Endless rotational body

Abstract

This endless rotational body comprises a rim part and a disk part located on the inner side of a ring of the rim part. A piezoelectric element is located at a position of the disk part where the stress during travel is higher than at other positions.

Description

Infinite rotating body 【0001】 The present disclosure relates to an infinite rotating body such as a tire wheel. 【0002】 There is a technique of arranging piezoelectric elements in tires, wheels, etc. For example, Patent Document 1 describes attaching a piezoelectric sensor to the outer peripheral surface of the rim portion of a wheel. Patent Document 2 describes providing a coating-type piezoelectric portion on the back surface of the grounding portion of a tire. 【0003】 Japanese Patent Application Laid-Open No. 2007-163230, Japanese Patent Application Laid-Open No. 2022-47625 【0004】 Although Patent Document 1 describes the idea of arranging a piezoelectric sensor on the outer peripheral surface of the rim portion, the outer peripheral surface of the rim portion of a wheel that has been put into practical use has a complex shape. Further technical consideration is required regarding at what position it is good to arrange a piezoelectric element in accordance with such a complex shape of the outer peripheral surface of the rim portion. 【0005】 The technique of Patent Document 2 generates electric power according to the strain generated on the grounding surface of the tire. Therefore, there is a risk that the piezoelectric portion arranged on the back surface of the grounding portion of the tire will be damaged while the tire is repeatedly deformed. 【0006】 In one aspect, an infinite rotating body is provided. The infinite rotating body includes a rim portion and a disk portion arranged inside the ring of the rim portion, and in the disk portion, a piezoelectric element is arranged at a position where the stress during running is higher than other positions. 【0007】Figure 1 is a perspective view of a passenger car wheel in the first embodiment, viewed from the outer surface in the vehicle width direction. Figure 2 is a perspective view of the passenger car wheel of Figure 1, viewed from the inner surface in the vehicle width direction. Figure 3 is a diagram showing the stress distribution on the outer surface in the vehicle width direction of the passenger car wheel of Figure 1. Figure 4 is a diagram showing the stress distribution on the inner surface in the vehicle width direction of the passenger car wheel of Figure 1. Figure 5 is a characteristic diagram showing the relationship between elapsed time and voltage when a piezoelectric element is placed at the position of the annular protrusion on the inner surface in the vehicle width direction. Figure 6 is a characteristic diagram showing the relationship between elapsed time and voltage when a piezoelectric element is placed between the decorative holes on the outer surface in the vehicle width direction. Figure 7 is a perspective view of a passenger car wheel in the second embodiment, viewed from the outer surface in the vehicle width direction. Figure 8 is a perspective view of the passenger car wheel of Figure 7, viewed from the inner surface in the vehicle width direction. Figure 9 is a diagram showing the stress distribution on the outer surface in the vehicle width direction of the passenger car wheel of Figure 7. Figure 10 is a diagram showing the stress distribution on the inner surface in the vehicle width direction of the passenger car wheel shown in Figure 7. Figure 11 is a perspective view of a modified passenger car wheel of the second embodiment, viewed from the outer surface. Figure 12 is a characteristic diagram showing the relationship between elapsed time and voltage when a piezoelectric element is placed on the outer surface between the holes and closer to the hub mounting portion than the disc flange portion. Figure 13 is a characteristic diagram showing the relationship between elapsed time and voltage when a piezoelectric element is placed on the inner surface along the outer circumference of the hub mounting portion. 【0008】 The wheel to which the infinitely rotating body according to this disclosure is applied will be described below with reference to the drawings. <First Embodiment> <Wheel Configuration> As shown in Figures 1 and 2, the vehicle wheel 10 according to the first embodiment is a wheel used in passenger cars and the like. This wheel 10 comprises a rim portion 11 and a disc portion 12. The rim portion 11 and the disc portion 12 are made of metal. The rim portion 11 and the disc portion 12 are made of a metal containing at least iron, or a metal containing at least aluminum. The vehicle wheel 10 is a wheel roll-formed or press-formed from a steel plate. The disc portion 12 is welded to the annular rim portion 11 to form the wheel 10. 