Non-pneumatic tires

Abstract

To provide a non-pneumatic tire that can be effectively improved in durability.SOLUTION: The non-pneumatic tire comprises an inside annular part 20, an outside annular part 30, a plurality of spokes 40 connecting the inside annular part 20 to the outside annular part 30, a tread 50. The spoke 40 has a first straight part 410 extending obliquely with respect to a tire axial direction, a first inner connection part 411, and a first outer connection part 412. The first inner connection part 411 has a first inner transfer portion 411b at a side at which an angle formed by the first straight part 410 and the inside annular part 20 is an acute angle, and a second inner transfer portion 411a at a side at which an angle formed by the first straight part 410 and the inside annular part 20 is an obtuse angle. The first inner transfer portion 411b includes a first inner R portion 411R leading in a circular arc shape to the inside annular part 20, where when a curvature radius of the first inner R portion 411R is defined as r and a length of the first straight part 410 is defined as L, r / L is 0.17 or more and 0.24 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a non-pneumatic tire. [Background technology]

[0002] In recent years, non-pneumatic tires have been developed that are free from problems such as punctures and do not require air pressure adjustment. Non-pneumatic tires generally have a structure in which an inner annular portion and an outer annular portion are coaxially arranged and connected by a plurality of spokes. The spokes are arranged radially at intervals around the tire circumference. A tread that comes into contact with the road surface is provided on the outer peripheral surface of the outer annular portion.

[0003] For example, Patent Document 1 discloses a non-pneumatic tire having plate-shaped spokes whose thickness direction is along the tire circumferential direction and which are inclined with respect to the tire axial direction, and the spokes are provided with reinforcing parts to increase durability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-43505 A Summary of the Invention [Problem to be solved by the invention]

[0005] In this type of non-pneumatic tire, a high proportion of the load is placed on the spokes. Spokes that are inclined relative to the tire axial direction tend to concentrate stress at the points where they intersect the inner annular portion at an acute angle, resulting in reduced durability. However, this point is not taken into consideration in Patent Document 1.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a non-pneumatic tire having spokes inclined relative to the tire axial direction, which can effectively improve durability. [Means for solving the problem]

[0007] a tread provided on the outer peripheral surface of the outer annular portion, wherein the spokes have a straight portion extending at an angle with respect to the tire axial direction, an inner connecting portion connecting the straight portion to the inner annular portion, and an outer connecting portion connecting the straight portion to the outer annular portion, and the inner connecting portion has a first inner transition portion on the side where the straight portion forms an acute angle with the inner annular portion, and a second inner transition portion on the side where the straight portion forms an obtuse angle with the inner annular portion, and the first inner transition portion includes an R portion that is connected to the inner annular portion in an arc shape, and wherein r / L is 0.17 or more and 0.24 or less, where r is the radius of curvature of the R portion and L is the length of the straight portion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a non-pneumatic tire having spokes that are inclined with respect to the tire axial direction, which can effectively improve durability. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side view showing a non-pneumatic tire of a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 3] FIG. 3 is a partial perspective view of a non-pneumatic tire, as seen obliquely from the portion shown in FIG. 2. [Figure 4] 10 is a graph showing measurement results of a test example using an analytical model. [Figure 5] FIG. 10 is a diagram schematically illustrating the transition of deformation of an analysis model subjected to a vertical load, illustrating an embodiment of the present invention. [Figure 6] FIG. 10 is a diagram schematically illustrating the transition of deformation of an analysis model subjected to a vertical load, showing a comparative example outside the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, this embodiment will be described with reference to the drawings. Fig. 1 is a side view of a non-pneumatic tire 1 of this embodiment, viewed from the side in a direction parallel to the tire rotation axis (tire meridian), i.e., in a direction along the front-to-back direction of the paper in Fig. 1. The non-pneumatic tire 1 shown in Fig. 1 is in an unloaded state. Fig. 2 is a cross-sectional view taken along II-II in Fig. 1. Fig. 3 is a partial perspective view of the non-pneumatic tire 1, when the portion shown in Fig. 2 is viewed obliquely.

