Airless tire structure

Abstract

To enable a coating film with a uniform thickness to be formed on an inclined surface.SOLUTION: An airless tire structure comprises an inner peripheral ring 4 arranged at a center of an airless tire 1, an outer peripheral ring 5 having a tread layer 7 at an outermost periphery, and a spoke part 6 provided between the inner peripheral ring 4 and the outer peripheral ring 5. The spoke part 6 is provided with connection parts 9a connecting adjacent spokes 8 to each other, in a circumferential direction. The outer peripheral ring 5 has a shearing layer 10 connecting an inner peripheral surface of the tread layer 7. The shearing layer 10 has at least an outer reinforcement layer contacting the inner peripheral surface of the tread layer 7 and an elastomer layer arranged inside the outer reinforcement layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an airless tire structure. [Background technology]

[0002] The airless tire structure disclosed in Patent Document 1 below includes an inner ring, an outer ring, and a spoke portion. The inner ring is disposed at the center of the airless tire and is attached to the vehicle hub via a wheel or directly to the vehicle hub. The outer ring has a tread layer on its outer surface. The spoke portion has a plurality of spokes arranged radially between the inner and outer rings, connecting the outer periphery of the inner ring to the inner periphery of the outer ring. The outer ring further includes, radially inside the tread layer, an outer reinforcing layer, an elastomer layer, and an inner reinforcing layer, in that order from the outer diameter. In Patent Document 1, the elastomer layer is also referred to as an elastomer shear layer or simply a shear layer. The invention disclosed in Patent Document 1 relates to a technology for optimizing the contact pressure distribution between the tire and the road surface by setting an appropriate ratio between the shear modulus and tensile modulus of the outer ring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4852767 Summary of the Invention [Problem to be solved by the invention]

[0004] In the airless tire structure disclosed in Patent Document 1, an elastomer layer with low shear rigidity is sandwiched between an outer reinforcing layer and an inner reinforcing layer with high material elastic modulus. With this structure, the tire load causes shear deformation of the outer ring at the circumferential contact edge, ensuring a sufficient contact length and contact area between the tire and the road surface. It explains that by appropriately setting the shear modulus of elasticity of the elastomer layer relative to the tensile modulus of elasticity of the reinforcing layer, it is possible to obtain a contact area equivalent to that of a pneumatic tire.

[0005] It is well known that tire rolling resistance has a significant impact on a vehicle's fuel economy or electricity consumption. Similar to pneumatic tires, the rolling resistance of airless tires is thought to be primarily due to strain energy loss caused by deformation of the tire structure during rolling. Furthermore, because airless tires support the load with the reaction force generated by deformation of their structure, strain energy loss also occurs in the deformed structure. For this reason, airless tires are generally considered to be at a disadvantage in terms of rolling resistance compared to pneumatic tires.

[0006] The above-mentioned elastomer layer ensures the contact length and contact area by deforming in the shear direction, and therefore, structurally, tends to have a large strain energy loss in the shear direction. In order to ensure the same contact length and contact area as pneumatic tires, it is effective to reduce the elastic modulus of the elastomer layer. However, reducing the elastic modulus of the elastomer layer further increases the strain energy loss generated in the elastomer layer. Furthermore, since elastomer layers generally undergo large deformation in the shear direction, it is often assumed that they will be formed from rubber or other materials to ensure durability. However, rubber generally has a higher loss tangent than materials such as resin, and therefore the strain energy loss generated in the elastomer layer can become a major cause of energy loss in the entire tire.

[0007] In response to the above-mentioned issues, the inventors studied the structural aspects of airless tires to achieve both sufficient contact length and contact area and reduced rolling resistance. As a result, the inventors concluded that an airless tire with a relatively small loss tangent would be effective in achieving both of these goals if the spoke stiffness of the spokes was sufficiently lower than that of the outer ring and capable of large shear deformation similar to the elastomer layer. However, if the stiffness of the spokes were excessively low, the spokes would undergo large deformation accompanied by buckling, which could pose a durability issue for the spokes themselves. Furthermore, if the spokes buckle, the outer ring acts as the main spring to support the load, which could result in high compressive stress, particularly in the outer reinforcing layer, causing the reinforcing layer to buckle.