【0009】The rim portion 11 comprises an inner flange portion 13, an inner bead seat portion 14, a drop portion 15, an outer bead seat portion 16, and an outer flange portion 17. In Figures 1 and 2, the inner side in the vehicle width direction, i.e., the side closer to the inside of the vehicle, is indicated as "in" when the wheel 10 is mounted on a vehicle, and the outer side in the vehicle width direction is indicated as "out". When the wheel 10 is mounted on a vehicle, the inner flange portion 13 and the inner bead seat portion 14 are located closer to the inside of the vehicle in the wheel axis direction than the outer bead seat portion 16 and the outer flange portion 17. In other words, when the wheel 10 is mounted on a vehicle, the outer bead seat portion 16 and the outer flange portion 17 are located closer to the outside of the vehicle in the wheel axis direction than the inner flange portion 13 and the inner bead seat portion 14. 【0010】 The disc portion 12 includes a hub hole 21, a hub mounting portion 22, a disc flange portion 23, a window portion forming portion 24, and a disc intermediate portion 25. The hub hole 21 is located in the center of the disc portion 12 in the disc radial direction (wheel radial direction). 【0011】 The hub mounting portion 22 is provided around the hub hole 21. The hub mounting portion 22 lies in a plane perpendicular to the disc axis direction (wheel axis direction). The hub mounting portion 22 is provided with a plurality of hub mounting bolt holes 22a. For example, four hub mounting bolt holes 22a are provided at equal intervals in the disc circumferential direction (wheel circumferential direction). However, the number of hub mounting bolt holes 22a is not limited to four; there may be three, five or more. Hub mounting bolts extending from the hub are inserted through the hub mounting bolt holes 22a. Hub nuts are then screwed onto the hub mounting bolts. In this way, the wheel 10 is fixed to the hub. 【0012】Multiple disc flange portions 23 are provided intermittently in the circumferential direction of the disc (four in this embodiment). The multiple disc flange portions 23 are on the same circumference. The disc flange portions 23 extend in a direction parallel to the disc axis direction at the radially outer end of the disc. The disc flange portions 23 fit with the rim portion 11 at the drop portion 15 of the rim portion 11 and are welded to the inner circumferential surface of the drop portion 15. The disc flange portions 23 may be welded to the rim portion 11 over the entire area of ​​the disc flange portion 23 in the circumferential direction of the disc, or they may be welded to the rim portion 11 only in a part including the central part of the disc circumferential direction of the disc flange portion 23. The disc portion 12 is fixed to the rim portion 11 by the disc flange portions 23. 【0013】 The window-forming portions 24 are provided between adjacent disc flange portions 23 in the circumferential direction of the disc. The same number of window-forming portions 24 are provided as the number of disc flange portions 23. The window-forming portions 24 are located radially inward of the disc compared to the disc flange portions 23. The window-forming portions 24 do not contact the rim portion 11, and form a window between them and the rim portion 11. The window-forming portions 24 are provided in the circumferential direction of the disc at positions corresponding to the hub mounting bolt holes 22a. Alternatively, the window-forming portions 24 may be provided in the circumferential direction of the disc at positions corresponding to the spaces between the hub mounting bolt holes 22a. 【0014】 The intermediate disc portion 25 is the disc portion that connects the hub mounting portion 22, the disc flange portion 23, and the window portion forming portion 24 in the radial direction of the disc. In the radial direction of the disc, the hub mounting portion 22 side of the intermediate disc portion 25 extends outward from the hub mounting portion 22 in both the radial direction and the axial direction of the disc. In the radial direction of the disc, the disc flange portion 23 side and the window portion forming portion 24 side of the intermediate disc portion 25 extend outward in both the radial direction and the axial direction of the disc. 【0015】The intermediate portion 25 of the disk has an annular projection 26 in the radially intermediate portion of the disk that is continuous in the circumferential direction of the disk and protrudes in the axial direction of the disk. In addition, the intermediate portion 25 of the disk has a plurality of decorative holes 27 that are provided at equal intervals in the circumferential direction of the disk. When both the annular projection 26 and decorative holes 27 are provided, the decorative holes 27 are provided radially outward from the annular projection 26. 