[0011] In Fig. 1 and Fig. 3, arrow C indicates the tire circumferential direction. In Fig. 1 to Fig. 3, arrow X indicates the tire radial direction. In Fig. 2 and Fig. 3, arrow Y indicates the tire width direction. In Fig. 1, the tire width direction Y is the front-to-back direction of the paper. In Fig. 2, symbol E is the tire equatorial plane. In Fig. 2, the tire circumferential direction C is the front-to-back direction of the paper.

[0012] The tire circumferential direction C is a direction around the tire rotational axis and is the same direction as the rotational direction of the non-pneumatic tire 1. The tire radial direction X is a direction perpendicular to the tire rotational axis. The tire width direction Y is a direction parallel to the tire rotational axis. In FIGS. 2 and 3, one side of the tire width direction Y is indicated as Y1, and the other side of the tire width direction Y is indicated as Y2. The tire equatorial plane E shown in FIG. 2 is a plane perpendicular to the tire rotational axis and located at the center of the tire width direction Y.

[0013] The non-pneumatic tire 1 of this embodiment includes an inner annular portion 20, an outer annular portion 30, a plurality of spokes 40, and a tread 50.

[0014] In the following description, the thicknesses of the inner annular portion 20 and the outer annular portion 30 refer to the dimensions in the tire radial direction X. The widths of the inner annular portion 20 and the outer annular portion 30 refer to the dimensions in the tire width direction Y shown in FIG.

[0015] The inner annular portion 20 is an annular portion along the tire circumferential direction C that constitutes the inner circumferential portion of the non-pneumatic tire 1. The thickness and width of the inner annular portion 20 are set to be constant to improve uniformity. A tire wheel (not shown) is placed in the space on the inner circumferential side of the inner annular portion 20. The inner circumferential portion of the inner annular portion 20 is fitted onto the outer circumferential portion of the rim of the tire wheel. The inner annular portion 20 is fitted onto the rim, and the non-pneumatic tire 1 is then fitted onto the tire wheel. The inner circumferential surface of the inner annular portion 20 may be provided with a fitting portion consisting of a protrusion, a groove, etc. for fitting with the rim.

[0016] The inner annular portion 20 can be made of, for example, a resin material having elasticity, but the material is not limited to resin.

[0017] The inner annular portion 20 transmits the rotation of the tire wheel to the spokes 40 and the outer annular portion 30. The thickness of the inner annular portion 20 is determined from the viewpoint of achieving light weight and durability while fulfilling the function of sufficiently transmitting rotational force to the spokes 40. The thickness of the inner annular portion 20 is not particularly limited, but is preferably 2% to 7% of the tire cross-sectional height H shown in Fig. 2, and more preferably 3% to 6%.

[0018] The inner diameter of the inner annular portion 20 is determined depending on the dimensions of the rim of the tire wheel on which the non-pneumatic tire 1 is mounted, the use of the vehicle, etc. For example, when assuming a replacement for a general pneumatic tire, the inner diameter of the inner annular portion 20 may be, for example, a dimension of 250 mm or more and 500 mm or less, but is not limited to this.

[0019] The width of the inner annular portion 20 is determined appropriately depending on the use of the vehicle on which the non-pneumatic tire 1 is mounted, the length of the axle, etc. For example, when assuming a replacement for a general pneumatic tire, the width of the inner annular portion 20 may be, but is not limited to, a dimension of 100 mm or more and 300 mm or less.

[0020] The outer annular portion 30 is an annular portion along the tire circumferential direction C that constitutes the outer periphery of the non-pneumatic tire 1. The outer annular portion 30 is disposed coaxially with the inner annular portion 20 on the outer circumferential side of the inner annular portion 20. The thickness and width of the outer annular portion 30 are set to be constant to improve uniformity.

[0021] The outer annular portion 30 can be made of, for example, an elastic resin material, but the material is not limited to resin.

[0022] The outer annular portion 30 transmits the rotation of the inner annular portion 20 and the spokes 40 to the road surface via the tread 50. The thickness of the outer annular portion 30 is determined from the viewpoint of achieving light weight and durability while also fulfilling the function of sufficiently transmitting rotational force from the spokes 40 to the road surface. The thickness of the outer annular portion 30 is not particularly limited, but is preferably, for example, 2% to 7% of the tire cross-sectional height H shown in FIG. 2, and more preferably 2% to 5%.