[0008] The object of the present invention is to provide an airless tire structure that solves the above-mentioned problems by optimizing the structure and shape of the spoke portion and then designing the structure of the outer ring, thereby ensuring a sufficient contact area without increasing the energy loss generated throughout the tire. [Means for solving the problem]

[0009] An airless tire structure according to an embodiment of the present invention includes an inner ring disposed at the center of the airless tire, an outer ring having a tread layer at its outermost periphery, and a spoke structure disposed between the inner ring and the outer ring. The spoke structure includes connecting portions that connect adjacent spokes in the circumferential direction. The outer ring also includes a shear layer in contact with the inner surface of the tread layer. The shear layer includes at least an outer reinforcing layer in contact with the inner surface of the tread layer and an elastomer layer disposed inside the outer reinforcing layer. [Effects of the Invention]

[0010] According to the above aspect of the present invention, it is possible to ensure a sufficient contact area without increasing the energy loss that occurs in the entire tire. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a front view of an airless tire structure according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the outer ring according to the first embodiment of the airless tire structure. [Figure 3] FIG. 3 is a cross-sectional view of the outer ring according to the second embodiment. [Figure 4] FIG. 4 is a cross-sectional view of an outer ring according to a third embodiment. [Figure 5] FIG. 5 is a partial front view showing the deformation state of the airless tire. [Figure 6] FIG. 6 is a cross-sectional view of an outer ring according to the fourth embodiment. [Figure 7] FIG. 7 is a cross-sectional view of an outer ring according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] An airless tire structure according to an embodiment will be described with reference to the drawings.

[0013] FIG. 1 shows a front view of an airless tire (non-pneumatic tire) 1 having a structure according to this embodiment. The annular airless tire 1 of this embodiment is attached to a wheel 2 made of a highly rigid part such as metal. Bolt holes 3 are formed in the wheel 2, and the wheel 2 is fixed to the vehicle hub by hub bolts inserted into the bolt holes 3. The airless tire 1 includes an inner ring 4, an outer ring 5, and spokes 6.

[0014] The inner ring 4 is disposed in the center of the airless tire 1 and is attached to the outer periphery of the wheel 2. The outer ring 5 has a tread layer 7 on its outermost periphery. The spoke portion 6 has a plurality of spokes 8 arranged radially between the inner ring 4 and the outer ring 5, connecting the outer periphery of the inner ring 4 and the inner periphery of the outer ring 5. The airless tire 1 comes into contact with the road surface at the tread layer 7 of the outer ring 5.

[0015] The multiple spokes 8 of the spoke portion 6 are arranged approximately evenly in the circumferential direction. Each of the spokes 8 has a zigzag shape when viewed from the direction of the rotation axis of the airless tire 1. The spoke portion 6 is provided with connecting portions 9a that connect adjacent spokes 8 in the circumferential direction. The connecting portions 9a are connected around the entire circumference to form an intermediate ring 9. The multiple intermediate rings 9 are arranged concentrically with respect to the center O of the airless tire 1. Each intermediate ring 9 is connected to the spoke 8 at a bent portion of the zigzag shape of the spoke 8. The connecting portions 9a, i.e., the intermediate ring 9, transmit the ground contact load between adjacent spokes 8, and the load can be supported even when combined with an outer ring 5 with low rigidity.

[0016] The spoke portion 6, i.e., the spokes 8 and the intermediate ring 9, are formed from an elastic material. In this embodiment, the spokes 8 and the intermediate ring 9 are integrally formed from the same material, but they may be made from different materials as long as they are connected to each other. The spokes 8 and the intermediate ring 9 are primarily made from rubber or resin, and various existing materials such as thermoplastic resin and thermosetting resin can be used. The spokes 8 in this embodiment have the same width as the airless tire, but may be divided in the direction of the rotation axis. If the spokes 8 are divided in the direction of the rotation axis, the circumferential arrangement pitch of the front spokes 8 and the rear spokes 8 may be offset. Furthermore, the bending directions of the front spokes 8 and the rear spokes 8 may be opposite to each other.

[0017] A cross-sectional view of the outer ring 5, i.e., a cross-sectional view taken along line II-II in FIG. 1, is shown in FIG. 2. The outer ring 5 has the above-mentioned tread layer 7 and a shear layer 10 disposed radially inward of the tread layer 7. The shear layer 10 contacts the inner circumferential surface of the tread layer 7. The shear layer 10 has at least an outer reinforcing layer 11 and an elastomer layer 12. The outer reinforcing layer 11 contacts the inner circumferential surface of the tread layer 7, and the elastomer layer 12 is disposed inside the outer reinforcing layer 11. FIG. 2 shows the outer ring 5 (first embodiment) having this shear layer 10 with a minimum configuration.