【0016】 <Piezoelectric Element> Incidentally, in the wheel 10, the inner surface in the vehicle width direction is a surface that is difficult to see from the outside. In the annular projection 26, the inner surface in the vehicle width direction is the arrangement surface 29 on which the piezoelectric element 28, which serves as a power generation element, is positioned. The piezoelectric element 28 is positioned in a location within the disc portion 12 where the stress is higher than at other locations. 【0017】 Here, Figure 3 shows the stress distribution on the outer surface of the wheel 10 in the vehicle width direction when the vehicle load is applied to the wheel 10 from all sides. Figure 4 shows the stress distribution on the inner surface of the wheel 10 in the vehicle width direction when the vehicle load is applied to the wheel 10 from all sides. Darker colors indicate higher stress. 【0018】 In Figures 3 and 4, it can be seen that the stress at the location of the annular projection 26 within the disk portion 12 is higher than in other areas. The piezoelectric element 28 is a piezoelectric element that generates voltage when pressure is applied. The piezoelectric element 28 is, for example, a piezoelectric material. When pressure is applied to a piezoelectric material, strain occurs, and a voltage is generated in accordance with this strain. Therefore, the piezoelectric element 28 generates a voltage due to the stress fluctuation of the annular projection 26 during travel. 【0019】 Inorganic piezoelectric materials and organic piezoelectric materials are selected and used as piezoelectric elements depending on the placement location and other factors. Inorganic piezoelectric materials, which mainly consist of ceramics, have poor flexibility but high power generation efficiency. Organic piezoelectric materials have excellent flexibility but low power generation efficiency. The type of piezoelectric element 28 is selected according to the shape and other conditions of the place where it is placed. Furthermore, the piezoelectric elements 28 placed on the annular projection 26 are the same, and their shape and output are the same. 【0020】 In one example, the piezoelectric elements 28 are intermittently arranged in the annular arrangement surface 29 at positions corresponding to adjacent hub mounting bolt holes 22a, representing high-stress locations. In another example, the piezoelectric elements 28 are arranged in the annular arrangement surface 29 at positions corresponding to hub mounting bolt holes 22a. In yet another example, the piezoelectric elements 28 are arranged in the annular arrangement surface 29 at positions corresponding to adjacent hub mounting bolt holes 22a and at positions corresponding to hub mounting bolt holes 22a. The piezoelectric elements 28 are arranged at equal intervals within the annular arrangement surface 29. The piezoelectric elements 28 may also be arranged in the annular arrangement surface 29 with the same periodicity. The piezoelectric elements 28 may also be provided continuously in the circumferential direction, i.e., without interruption, within the annular arrangement surface 29. 【0021】 This arrangement suppresses the cancellation of outputs between adjacent piezoelectric elements 28. An output voltage with a predetermined period can be obtained from the piezoelectric elements 28. As the output voltage of the piezoelectric elements 28 increases, the output current also increases accordingly, resulting in higher generated power (power generation efficiency). 【0022】 Here, the output voltage was examined for the wheel 10 shown in Figures 1 to 4, when the piezoelectric element 28 was mounted at the position on the inner surface 29 of the annular projection 26 (part A in Figure 2) and when the piezoelectric element 28 was mounted at the position between the decorative holes 27 on the outer side in the vehicle width direction (part B in Figure 1). Figure 5 is a characteristic diagram showing the relationship between elapsed time and voltage when the piezoelectric element 28 is mounted at the position of the annular projection 26 on the inner surface in the vehicle width direction. Figure 6 is a characteristic diagram showing the relationship between elapsed time and voltage when the piezoelectric element 28 is mounted between the decorative holes 27 on the outer surface in the vehicle width direction. In Figures 5 and 6, the vertical and horizontal axis scales are the same. 