrations into said hollow portion; and a second opening which opens said hollow portion to the outside of said outer wall; and a piezoelectric film attached to said resonance box so as to cover said second opening.

3. The generator for a tire according to claim 2, wherein the resonance box has a hollow neck portion communicating with the first opening and the hollow portion.

4. The tire generator according to claim 3, wherein at least a portion of the neck portion is disposed within the outer wall.

5. The generator for a tire according to claim 3, wherein the end of the neck portion on the hollow portion side is open toward the piezoelectric film.

6. A tire power generation device as described in claim 3, wherein the outer wall comprises a bottom wall portion attached to the inner cavity surface of the tire and a top wall portion forming the hollow portion between the bottom wall portion and the top wall portion, and the neck portion is disposed on the bottom wall portion so as to extend along the bottom wall portion.

7. The generator for a tire according to claim 6, wherein the resonance box is configured to be long in a first direction, and the first opening is formed at an end of the outer wall in the first direction.

8. The tire generator according to claim 7, wherein the second opening is formed at an end of the outer wall opposite to the first opening in the first direction.

9. The tire generator according to claim 7, wherein the top wall portion is convexly curved.

10. The tire generator according to claim 9, wherein the top wall portion is formed in an arc shape in a cross section perpendicular to the first direction.

11. The generator for a tire according to claim 9, wherein the resonance box includes a support portion that supports the top wall portion against the bottom wall portion.

12. The tire generator according to claim 11, wherein the support portion extends from the bottom wall portion side to the top wall portion side in the hollow portion.

13. The tire power generation device according to claim 9, further comprising a flange portion extending from the bottom wall portion toward the outside of the resonance box.

14. The tire generator according to claim 2, wherein the outer wall has at least one of a Shore A hardness of 40 or greater and 100 or less and a Shore D hardness of 10 or greater and 70 or less.

15. The tire generator of claim 2, wherein the outer wall comprises an elastomer.

16. A road surface condition determination system capable of determining the unevenness of a road surface on which a tire is rolling, comprising: a tire power generating device according to any one of claims 2 to 15; a determination device for determining the unevenness of the road surface; and a transmission device for transmitting electromotive force information including a magnitude of electromotive force generated in the piezoelectric film to the determination device, wherein the transmission device transmits the electromotive force information using power generated by the piezoelectric film, and the determination device determines the magnitude of the unevenness of the road surface based on the magnitude of the electromotive force included in the electromotive force information obtained from the transmission device, or determines the interval between the unevenness of the road surface based on the period of change in the electromotive force.

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