[0018] From the viewpoints of durability and adhesiveness to other parts, the outer reinforcing layer 11 preferably has a composite structure in which reinforcing fibers such as steel cords are embedded in rubber, but the form is not limited thereto. The outer reinforcing layer 11 may also be made of a resin such as a hard thermoplastic resin or a metal such as a thin metal film. The elastomer layer 12 is formed from a rubber or resin material. The composite structure of the outer reinforcing layer will be described later in the third embodiment.

[0019] The tread layer 7 ensures a coefficient of friction with the road surface and has various properties such as wear resistance. The tread layer 7 has properties equivalent to those of the tread layer of a conventional pneumatic tire. When the airless tire 1 having the above-described configuration is mounted on a vehicle, it supports the vehicle, transmits braking and driving forces to the road surface, and generates force in the lateral direction of the vehicle due to deformation of the airless tire 1.

[0020] FIG. 3 shows a second embodiment of the outer ring 5. The shear layer 10 of the second embodiment further includes an inner reinforcing layer 13 on the opposite side of the elastomer layer 12 from the outer reinforcing layer 11. The inner reinforcing layer 13 is in contact with the inner circumferential surface of the elastomer layer 12. Although not shown in FIG. 3, the radially outer ends of the spokes 8 are connected to the inner reinforcing layer 13. The material of the inner reinforcing layer 13 can be the same as that of the outer reinforcing layer 11, but the Young's modulus of the inner reinforcing layer 13 is lower than that of the outer reinforcing layer 11.

[0021] FIG. 4 shows a third embodiment of the outer ring 5. The shear layer 10 of this embodiment has a spoke connection layer 14 radially inward of the elastomer layer 12. As in the above-described embodiments, the tread layer 7 is disposed radially outward of the shear layer 10. The spoke connection layer 14 functions as an intermediate material to ensure bonding when bonding between the spoke portion 6 and the elastomer layer 12 is difficult. An inner reinforcing layer 13 may be provided radially inward of the spoke connection layer 14 (see the fourth and fifth embodiments described below). Unlike the above-described embodiments, the outer reinforcing layer 11 of this embodiment has a composite structure.

[0022] Specifically, the outer reinforcing layer 11 forms a composite structure containing reinforcing fibers 15, which are steel cords. The reinforcing fibers 15 are arranged so as to intersect in the circumferential direction of the airless tire 1. In this embodiment, four reinforcing fibers 15 are contained in the outer reinforcing layer 11, and the angles of the reinforcing fibers 15 adjacent in the radial direction are paired. More specifically, when the crossing angle of the reinforcing fiber 15 with respect to the circumferential direction of the airless tire 1 is +α°, the crossing angle of the adjacent reinforcing fibers 15 with respect to the circumferential direction is +-α°. The number of reinforcing fibers 15 is not limited to that of this embodiment.

[0023] The strain energy loss generated in the outer ring 5 when the airless tire 1 of this embodiment is restrained at its center O (using the wheel 2) and subjected to a ground load was compared with that of a conventional airless tire. In conventional airless tires, the elastomer layer sandwiched between the reinforcing layers is primarily deformed by shear around the circumferential contact edge, thereby ensuring the tire-road contact length and contact area. For this reason, high strain energy loss occurs in the elastomer layer 12 around the circumferential contact edge, where the amount of deformation is large, which can be a factor in worsening rolling resistance.

[0024] On the other hand, in the airless tire 1 of this embodiment, the rigidity of the outer ring 5 decreases, increasing the deformation of the spoke portion 6. As a result, strain energy loss in the elastomer layer 12 at the circumferential contact edge is mitigated, and the strain energy loss is distributed throughout the entire airless tire 1, from the outer ring 5 to the spoke portion 6. Ensuring strain energy in the spoke portion 6, which has a relatively small material loss tangent, makes it possible to reduce overall energy loss. It has been confirmed that even with the structure of this embodiment, the outer ring 5 undergoes shear deformation, ensuring the contact length and contact area.