【0023】<Measurement conditions> ・Wheel / tire: 14×41 / 2 / 155 / 65R14 ・Air pressure: 220kPa ・Test load: 3.7kN ・Test speed: 10km / h From Figures 5 and 6, it can be confirmed that when the piezoelectric element 28 is mounted on the mounting surface 29 on the back side of the annular projection 26 (part A in Figure 2), a higher output voltage can be obtained than when the piezoelectric element 28 is mounted on the position between the decorative holes 27 on the outer side in the vehicle width direction (part B in Figure 1). This is because the stress on the mounting surface 29 is higher than that on the position between the decorative holes 27. 【0024】 The electricity generated by the piezoelectric element 28 is stored in a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride secondary battery. The secondary battery is, for example, an automotive battery and is located on the chassis. In this case, the electricity generated by the piezoelectric element 28 is stored in the secondary battery located on the chassis and used as part of the vehicle's power. Alternatively, the secondary battery may be located on the wheel 10. For example, the wheel 10 may have light-emitting elements such as LEDs for illumination. The wheel 10 may also have detection elements such as sensors for detecting abnormalities in the connection with the hub. These elements, as well as communication elements for exchanging detection data and control data with other communication devices, are powered by the secondary battery located on the wheel 10. 【0025】 <Effects of the First Embodiment> The wheel 10 described above can obtain the following effects: (1-1) The piezoelectric element 28 for power generation is less prone to failure when placed on the wheel 10 than when placed on the tire. 【0026】 (1-2) The annular projection 26 is a location where stress is concentrated more than in other parts of the disk portion 12. Therefore, by placing the piezoelectric element 28 on the annular projection 26, the power generation efficiency of the piezoelectric element 28 can be increased. 【0027】(1-3) By intermittently arranging multiple piezoelectric elements 28 on the annular projection 26, it is possible to suppress the cancellation of the outputs of adjacent piezoelectric elements 28. (1-4) By arranging the piezoelectric elements 28 on the arrangement surface 29, which is the inner surface of the annular projection 26 in the vehicle width direction, the piezoelectric elements 28 can be made less visible from the outside in the vehicle width direction. 【0028】 (1-5) Since the piezoelectric element 28 is positioned on the mounting surface 29 of the annular projection 26, which is part of the disk portion 12, wiring to the secondary battery becomes easier. For example, if the piezoelectric element 28 is positioned on the outer circumferential surface of the rim portion 11, a through hole or the like connected to the inner circumference of the rim portion 11 would be necessary for wiring. In this respect, when the piezoelectric element 28 is positioned on the mounting surface 29 of the annular projection 26, it becomes unnecessary to provide a through hole for wiring in the rim portion 11, whether the secondary battery is positioned in the vehicle or in the inner space of the wheel 10. Therefore, when the piezoelectric element 28 is positioned on the mounting surface 29 of the annular projection 26, wiring to the secondary battery can be easily connected. 【0029】 (1-6) Piezoelectric elements 28 can also be placed on steel wheels, i.e., steel wheels. <Second Embodiment> As shown in Figures 7 and 8, the vehicle wheel 30 according to the second embodiment is a wheel used on trucks, buses, commercial vehicles, etc. The wheel 30 comprises a rim portion 31 and a disc portion 32. The rim portion 31 and the disc portion 32 are made of metal. The rim portion 31 and the disc portion 32 are made of a metal containing at least iron, or a metal containing at least aluminum. The wheel 30 is a wheel roll-formed or press-formed from a steel plate. The disc portion 32 is welded to the annular rim portion 31 to form the wheel 30. 【0030】The rim portion 31 includes an inner flange portion 33, an inner bead seat portion 34, a drop portion 35, an outer bead seat portion 36, and an outer flange portion 37. In Figures 7 and 8, the inner side in the wheel axis direction, i.e., the side closer to the inside of the vehicle, when the wheel 30 is mounted on a vehicle, is indicated as "in," and the outer side in the wheel axis direction is indicated as "out." When the wheel 30 is mounted on a vehicle, the inner flange portion 33 and the inner bead seat portion 34 are located closer to the inside of the vehicle in the wheel axis direction than the outer bead seat portion 36 and the outer flange portion 37. In other words, when the wheel 30 is mounted on a vehicle, the outer bead seat portion 36 and the outer flange portion 37 are located closer to the outside of the vehicle in the wheel axis direction than the inner flange portion 33 and the inner bead seat portion 34. 