[0023] The inner diameter of the outer annular portion 30 is determined appropriately depending on the dimensions of the rim of the tire wheel on which the non-pneumatic tire 1 is mounted, the use of the vehicle, etc. For example, when assuming a replacement for a general pneumatic tire, the inner diameter of the outer annular portion 30 may be, but is not limited to, a dimension of 420 mm or more and 750 mm or less.

[0024] The width of the outer annular portion 30 is determined appropriately depending on the application of the vehicle on which the non-pneumatic tire 1 is mounted, etc. For example, when assuming a replacement for a general pneumatic tire, the width of the outer annular portion 30 may be, but is not limited to, a dimension of 100 mm or more and 300 mm or less.

[0025] The plurality of spokes 40 connect the inner annular portion 20 and the outer annular portion 30. The inner annular portion 20 and the outer annular portion 30, connected by the plurality of spokes 40, are arranged coaxially with each other. The plurality of spokes 40 are arranged independently along the tire circumferential direction C. As shown in FIG. 1 , when the non-pneumatic tire 1 is in an unloaded state, the plurality of spokes 40 extend linearly in the radial direction substantially parallel to the tire radial direction X in a side view. The plurality of spokes 40 are arranged at equal intervals in the tire circumferential direction C.

[0026] 2 and 3, the multiple spokes 40 of this embodiment include multiple first spokes 41 and multiple second spokes 42. The extension direction of both the first spokes 41 and the second spokes 42 is not parallel to the tire radial direction X when viewed in a direction along the tire circumferential direction C. The first spokes 41 are inclined toward one side in the tire axial direction, i.e., the tire width direction Y. The second spokes 42 are inclined toward the opposite side to the first spokes 41. The first spokes 41 and the second spokes 42 are arranged alternately in the tire circumferential direction C.

[0027] 2 and 3, the first spokes 41 generally extend at an incline from the Y1 side, which is one side in the tire width direction Y of the outer annular portion 30, toward the Y2 side, which is the other side in the tire width direction Y of the inner annular portion 20. The second spokes 42 generally extend at an incline from the Y2 side, which is the other side in the tire width direction Y of the outer annular portion 30, toward the Y1 side, which is one side in the tire width direction Y of the inner annular portion 20.

[0028] The inclination angles of the first spokes 41 and the second spokes 42 are the same. Therefore, the first spokes 41 and the second spokes 42 adjacent to each other in the tire circumferential direction C are arranged in a substantially X-shape when viewed from a direction along the tire circumferential direction C. As shown in FIG. 2 , the first spokes 41 and the second spokes 42 are inclined at an angle θ with respect to the tire width direction Y, and the angle θ is preferably, for example, equal to or greater than 39° and equal to or less than 49°.

[0029] 2, when viewed in a direction along the tire circumferential direction C, the first spokes 41 and the second spokes 42 each have the same shape and are symmetrical with respect to the tire equatorial plane E. Therefore, hereinafter, when there is no need to distinguish between the first spokes 41 and the second spokes 42 and they can be described together, the first spokes 41 and the second spokes 42 will be collectively referred to as spokes 40.

[0030] The spokes 40 are plate-shaped and extend obliquely at the angle θ from the inner annular portion 20 toward the outer annular portion 30 as described above. As shown in FIG. 3 , the thickness t of the spokes 40 along the tire circumferential direction is smaller than the width w, and the direction of the thickness t is along the tire circumferential direction C. That is, the spokes 40 are formed in a plate shape extending in the plane of the tire radial direction X and the tire width direction Y. Note that the width w here refers to the width of a first straight portion 410 and a second straight portion 420, which will be described later, and is the dimension in a direction perpendicular to the oblique direction in which the spokes 40 extend when viewed from the direction along the tire circumferential direction C, as also shown in FIG. 2 . In this embodiment, all of the spokes 40 have the same thickness t. All of the spokes 40 also have the same width w.