[0025] The airless tire 1 of this embodiment is provided with a connecting portion 9a (intermediate ring 9) in the spoke portion 6 that transmits a ground contact load between adjacent spokes 8 when combined with the outer peripheral ring 5. FIG. 5 shows the deformation of the outer peripheral ring 5 and the spoke portion 6 when a ground contact load is applied to the airless tire 1. As shown in FIG. 5, when the spoke portion 6 is combined with an outer peripheral ring 5 with low rigidity, the spoke portion 6 is significantly deformed by the ground contact load, but at the same time, the intermediate ring 9 is also significantly deformed, so that the ground contact load is transmitted between adjacent spokes 8. As a result, local buckling of the spokes 8 near the ground contact area is suppressed, and the airless tire 1 as a whole can support the load.

[0026] Furthermore, the spokes 6 can be considered to be a configuration of diamond-shaped cells arranged side by side, and this diamond-shaped cell shape is characterized by a lower modulus of elasticity in the shear direction relative to the modulus of elasticity in the tensile direction. Focusing on the cell shape under a ground load, it can be seen that a shear deformation mode occurs in the spokes 6 due to the bending stress generated in the spokes 6. This deformation mode causes the entire spokes 6 to deform in a mode similar to that of the elastomer layer 12, making this configuration of the spokes 6 effective in ensuring contact length and contact area. By combining the characteristics of the spokes 6 with the structure of the outer ring 5 described above, which disperses strain energy, it is possible to more reliably achieve both reduced rolling resistance and ensuring contact length and contact area, which was difficult with conventional technology.

[0027] In order to achieve the above-described functions, it is necessary to appropriately set the rigidity and modulus of elasticity of each portion (member). First, the radial (longitudinal) rigidity of the entire airless tire 1 can be treated as the sum of the rigidity of the outer ring 5 and the rigidity of the spoke portion 6. In order to obtain the effects of this embodiment, the radial rigidity of the outer ring 5 alone is preferably 1 / 10 or less, and more preferably 1 / 15 or less, of the radial rigidity of the entire airless tire 1.

[0028] To fulfill the above-described functions of the outer ring 5, it is desirable that the Young's modulus (elastic modulus) of the elastomer layer 12 be 5 to 70 MPa and the thickness be 5 to 15 mm, and it is more desirable that the Young's modulus be 20 to 40 MPa and the thickness be 6 to 10 mm. If the Young's modulus of the elastomer layer 12 is excessively high (generally, this can also be said to be excessively high rigidity) or if the thickness is large, the radial rigidity of the outer ring 5 will deviate from the above range. On the other hand, if the Young's modulus is excessively low (generally, this can also be said to be excessively low rigidity) or if the thickness is small, it will be difficult for the airless tire 1 to support the load.

[0029] The Young's modulus of the reinforcing fibers 15 is desirably 70 to 200 GPa, which is a typical value for a steel cord. In particular, strong compressive stress occurs in the reinforcing fibers 15 closest to the tread layer 7 when a ground contact load is applied, so if the Young's modulus of these reinforcing fibers 15 is low, there is a risk of buckling of the outer reinforcing layer 11. There are no particular restrictions on the Young's modulus of the material of the reinforcing fibers 15 that make up the outer reinforcing layer 11, and it is sufficient that an appropriate rubber or resin is used as this material depending on the properties of the reinforcing fibers 15.

[0030] In order for the spoke portion 6 to support a load without buckling, the Young's modulus of the spoke portion 6 including the intermediate ring 9 is preferably 10 to 100 MPa, and more preferably 30 to 80 MPa. If the Young's modulus of the spokes 8 and the intermediate ring 9 is low, the spokes 8 will buckle and will not be able to support the ground contact load. If the Young's modulus of the spoke portion 6 is within the above range, an airless tire 1 that meets the desired rigidity for a typical passenger car can be designed by appropriately changing the number and thickness of the spokes 8 and the intermediate ring 9.

[0031] The angle between the intermediate ring 9 and the spokes 8 is preferably within a range of 50 to 75 degrees with respect to a direction parallel to the intermediate ring 9, and preferably decreases radially outward. If this angle is less than 50 degrees, the radial rigidity of the airless tire 1 decreases, making it difficult to support the load. On the other hand, if this angle exceeds 75 degrees, the diamond-shaped cell shape of the spoke portion 6 does not exhibit the characteristic of shear deformation under load, making it difficult to ensure the contact length and contact area. Furthermore, if this angle decreases radially outward, the radial rigidity of the spoke portion 6 at the radially outer side decreases, facilitating load transmission between adjacent spokes 8. Furthermore, if this angle decreases radially outward, the diamond-shaped cell shape at the radially outer side is more susceptible to shear deformation, which is advantageous in terms of ensuring the contact length and contact area.