【0031】 The disc portion 32 includes a hub hole 41, a hub mounting portion 42, a disc intermediate portion 43, and a disc flange portion 44. The hub hole 41 is located in the center of the disc portion 32 in the disc radial direction (wheel radial direction). 【0032】 The hub mounting portion 42 is provided around the hub hole 41. The hub mounting portion 42 is flat and lies in a plane intersecting the disc axis direction (wheel axis direction). Multiple hub mounting bolt holes 42a are provided in the middle of the hub mounting portion 42 in the radial direction of the disc. The hub mounting bolt holes 42a are provided at equal intervals on concentric circles in the circumferential direction of the disc (circumferential direction of the wheel). Hub mounting bolts extending from the hub are inserted through the hub mounting bolt holes 42a. Hub nuts are then screwed onto the hub mounting bolts. In this way, the wheel 30 is fixed to the hub. 【0033】 The disc flange portion 44 is the part that is fitted into and joined to the rim portion 31. The disc flange portion 44 is joined to the outer bead seat portion 36 by welding, riveting, adhesive, etc. The disc flange portion 44 may also be joined to the drop portion 35. 【0034】The intermediate disc portion 43 is provided between the hub mounting portion 42 and the disc flange portion 44 in the radial direction of the disc, and is the portion that connects the hub mounting portion 42 and the disc flange portion 44 in the radial direction of the disc. The intermediate disc portion 43 has a portion that is located outward in the disc axial direction from the hub mounting portion 42 and the disc flange portion 44. At least the top of the intermediate disc portion 43 is located outward in the disc axial direction from the hub mounting portion 42 and the disc flange portion 44. 【0035】 The disc flange portion 44 is the part that is fitted into and joined to the rim portion 31. The disc flange portion 44 is joined to the outer bead seat portion 36 by welding, riveting, adhesive, etc. The disc flange portion 44 may also be joined to the drop portion 35. 【0036】 The intermediate disc portion 43 is provided between the hub mounting portion 42 and the disc flange portion 44 in the radial direction of the disc, and is the portion that connects the hub mounting portion 42 and the disc flange portion 44 in the radial direction of the disc. In the radial direction of the disc, the hub mounting portion 42 side of the intermediate disc portion 43 extends outward in the radial direction of the disc and outward in the axial direction of the disc from the hub mounting portion 42. In the radial direction of the disc, the disc flange portion 44 side of the intermediate disc portion 43 extends outward in the radial direction of the disc and inward in the axial direction of the disc. 【0037】 Decorative holes 45 are formed in the middle portion 43 of the disc. The decorative holes 45 are, for example, circular. The decorative holes 45 are located in the middle portion of the disc in the radial direction of the disc. Multiple decorative holes 45 are provided at equal intervals in the circumferential direction of the disc. The spaces between the decorative holes 45 are connecting regions 46 that function as spokes, connecting the inner and outer regions of the disc's middle portion 43 to the decorative holes 45. 【0038】 <Piezoelectric element> By the way, in the wheel 30, the inner surface in the vehicle width direction is a surface that is difficult to see from the outside. In the connecting region 46, the inner surface in the vehicle width direction is the arrangement surface 48 on which the piezoelectric element 47, which serves as a power generation element, is arranged. The piezoelectric element 47 is positioned in a location within the disc portion 32 where the stress is higher than at other locations. 【0039】Here, Figure 9 shows the stress distribution on the outer surface of the wheel 30 in the vehicle width direction when the vehicle load is applied to the wheel 30 from all sides. Figure 10 shows the stress distribution on the inner surface of the wheel 30 in the vehicle width direction when the vehicle load is applied to the wheel 30 from all sides. Darker colors indicate higher stress. 【0040】 In Figures 9 and 10, it can be seen that the stress in the connecting region 46 within the disk portion 32 is higher than in other regions. More specifically, the location with high stress is adjacent to the decorative holes 45 between two adjacent decorative holes 45, and is closer to the hub mounting portion 42 than to the disk flange portion 44. The piezoelectric element 47 is positioned to straddle the two high-stress locations adjacent to the two decorative holes 45 that constitute the connecting region 46. The piezoelectric element 47 generates a voltage due to stress fluctuations in that region during driving. The piezoelectric element 47 is a piezoelectric element that generates a voltage when pressure is applied. 