[0031] Because the spokes 40 are long and plate-shaped, the durability of the spokes 40 can be improved by widening the plate width w even if the plate thickness t is thin. Furthermore, by thinning the plate thickness t and increasing the number of spokes 40, the distance between adjacent spokes 40 in the tire circumferential direction C can be reduced while maintaining the rigidity of the entire non-pneumatic tire 1. This distributes the ground contact pressure of the spokes 40 when the tire rolls, thereby reducing the ground contact pressure.

[0032] Although the spokes 40 in this embodiment are parallel to the tire radial direction X in a side view, the spokes 40 may be disposed obliquely with respect to the tire radial direction X so as to intersect with the tire radial direction X in a side view.

[0033] The first spoke 41 and the second spoke 42 will now be described in detail with reference to FIGS.

[0034] The first spoke 41 has a first straight portion 410, a first inner connection portion 411 connecting the first straight portion 410 to the inner annular portion 20, and a first outer connection portion 412 connecting the first straight portion 410 to the outer annular portion 30. The first straight portion 410 is an example of a straight portion of the spoke 40 in this embodiment. The first inner connection portion 411 is an example of an inner connection portion of the spoke 40 in this embodiment. The first outer connection portion 412 is an example of an outer connection portion of the spoke 40 in this embodiment. The first inner connection portion 411 is provided in a half region of the inner annular portion 20 on the tire width direction Y2 side. The first outer connection portion 412 is provided in a half region of the outer annular portion 30 on the tire width direction Y1 side.

[0035] The first straight portion 410 extends obliquely from the tire width direction Y1 side of the outer annular portion 30 toward the tire width direction Y2 side of the inner annular portion 20. In other words, the first straight portion 410 coincides with the inclination direction of the first spokes 41.

[0036] The first inner connecting portion 411 has a first inner transition portion 411b that is disposed on the inner side in the tire width direction Y and transitions from the first straight portion 410 to the inner annular portion 20, and a second inner transition portion 411a that is disposed on the outer side in the tire width direction Y and transitions from the first straight portion 410 to the inner annular portion 20. The first inner transition portion 411b is a transition portion that is disposed on the side where the angle formed between the first straight portion 410 and the inner annular portion 20 is an acute angle. The second inner transition portion 411a is a transition portion that is disposed on the side where the angle formed between the first straight portion 410 and the inner annular portion 20 is an obtuse angle.

[0037] The first inner transition portion 411b is disposed on the tire width direction Y1 side (tire equatorial plane E side). The first inner transition portion 411b includes a first inner curved portion 411R that continues in a concave arc shape toward the tire width direction Y1 side from the first straight portion 410 to the position of the tire equatorial plane E of the inner annular portion 20. The first inner curved portion 411R is formed in an arc shape with a curvature radius r. The first inner curved portion 411R is a portion included in the first inner transition portion 411b in this embodiment, and is an example of a curved portion that continues in an arc shape with the inner annular portion 20.

[0038] The second inner transition portion 411a is disposed on the tire width direction Y2 side. The second inner transition portion 411a extends while gently curving to the end portion 20b of the inner annular portion 20 on the tire width direction Y2 side.

[0039] Due to the first inner transition portion 411b and the second inner transition portion 411a, the first inner connecting portion 411 has a shape that widens in the tire width direction Y as it approaches the inner annular portion 20.

[0040] The first outer connection portion 412 has a first outer transition portion 412b that is disposed on the inner side in the tire width direction Y and transitions from the first straight portion 410 to the outer annular portion 30, and a second outer transition portion 412a that is disposed on the outer side in the tire width direction Y and transitions from the first straight portion 410 to the outer annular portion 30. The first outer transition portion 412b is a transition portion that is disposed on the side where the angle formed between the first straight portion 410 and the outer annular portion 30 is an acute angle. The second outer transition portion 412a is a transition portion that is disposed on the side where the angle formed between the first straight portion 410 and the outer annular portion 30 is an obtuse angle.

[0041] The first outer transition portion 412b is disposed on the tire width direction Y2 side (tire equatorial plane E side). The first outer transition portion 412b includes a first outer R portion 412R that continues in a concave arc shape toward the tire width direction Y2 side from the first straight portion 410 to the position of the tire equatorial plane E of the outer annular portion 30. The first outer R portion 412R is formed in an arc shape with a curvature radius r, similar to the first inner R portion 411R.