[0032] Figure 6 shows a fourth embodiment of the outer ring 5. The shear layer 10 of this embodiment is different from the shear layer 10 of the third embodiment in that an inner reinforcing layer 13 is added between the elastomer layer 12 and the spoke connection layer 14. The outer reinforcing layer 11 also contains two reinforcing fibers 15. The inner reinforcing layer 13, like the outer reinforcing layer 11, has a composite structure containing two reinforcing fibers 15.

[0033] If the outer ring 5 having the shear layer 10 does not have an inner reinforcing layer 13 at the boundary with the spoke portion 6, the shear stress generated at the interlayer interface between the spoke portion 6 and the outer ring 5 tends to be higher than in the prior art. For this reason, as in the second embodiment, an inner reinforcing layer 13 having a Young's modulus lower than that of the outer reinforcing layer 11 is added. If the Young's modulus of the inner reinforcing layer 13 is higher than that of the outer reinforcing layer 11, the strain energy of the elastomer layer 12 increases, as in the prior art, and the desired effect described above cannot be obtained. The reinforcing fibers 15 contained in the inner reinforcing layer 13 are organic fibers with a relatively low Young's modulus, and it is desirable that the Young's modulus be 20 GPa or less.

[0034] 7 shows a fifth embodiment of the outer ring 5. The shear layer 10 of this embodiment differs from the shear layer 10 of the fourth embodiment in that an intermediate reinforcing layer 16 is added inside the elastomer layer 12 between the outer reinforcing layer 11 and the inner reinforcing layer 13. The intermediate reinforcing layer 16 also has a composite structure containing reinforcing fibers 15, similar to the outer reinforcing layer 11 and the inner reinforcing layer 13.

[0035] The shear layer 10 of the second embodiment described above is configured such that the difference in Young's modulus between the outer reinforcement layer 11 and the inner reinforcement layer 13 is large. However, if the difference in Young's modulus between the outer reinforcement layer 11 and the inner reinforcement layer 13 is large, shear strain occurring between the elastomer layer 12 and the reinforcement layer 11 or 13 may cause the reinforcement layer 11 or 13 to peel off. This problem can be resolved by providing the shear layer 10 with multiple reinforcement layers 11, 13, and 16 whose stiffness (Young's modulus) gradually decreases from the radially outer side to the radially inner side. Similar to the reinforcement fibers 15 of the outer reinforcement layer 11, the two reinforcement fibers 15 contained in the intermediate reinforcement layer 16 are also contained in such a way that the angles of adjacent reinforcement fibers 15 in the radial direction are paired. The number of reinforcement fibers 15 is not limited to that of this embodiment. Two or more intermediate reinforcement layers 16 may be provided.

[0036] The outer ring 5 is required to transmit loads in the circumferential direction and to shear-deform to ensure the contact length and contact area. When multiple intermediate reinforcing layers 16 are provided, the shear layer 10 including the elastomer layer 12 and reinforcing layers 11, 13, and 16, and the outer ring 5 equipped with the tread layer 7 can be regarded as a single beam, and its tensile stiffness and shear stiffness can be specified. The tensile stiffness can be adjusted by the angle of the reinforcing fibers 15, the Young's modulus of the reinforcing layers 11, 13, and 16, and the volume ratio of the reinforcing fibers 15 to the elastomer layer 12. The shear stiffness can be adjusted by the Young's modulus and thickness of the elastomer layer 12. When the outer ring 5 is regarded as a single beam, the ratio of the shear stiffness to the tensile stiffness of the beam (shear stiffness:tensile stiffness) is preferably within the range of 1:700 to 1:50.

[0037] The advantages of the airless tire structure according to the above embodiment will be described below.

[0038] As mentioned above, Patent Document 1 proposes an airless tire with an outer ring in which an elastomer layer with low shear rigidity is sandwiched between a pair of reinforcing layers with high material elasticity. While this configuration is effective in ensuring contact patch length and contact patch area, when a ground load is applied, strain energy loss throughout the tire, i.e., rolling resistance, can increase, mainly due to shear strain in the elastomer layer sandwiched between the hard reinforcing layers.