【0041】 Furthermore, the piezoelectric element 47 is, for example, a piezoelectric body. As the piezoelectric body, inorganic piezoelectric bodies and organic piezoelectric bodies are selected and used depending on the placement location and other factors. Inorganic piezoelectric bodies have poor flexibility because they mainly consist of ceramics, but have high power generation efficiency. Organic piezoelectric bodies have excellent flexibility but low power generation efficiency. The type of piezoelectric element 47 is selected according to the shape and other conditions of the place where it is to be placed. Also, piezoelectric elements 47 placed between two adjacent decorative holes 45, adjacent to the decorative holes 45, and closer to the hub mounting portion 42 than the disc flange portion 44, are the same, and their shape and output are the same. 【0042】The piezoelectric element 47 is disposed at a position adjacent to the decorative hole 45 between two adjacent decorative holes 45 and closer to the hub mounting portion 42 than the disk flange portion 44. The piezoelectric elements 47 are periodically and intermittently arranged in the circumferential direction. By being arranged in this way, it is possible to suppress the adjacent piezoelectric elements 47 from canceling out their outputs. Also, it can be confirmed that the piezoelectric element 47 can obtain an output voltage with a predetermined period. When the output voltage of the piezoelectric element 47 increases, the output current also increases accordingly, so that the power generation power (power generation efficiency) also increases. 【0043】 The power generated by the piezoelectric element 47 is stored in a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride secondary battery. The secondary battery is, for example, for vehicle-mounted use and is disposed on the chassis. In this case, the power generated by the piezoelectric element 47 is stored in the secondary battery disposed on the chassis and used as part of the power of the vehicle. Also, the secondary battery may be disposed on the wheel 30. For example, there is a wheel 30 on which a light-emitting element such as an LED is disposed for decorative lighting. Also, a detection element such as a sensor for detecting an abnormal fastening to the hub may be disposed on the wheel 30. Power is supplied from the secondary battery disposed on the wheel 30 to these elements and to a communication element or the like for communicating detection data and control data with other communication devices. The power generated by the piezoelectric element 47 is stored in the secondary battery disposed on the wheel 30. 【0044】 <Effect of the Second Embodiment> The wheel 30 as described above can obtain the following effects. (2-1) By disposing the piezoelectric element 47 for power generation on the wheel 30, it becomes less likely to fail than when disposed on a tire. 【0045】 (2-2) On the arrangement surface 48 of the connection region 46, the position adjacent to the decorative hole 45 between two adjacent decorative holes 45 and closer to the hub mounting portion 42 than the disk flange portion 44 is a position where stress concentrates more than other portions in the disk portion 32. Therefore, by disposing the piezoelectric element 47 in this region, the power generation efficiency of the piezoelectric element 47 can be increased. 【0046】(2-3) The piezoelectric elements 47 are positioned between two adjacent decorative holes 45, adjacent to the decorative holes 45, and closer to the hub mounting portion 42 than to the disc flange portion 44, so that they are intermittently arranged in the circumferential direction. Therefore, it is possible to suppress the cancellation of the outputs of adjacent piezoelectric elements 47. 【0047】 (2-4) By arranging the piezoelectric element 47 on the arrangement surface 48, which is the inner surface in the vehicle width direction of the connecting region 46, it can be made less visible from the outside in the vehicle width direction. (2-5) The piezoelectric element 47 is arranged on the arrangement surface 48 of the connecting region 46, which is part of the disc portion 32, at a position adjacent to the decorative holes 45 between two adjacent decorative holes 45, and at a position closer to the hub mounting portion 42 than to the disc flange portion 44. Therefore, wiring to the secondary battery becomes easier. For example, if the piezoelectric element 47 is arranged on the outer circumference of the rim portion 31, a through hole or the like connected to the inner circumference of the rim portion 31 will be necessary for wiring. In this respect, if the piezoelectric element 47 is arranged on the arrangement surface 48 of the connecting region 46, it will not be necessary to provide a through hole for wiring in the rim portion 31, whether the secondary battery is installed in the vehicle or in the inner space of the wheel 30, etc. Therefore, if the piezoelectric element 47 is arranged on the arrangement surface 48 of the connecting region 46, wiring to the secondary battery can be made easier. 