[0042] The second outer transition portion 412a is disposed on the tire width direction Y1 side. The second outer transition portion 412a extends while gently curving to the end portion 30a of the outer annular portion 30 on the tire width direction Y1 side.

[0043] Due to the first outer transition portion 412b and the second outer transition portion 412a, the first outer connecting portion 412 has a shape that widens in the tire width direction Y as it approaches the outer annular portion 30.

[0044] The first straight portion 410 of the first spoke 41 refers to a region in the tire radial direction having a portion where both side surfaces facing the tire width direction Y are straight. In other words, the first straight portion 410 is a portion that includes both the straight side surfaces between the first inner transition portion 411b of the first inner connecting portion 411 and the second outer transition portion 412a of the first outer connecting portion 412, and the straight side surfaces between the second inner transition portion 411a of the first inner connecting portion 411 and the first outer transition portion 412b of the first outer connecting portion 412.

[0045] The second spokes 42 have the same shape as the first spokes 41 and are symmetrical to the first spokes 41 with respect to the tire equatorial plane E.

[0046] As shown in FIGS. 2 and 3 , the second spoke 42 has a second straight portion 420, a second inner connection portion 421 connecting the second straight portion 420 to the inner annular portion 20, and a second outer connection portion 422 connecting the second straight portion 420 to the outer annular portion 30. The second straight portion 420 is an example of a straight portion of the spoke 40 in this embodiment. The second inner connection portion 421 is an example of an inner connection portion of the spoke 40 in this embodiment. The second outer connection portion 422 is an example of an outer connection portion of the spoke 40 in this embodiment. The second inner connection portion 421 is provided in a half region of the inner annular portion 20 on the tire width direction Y1 side. The second outer connection portion 422 is provided in a half region of the outer annular portion 30 on the tire width direction Y2 side.

[0047] The second straight portion 420 extends obliquely from the tire width direction Y2 side of the outer annular portion 30 toward the tire width direction Y1 side of the inner annular portion 20. In other words, the second straight portion 420 coincides with the inclination direction of the second spokes 42.

[0048] The second inner connecting portion 421 has a first inner transition portion 421b that is disposed on the inner side in the tire width direction Y and transitions from the second straight portion 420 to the inner annular portion 20, and a second inner transition portion 421a that is disposed on the outer side in the tire width direction Y and transitions from the second straight portion 420 to the inner annular portion 20. The first inner transition portion 421b is a transition portion that is disposed on the side where the angle formed between the second straight portion 420 and the inner annular portion 20 is an acute angle. The second inner transition portion 421a is a transition portion that is disposed on the side where the angle formed between the second straight portion 420 and the inner annular portion 20 is an obtuse angle.

[0049] The first inner transition portion 421b is disposed on the tire width direction Y2 side (tire equatorial plane E side). The first inner transition portion 421b includes a second inner curved portion 421R that continues in a concave arc shape toward the tire width direction Y2 side from the second straight portion 420 to the position of the tire equatorial plane E of the inner annular portion 20. The second inner curved portion 421R is formed in an arc shape with a curvature radius r. The second inner curved portion 421R is a portion included in the first inner transition portion 421b in this embodiment, and is an example of a curved portion that continues in an arc shape with the inner annular portion 20.

[0050] The second inner transition portion 421a is disposed on the tire width direction Y1 side. The second inner transition portion 421a extends while gently curving to the end portion 20a of the inner annular portion 20 on the tire width direction Y1 side.

[0051] Due to the first inner transition portion 421b and the second inner transition portion 421a, the second inner connecting portion 421 has a shape that widens in the tire width direction Y as it approaches the inner annular portion 20.

[0052] The second outer connection portion 422 has a first outer transition portion 422b that is disposed on the inner side in the tire width direction Y and transitions from the second straight portion 420 to the outer annular portion 30, and a second outer transition portion 422a that is disposed on the outer side in the tire width direction Y and transitions from the second straight portion 420 to the outer annular portion 30. The first outer transition portion 422b is a transition portion that is disposed on the side where the angle formed between the second straight portion 420 and the outer annular portion 30 is an acute angle. The second outer transition portion 422a is a transition portion that is disposed on the side where the angle formed between the second straight portion 420 and the outer annular portion 30 is an obtuse angle.