[0039] The airless tire structure according to the above embodiment includes an inner ring 4 disposed at the center of the airless tire 1, an outer ring 5 having a tread layer 7 at its outermost periphery, and a spoke portion 6 provided between the inner ring 4 and the outer ring 5. The spoke portion 6 is provided with connecting portions 9a that connect adjacent spokes 8 in the circumferential direction. The outer ring 5 also has a shear layer 10 that contacts the inner surface of the tread layer 7. The shear layer 10 has at least an outer reinforcing layer 11 that contacts the inner surface of the tread layer 7, and an elastomer layer 12 disposed inside the outer reinforcing layer 11.

[0040] As described above, the shear layer 10 of the outer ring 5 is composed of, from the outside of the tire, the outer reinforcing layer 11 and the elastomer layer 12. With this configuration, compared to the conventional technology of Patent Document 1, the rigidity of the outer ring 5 is lower relative to the spoke portion 6, which increases the amount of deformation of the spokes 8 and transfers strain energy loss from the elastomer layer 12 to the spoke portion 6. As a result, strain energy loss in the elastomer layer 12 decreases and strain energy loss in the spoke portion 6 increases. Note that with this configuration, the radial rigidity of the airless tire 1 also decreases, but by optimizing the shape and material elastic modulus of the spoke portion 6, it is possible to achieve radial rigidity equivalent to that of the conventional technology.

[0041] The energy loss throughout the entire airless tire 1 can be expressed simply as the product of the loss tangent of each component and the strain energy loss. Generally, the loss tangent of the material used in the spoke portion 6 is smaller than that of the material used in the elastomer layer 12. Therefore, by adopting the above-described configuration of the shear layer 10 and ensuring strain energy in the spoke portion 6, which has a relatively small loss tangent, the energy loss throughout the airless tire 1 can be reduced.

[0042] The inner reinforcing layer in the prior art of Patent Document 1 not only excites shear deformation of the outer ring, but also plays a role in transmitting stress due to ground contact load in the circumferential direction of the airless tire. By transmitting the load in the circumferential direction using the reinforcing layer, the airless tire transmits stress in the spoke portion 6 near the contact point caused by the ground contact load in the circumferential direction, and supports the vehicle load with the reaction force generated when the entire structure of the airless tire is deformed.

[0043] In the above embodiment, the spoke portion 6 is provided with connecting portions 9a that connect adjacent spokes 8 in the circumferential direction, and stress is transmitted circumferentially between adjacent spokes 8 via the connecting portions 9a. By transmitting stress circumferentially through the spoke portion 6 provided with the connecting portions 9a, the entire structure of the airless tire 1 can support a ground contact load, even if the outer ring 5 has only the outer reinforcing layer 11 (see Example 1). The spoke portion of the airless tire of the prior art disclosed in Patent Document 1 does not have a configuration like the connecting portions 9a of the above embodiment that transmits a ground contact load between adjacent spokes. Therefore, if the configuration of the shear layer 10 of the above embodiment were adopted in the airless tire of the prior art disclosed in Patent Document 1, local buckling due to the ground contact load would occur near the contact point, making it impossible to support the load.

[0044] In the prior art of Patent Document 1, a pair of reinforcing layers with high elastic modulus sandwich an elastomer layer with low shear rigidity, allowing the outer ring to shear deform and ensure a sufficient contact length and area. In contrast, the above embodiment employs a structure in which an elastomer layer 12 is sandwiched between an outer reinforcing layer 11 and spokes 6. Because the spokes 6 have a lower elastic modulus than the reinforcing layers, the amount of shear deformation of the elastomer layer 12 tends to decrease, resulting in a slight decrease in the contact length and area. However, by appropriately setting the rigidity of each component, it is possible to maintain a contact area substantially equivalent to that of the prior art. As in the above embodiment, a structure combining an outer ring 5 having a shear layer 10 with spokes 6 having connecting portions 9a as described above makes it possible to simultaneously ensure a sufficient contact length and area and reduce rolling resistance, which was difficult with conventional airless tires.

[0045] Furthermore, in the airless tire structure according to the above embodiment, the connecting portions 9a form multiple intermediate rings 9 concentric with the center of the airless tire 1. This structure allows for efficient circumferential stress transmission. Various shapes, such as a honeycomb structure, are conceivable as a structure for transmitting ground contact loads between adjacent spokes 8. While a honeycomb structure also provides connecting portions between adjacent spokes, the rigidity of each cell in the honeycomb structure is high, allowing cells near the contact point to withstand high stress without buckling when a load is applied to the airless tire. However, on the other hand, a honeycomb structure is less able to transmit stress in the circumferential direction than an intermediate ring 9. In the above embodiment, which includes multiple intermediate rings 9, the spoke portion 6, including the spokes 8 and the intermediate rings 9, deforms significantly near the contact point. However, due to the deformation of the intermediate rings 9, the deformation of the spoke portion 6 near the contact point is transmitted in the circumferential direction via the concentric intermediate rings 9, resulting in efficient circumferential transmission of stress due to the ground contact load.