【0048】 (2-6) The piezoelectric element 47 can also be placed on a steel wheel. <Modification of the second embodiment> In the second embodiment described above, the piezoelectric element 47 is placed on the placement surface 48, which is the inner surface (first surface) in the vehicle width direction. In contrast, in Figure 11, which is a modification of the second embodiment, the piezoelectric element 47 is placed on the outer surface (second surface) in the vehicle width direction. In the case of commercial vehicles, the rear wheels may be double tires. In such cases, the surface on which the piezoelectric element 47 is placed may be the outer surface (second surface) or the inner surface (first surface), depending on whether the wheel 30 is placed on the inside or outside. For example, in a double tire, the piezoelectric element 47 is placed on the inner surface (first surface) of the inner wheel 30 as shown in Figure 8, and the piezoelectric element 47 is placed on the outer surface (second surface) of the outer wheel 30 as shown in Figure 11. 【0049】 Incidentally, when assuming a double tire, the outer surface and the inner surface of the inner wheel 30 and the outer wheel 30 arranged outside do not show the same surface. Therefore, here, based on the inner wheel 30 located inside, the inner surface in the vehicle width direction is also referred to as the first surface, and the outer surface is also referred to as the second surface. 【0050】 As shown in FIG. 9, also on the outer surface (second surface), the position where the piezoelectric element 47 is arranged is a position adjacent to the decorative hole 45 between two adjacent decorative holes 45 in the connection region 46, and is closer to the hub mounting portion 42 than the disk flange portion 44. Therefore, on the outer surface (second surface), the piezoelectric element 47 is arranged so as to straddle two positions with high stress adjacent to the two decorative holes 45 constituting the connection region 46. In such a case, the piezoelectric element 47 may be made inconspicuous and protected by covering the piezoelectric element 47 with a component. 【0051】 Here, in the wheel 30 shown in FIGS. 7 to 11, when the piezoelectric element 47 is arranged at a portion (portion A in FIG. 11) straddling two positions with high stress adjacent to the two decorative holes 45 on the outer surface (second surface), and when the piezoelectric element 47 is arranged at a position along the outer periphery of the hub mounting portion 42 on the inner surface (first surface) (portion B in FIG. 8), the output voltages were confirmed. Incidentally, in FIG. 8, the position of portion B is inside of the position of portion A in FIG. 11, closer to the hub mounting portion 42, and does not overlap with the position of portion A. 【0052】 FIG. 12 is a characteristic diagram showing the relationship between the elapsed time and the voltage when the piezoelectric element 47 is arranged at a position (portion A in FIG. 11) between two decorative holes 45 and closer to the hub mounting portion 42 than the disk flange portion 44 on the outer surface (second surface). FIG. 13 is a characteristic diagram showing the relationship between the elapsed time and the voltage when the piezoelectric element 47 is arranged at a position along the outer periphery of the hub mounting portion 42 (portion B in FIG. 8) on the inner surface (first surface). In FIGS. 12 and 13, the scales on the vertical axis are the same. 【0053】<Measurement conditions> ・Wheel / tire: 22.5 x 7.50 / 275 / 80R22.5 ・Air pressure: 900 kPa ・Test load: 16.9 kN ・Test speed: 15 km / h From Figures 12 and 13, it can be confirmed that when the piezoelectric element 47 is attached to the part where the stress is high adjacent to the two decorative holes 45 that constitute the connecting region 46 (part A in Figure 11), a higher output voltage can be obtained than when the piezoelectric element 47 is attached to a position along the outer circumference of the hub mounting part 42 (part B in Figure 8). 【0054】 Furthermore, the first and second embodiments can be further modified as appropriate as follows: In the first and second embodiments, the metal of the wheels 10 and 30 may be aluminum. Alternatively, it may be a titanium alloy, magnesium alloy, or the like. 