[0053] The first outer transition portion 422b is disposed on the tire width direction Y1 side (tire equatorial plane E side). The first outer transition portion 422b includes a second outer R portion 422R that continues in a concave arc shape toward the tire width direction Y1 side from the second straight portion 420 to the position of the tire equatorial plane E of the outer annular portion 30. The second outer R portion 422R is formed in an arc shape with a curvature radius r, similar to the second inner R portion 421R.

[0054] The second outer transition portion 422a is disposed on the tire width direction Y2 side. The second outer transition portion 422a extends while gently curving to the end portion 30b of the outer annular portion 30 on the tire width direction Y2 side.

[0055] Due to the first outer transition portion 422b and the second outer transition portion 422a, the second outer connecting portion 422 has a shape that widens in the tire width direction Y as it approaches the outer annular portion 30.

[0056] The second straight portion 420 of the second spoke 42 refers to a region in the tire radial direction having a portion where both side surfaces facing the tire width direction Y are straight. In other words, the second straight portion 420 is a portion that includes both the straight side surfaces between the first inner transition portion 421b of the second inner connection portion 421 and the second outer transition portion 422a of the second outer connection portion 422, and the straight side surfaces between the second inner transition portion 421a of the second inner connection portion 421 and the first outer transition portion 422b of the second outer connection portion 422.

[0057] The radii of curvature r of the first inner R portion 411R of the first spoke 41 and the second inner R portion 421R of the second spoke 42 are equal to each other. The lengths L of the first straight portion 410 of the first spoke 41 and the second straight portion 420 of the second spoke 42 are also equal to each other. The lengths L of the first straight portion 410 and the second straight portion 420 refer to the lengths of straight lines passing through the widthwise centers of the board width w in the first straight portion 410 and the second straight portion 420.

[0058] In this embodiment, the ratio of r to L, r / L, is preferably 0.17 or more and 0.24 or less, and more preferably 0.192 or more and 0.207 or less.

[0059] In this embodiment, the radius of curvature r of each of the first inner R portion 411R and the second inner R portion 421R is preferably 7.3 mm or more and 9.0 mm or less, and more preferably 7.8 mm or more and 8.3 mm or less. In this embodiment, the length L of the first straight portion 410 and the second straight portion 420 is preferably 39.4 mm or more and 41.2 mm or less, and more preferably 40.0 mm or more and 40.6 mm or less.

[0060] As described above, in this embodiment, all of the spokes 40 have the same thickness t. The dimension of the thickness t is not particularly limited, but is preferably 1 mm or more and 30 mm or less, and more preferably 5 mm or more and 25 mm or less, so that the spokes 40 can sufficiently withstand the rotational force from the inner annular portion 20 and the outer annular portion 30 and can be appropriately flexibly deformed when subjected to a load.

[0061] As described above, all spokes 40 in this embodiment have the same width w. The width w of the spokes 40 is the width of the first straight portion 410 and the second straight portion 420. The width w of the spokes 40 is not particularly limited, but is preferably 5 mm or more and 25 mm or less, and more preferably 10 mm or more and 20 mm or less, so as to be able to adequately withstand rotational forces from the inner annular portion 20 and the outer annular portion 30 while being able to flex and deform appropriately when subjected to a load. Furthermore, the width w is preferably 110% or more of the thickness t, and more preferably 115% or more, from the viewpoint of being able to distribute ground pressure while improving durability.

[0062] 2, the width w2 of the spokes 40 at the connection ends to the inner annular portion 20 and the outer annular portion 30 in the tire width direction Y is the same and is preferably 30 mm to 140 mm, more preferably 70 mm to 140 mm. In this embodiment, it is half the dimension of the inner annular portion 20 and the outer annular portion 30 in the tire width direction Y.

[0063] The number of spokes 40 is preferably 80 to 300, and more preferably 100 to 200, from the viewpoint of being able to adequately support the load from the vehicle while being lightweight and achieving both improved power transmission and durability.