[0046] By combining the spoke portion 6 having a concentric intermediate ring 9 with the outer ring 5 having the shear layer 10 with the outer reinforcing layer 11 and the elastomer layer 12, and the tread layer 7, the load is transmitted in the circumferential direction by the intermediate ring 9, instead of the inner reinforcing layer disclosed in Patent Document 1. Therefore, even if the only reinforcing layer is the outer reinforcing layer 11 (see Example 1), the entire structure of the airless tire 1 can support the ground contact load. Compared to when a metal is used as the inner reinforcing layer, which is a typical example in the prior art, the vertical rigidity tends to be lower due to the difference in the elastic modulus of the material, but by optimizing the rigidity of the spoke portion 6 and the elastomer layer 12, it is possible to obtain the same vertical rigidity.

[0047] Furthermore, according to the airless tire structure of the above embodiment, each of the spokes 8 has a zigzag shape when viewed from the rotational axis direction of the airless tire 1, and the intermediate ring 9 is connected to the spokes 8 at a bent portion of this zigzag shape. The spokes can have various shapes, such as a straight shape in the radial direction or an arc shape, but in the above embodiment, they are zigzag. The zigzag-shaped spokes 8 having bent portions can deform significantly at the bent portions when a ground contact load is applied. By connecting the intermediate ring 9 to the bent portions that deform significantly, stress near the contact point due to the ground contact load can be efficiently transmitted in the circumferential direction.

[0048] The airless tire 1 of the above embodiment has an intermediate ring 9 that transmits loads in the circumferential direction, while the shear layer 10, which is composed of the outer reinforcing layer 11 and the elastomer layer 12, has low shear stiffness. The outer ring 5, which has low shear stiffness, undergoes shear deformation at its circumferential contact edge when a ground load is applied, thereby ensuring a sufficient contact length and area between the tire and the road surface. Here, if the spoke portions 6 have low shear stiffness, they undergo shear deformation at their circumferential contact edge when a ground load is applied, just like the outer ring 5. The shear deformation of the spoke portions 6 also supports the function of the shear layer 10, contributing to ensuring a sufficient contact length and area between the tire and the road surface. Furthermore, because both the spoke portions 6 and the outer ring 5 undergo shear deformation as their primary deformation mode, the shear stress between these layers can also be reduced.

[0049] According to the airless structure of the above embodiment, the shear layer 10 further includes an inner reinforcing layer 13 in contact with the inner circumferential surface of the elastomer layer 12. The Young's modulus of the inner reinforcing layer 13 is lower than that of the outer reinforcing layer 11 (see Examples 2, 4, and 5). Various manufacturing methods for joining the outer ring and spokes of an airless tire have been proposed, but whichever method is used, shear stress occurs at the interface between the outer ring and the spokes, which can cause failures such as peeling. In particular, in the case of a shear layer 10 having only the outer reinforcing layer 11 as a reinforcing layer (see Example 1), the absence of the inner reinforcing layer 13 tends to increase shear stress at the interface between the layers due to the difference in deformation between the outer ring 5 and the spokes 6 compared to conventional techniques. For this reason, when adding the inner reinforcing layer 13 while maintaining the advantages of the structure combining the outer ring 5 with the shear layer 10 and the spokes 6 with the connecting portions 9a, the inner reinforcing layer 13 is added, which has a Young's modulus lower than that of the outer reinforcing layer 11. This makes it possible to prevent failures caused by the interface between the layers of the outer ring 5 and the spoke portion 6.

[0050] Furthermore, according to the airless structure of the above embodiment, the shear layer 10 further includes one or more intermediate reinforcing layers 16 within the elastomer layer 12 between the outer reinforcing layer 11 and the inner reinforcing layer 13. The Young's modulus of the intermediate reinforcing layer 16 is lower than that of the outer reinforcing layer 11 and higher than that of the inner reinforcing layer 13 (see Example 5). If the intermediate reinforcing layer 16 is not provided, the difference in Young's modulus between the outer reinforcing layer 11 and the inner reinforcing layer 13 will be somewhat large. In this case, shear stress generated between the elastomer layer 12 and the reinforcing layer 11 or 13 may cause the reinforcing layer 11 or 13 to peel off. Therefore, by providing the shear layer 10 with multiple reinforcing layers 11, 13, and 16 whose Young's moduli gradually decrease from the radially outer side to the radially inner side, the above-mentioned possibility can be eliminated.