【0055】 In the first embodiment, the piezoelectric element 28 may be positioned on the outer surface of the annular projection 26 in the vehicle width direction. In this case, the piezoelectric element 28 can be made less conspicuous and protected by covering it with an accessory. 【0056】 In the first embodiment, the piezoelectric element 28 may be placed only on the arrangement surface 29, which is the inner surface in the vehicle width direction of the annular projection 26, or only on the outer surface in the vehicle width direction. Furthermore, it may be placed on both the arrangement surface 29, which is the inner surface in the vehicle width direction, and the outer surface in the vehicle width direction. Furthermore, the piezoelectric element 28 may be placed on the outer or inner surface of the rim portion 11. When the piezoelectric element 28 is placed on the rim portion 11, it is preferable to place it on the drop portion 15. 【0057】- In the first embodiment, the annular projection 26 may be discontinuous in the circumferential direction. The annular projection 26 may be provided at equal intervals with a predetermined gap between them in the circumferential direction. - In the second embodiment, whether the tire is a single tire or a double tire, the piezoelectric element 47 may be positioned adjacent to the decorative holes 45 between two adjacent decorative holes 45 in the connecting region 46, and closer to the hub mounting portion 42 than the disc flange portion 44, and positioned on both the inner surface in the vehicle width direction and the outer surface in the vehicle width direction. Furthermore, if additional piezoelectric elements are to be placed on the rim portion 31, it is preferable to place them on the drop portion 35 or the like. 【0058】 - In addition to the positions in the first and second embodiments, the piezoelectric element may be placed in the disc portion at any other position where the stress during driving is higher than at other positions. - In the case of an aluminum wheel, i.e., a wheel made of aluminum, it may be composed of two parts: a rim portion and a disc portion equipped with a hub mounting portion and spokes. In this case, the rim portion and the disc portion are joined by bolts and nuts, welding, etc. Furthermore, the rim portion may be divided in the axle direction and composed of three parts. 【0059】 Furthermore, the aluminum wheel may be a cast wheel, a forged wheel formed by press drawing from a steel sheet, or a forged aluminum wheel formed from a bullet or casting. As an infinitely rotating body, the wheel 10 of the first embodiment may be a wheel used in commercial vehicles, etc. Also, the wheel 30 of the second embodiment may be a wheel used in passenger cars, etc. In addition, as an infinitely rotating body, it can also be applied to the wheels of work vehicles, bicycle wheels, and railway wheels.

Claims

1. An infinitely rotating body comprising a rim portion and a disc portion disposed inside the ring of the rim portion, wherein a piezoelectric element is disposed in the disc portion at a position where the stress during travel is higher than at other positions.

2. The infinitely rotating body according to claim 1, wherein the disc portion comprises a hub mounting portion, a disc flange portion, a plurality of holes periodically arranged in the circumferential direction between the hub mounting portion and the disc flange portion, and an annular projection that is continuous or discontinuous in the circumferential direction between the hub mounting portion and the holes, and the position where the piezoelectric element is located is the annular projection.

3. The infinitely rotating body according to claim 1, wherein the disc portion comprises a hub mounting portion, a disc flange portion, and a plurality of holes periodically arranged in the circumferential direction between the hub mounting portion and the disc flange portion, and the position where the piezoelectric element is located is between the plurality of holes in the circumferential direction and between the disc flange portion and the hub mounting portion in the radial direction.

4. The infinitely rotating body according to claim 2 or 3, wherein the piezoelectric elements are intermittently arranged in the circumferential direction with the same period.

5. The infinitely rotating body according to claim 2 or 3, wherein the piezoelectric element is arranged on the inner surface of the disc portion in the vehicle width direction.

6. The infinitely rotating body according to claim 2 or 3, wherein the piezoelectric element is arranged on the outer surface of the disc portion in the vehicle width direction.

7. The infinitely rotating body according to claim 1, which is a steel wheel.

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