[0064] The intervals between the spokes 40 in the tire circumferential direction C are preferably set to, for example, 1.0 mm or more and 4.1 mm or less. In this embodiment, the intervals between the spokes 40 in the tire circumferential direction C are equal, but may be unequal.

[0065] The dimension of the spoke 40 in the tire radial direction X is, for example, 45 mm or more and 75 mm or less, but is not limited to this.

[0066] The spokes 40 can be made of the following elastic materials. First, in terms of the properties of the elastic material, from the viewpoint of providing adequate rigidity while ensuring sufficient durability, a tensile test is carried out in accordance with JIS K7312, and the tensile strength is calculated from the tensile stress at 10% elongation. The modulus is preferably 3 MPa or more and 12 MPa or less.

[0067] If the tensile modulus of the spokes 40 calculated from the tensile stress at 10% elongation is less than 3 MPa, sufficient rigidity cannot be obtained, and there is a possibility that adjacent spokes 40 in the tire circumferential direction C may come into contact with each other. On the other hand, if the tensile modulus calculated from the tensile stress at 10% elongation exceeds 12 MPa, the rigidity becomes excessively high, resulting in a deterioration in ride comfort.

[0068] The elastic material used as the base material of the spokes 40 may be a thermoplastic elastomer, a crosslinked rubber, or other resin.

[0069] Examples of thermoplastic elastomers include polyester elastomers, polyolefin elastomers, polyamide elastomers, polystyrene elastomers, polyvinyl chloride elastomers, and polyurethane elastomers.

[0070] The rubber material constituting the crosslinked rubber can be either natural rubber or synthetic rubber. Examples of synthetic rubber include styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IIR), nitrile rubber (NBR), hydrogenated nitrile rubber (hydrogenated NBR), chloroprene rubber (CR), ethylene propylene rubber (EPDM), fluororubber, silicone rubber, acrylic rubber, and urethane rubber. Two or more of these rubber materials may be used in combination as needed.

[0071] Other resins include thermoplastic resins and thermosetting resins. Thermoplastic resins include polyethylene resins, polystyrene resins, polyvinyl chloride resins, etc. Thermosetting resins include epoxy resins, phenolic resins, polyurethane resins, silicone resins, polyimide resins, melamine resins, etc.

[0072] Of the above elastic materials, polyurethane resin is preferably used for the spokes 40 from the viewpoints of moldability, processability, and cost. However, foamed materials can also be used as the elastic material. That is, foamed materials made from the above thermoplastic elastomers, crosslinked rubbers, and other resins can be used.

[0073] The elastic material used as the base material of the spokes 40 may be reinforced with reinforcing fibers. Examples of reinforcing fibers include long fibers, short fibers, woven fabrics, and nonwoven fabrics. Examples of reinforcing fibers include rayon cords, polyamide cords such as nylon-6,6, polyester cords such as polyethylene terephthalate, aramid cords, glass fiber cords, carbon fibers, and steel cords.

[0074] The reinforcement of the elastic material is not limited to reinforcement with reinforcing fibers. For example, reinforcement may be performed by adding granular fillers. Examples of the granular fillers that can be added include carbon black, ceramics such as silica and alumina, and other inorganic fillers.

[0075] Incidentally, it is preferable that the inner annular portion 20 and the outer annular portion 30 are formed from the same resin material as the spokes 40. In this case, the inner annular portion 20, the outer annular portion 30 and the spokes 40 can be integrally molded, for example, by a casting molding method.

[0076] The tread 50 is provided on the outer peripheral surface of the outer annular portion 30 . The tread 50 forms the outermost peripheral portion of the non-pneumatic tire 1. The tread 50 includes tread rubber 51. The tread rubber 51 has a tread surface 51a on its outer peripheral surface that comes into contact with the road surface. There are no particular restrictions on the type of rubber material for the tread rubber 51, and general vulcanized rubber, etc., used for forming the tread of a vehicle tire, can be used. The tread surface 51a of the tread rubber 51 is provided with a tread pattern formed of a plurality of grooves and land portions, similar to that of a conventional pneumatic tire. The tread rubber 51 may have a structure in which a plurality of rubber layers with different components or properties are laminated (for example, two or three layers). The tread 50 may also be made of resin.