[0051] According to the airless structure of the above embodiment, the radial rigidity of the outer ring 5 alone is 1 / 10 or less of the radial rigidity of the entire airless tire 1. The radial rigidity of the entire airless tire 1 can also be considered to be the sum of the rigidity of the outer ring 5 and the rigidity of the spoke portions 6. To realize the advantages of the structure combining the outer ring 5 having the shear layer 10 with the spoke portions 6 having the connecting portions 9a described above, it is effective to set the radial rigidity of the outer ring 5 alone to 1 / 10 or less of the radial rigidity of the entire airless tire 1. When the above ratio is 1 / 10 or less, it is possible to more reliably achieve both ensuring the contact length and contact area and reducing rolling resistance. When the above ratio is more than 1 / 10, the rigidity of the outer ring 5 becomes high, making it difficult to ensure the contact length and contact area while reducing rolling resistance.

[0052] The longitudinal stiffness of the entire airless tire 1 is defined as the gradient of the radial deflection with respect to the ground load when the airless tire 1 is restrained at its center O (using the wheel 2) and a ground load is applied. The longitudinal stiffness of the outer ring 5 alone is defined as the gradient of the radial deflection with respect to the load when one point on the outer ring 5 is restrained and a load is applied to a point radially opposite to the restrained point.

[0053] While the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and application techniques will become apparent to those skilled in the art from this disclosure. For example, while the airless tire 1 and wheel 2 are separate components in the above embodiment, they may be integrated. In this case, the airless tire 1 would have a hub portion similar to that of the wheel 2 in its center, and the outer periphery of this hub portion would form the inner ring 4. Furthermore, in this case, the metal hub portion may be insert-molded when the spoke portion 6 and outer ring 5 are molded from resin. [Explanation of symbols]

[0054] 1. Airless tires 4 Inner ring 5 outer ring 6 spokes 7 tread layers 8 spokes 9 Intermediate Ring 9a Connecting part 10 Shear Layer 11 Outer reinforcement layer 12 Elastomer layer 13 Inner reinforcement layer 15 Reinforcing Fiber 16 Middle reinforcement layer O (Airless tire 1) Center

Claims

1. An airless tire structure, an inner ring disposed at the center of the airless tire; an outer ring having a tread layer on its outermost periphery; a spoke portion having a plurality of spokes arranged radially between the inner circumferential ring and the outer circumferential ring, connecting the outer periphery of the inner circumferential ring with the inner periphery of the outer circumferential ring; The spoke portion is provided with a connecting portion that connects adjacent spokes to each other in the circumferential direction, the outer ring has a shear layer in contact with an inner circumferential surface of the tread layer, The shear layer has an outer reinforcing layer in contact with the inner circumferential surface of the tread layer, and an elastomer layer disposed inside the outer reinforcing layer.

2. 2. The airless tire structure according to claim 1, An airless tire structure, wherein the connecting portion forms a plurality of intermediate rings concentric with a center of the airless tire.

3. 3. The airless tire structure according to claim 2, Each of the spokes has a zigzag shape when viewed from the rotation axis direction of the airless tire, The intermediate ring is connected to the spokes at the zigzag bends.

4. 2. The airless tire structure according to claim 1, the shear layer further comprises an inner reinforcing layer in contact with an inner peripheral surface of the elastomeric layer; An airless tire structure, wherein the Young's modulus of the inner reinforcing layer is lower than the Young's modulus of the outer reinforcing layer.

5. 5. The airless tire structure according to claim 4, the shear layer further comprises one or more intermediate reinforcing layers within the elastomeric layer between the outer reinforcing layer and the inner reinforcing layer; An airless tire structure, wherein the Young's modulus of the intermediate reinforcing layer is lower than that of the outer reinforcing layer and higher than that of the inner reinforcing layer.

6. The airless tire structure according to any one of claims 1 to 5, An airless tire structure, wherein the radial stiffness of the outer ring alone is 1 / 10 or less of the radial stiffness of the entire airless tire.

Images