[0077] The non-pneumatic tire 1 of the present embodiment may further include a reinforcing layer (not shown). The reinforcing layer may be embedded in the outer annular portion 30. Alternatively, the reinforcing layer may be provided between the outer annular portion 30 and the tread 50. The reinforcing layer is a cylindrical layer extending along the tire circumferential direction C.

[0078] The reinforcing layer is arranged evenly around the entire circumference of the tire to suppress the occurrence of buckling, in which the outer annular portion 30 bends in the tire radial direction X at the center in the tire width direction Y. The reinforcing layer is configured, for example, by arranging steel cords so that they are generally parallel to the tire width direction Y. The reinforcing layer may be a cylindrical metal ring, a high-modulus resin ring, or the like. For example, the reinforcing layer may be a ring made of fiber-reinforced plastic (FRP), such as carbon fiber-reinforced plastic (CFRP) or glass fiber-reinforced plastic (GFRP). By providing the reinforcing layer, the rigidity of the non-pneumatic tire 1 is ensured, and the contact of the tread 50 with the road surface is improved. [Example]

[0079] When stress distribution was examined when a longitudinal load was applied to the spokes of an FEM analysis model with a configuration similar to that shown in Figures 1 to 3, it was found that the highest stress value was found in the inner curved portion (first inner curved portion 411R or second inner curved portion 421R) that underwent compressive deformation. The longitudinal load is a load that the spoke receives in a direction generally along its length, from top to bottom, at the portion that comes into contact with the road surface. Therefore, using an analysis model, the stress value when stress is applied to the inner curved portion of the spoke and compresses it, as well as the longitudinal rigidity of the spoke, were measured by simulation. Table 1 shows the radius of curvature r of the inner curved portion, the length L of the straight portion of the spoke 40, and r / L for Test Examples 1 to 11, which are the analysis models. The measurement results are also shown in Table 1 and graphed as shown in Figure 4. In each of Test Examples 1 to 11, the inner curved portion and the outer curved portion had the same radius of curvature. Furthermore, the tire cross-sectional height H, plate thickness t, and plate width w of the spokes were the same for Test Examples 1 to 11.

[0080] The stress value generated in the inner R portion indicates the degree of stress concentration due to compression, and the lower the value, the better from the standpoint of durability. Therefore, the lower the "Stress value / Target stress value" in Table 1, the better. Furthermore, the vertical stiffness indicates the degree of stiffness when the spoke in the part that comes into contact with the road surface is subjected to a vertical load from above to below in the approximate lengthwise direction, and the lower the value, the better from the standpoint of ride comfort. Therefore, the lower the "Vertical stiffness / Target vertical stiffness" in Table 1, the better.

[0081] [Table 1]

[0082] According to Table 1 and Figure 4, in Test Examples 3 to 11 where r / L exceeds 0.17, the stress value of the inner R portion is below the target value, reducing stress concentration in the inner R portion. On the other hand, when r / L exceeds 0.23, the vertical rigidity exceeds the target value, raising concerns about a decrease in ride comfort. As is clear from Figure 4, when r / L is in the range of 0.192 to 0.207, the stress value tends to temporarily decrease in some areas compared to the lower and upper ends of this range. When r / L is in this range, both the stress value and vertical rigidity can be achieved at low values.

[0083] Figure 5 shows the second spoke 42 of the analysis model of Test Example 6, with the left side showing the second spoke 42 before receiving a vertical load and the right side showing the second spoke 42 in a state where the vertical load is being applied. Figure 6 shows the second spoke 42 of the analysis model of Test Example 1, with the left side showing the second spoke 42 before receiving a vertical load and the right side showing the second spoke 42 in a state where the vertical load is being applied.

[0084] In Test Example 1 shown in Figure 6, the stress value of the second inner R portion 421R is higher than in Test Example 6 shown in Figure 5. This is presumably because part of the compressive deformation region of the second inner R portion 421R overlaps with part of the substantially S-shaped deformation region of the second straight portion 420, which tends to concentrate stress on the second inner R portion 421R, resulting in a higher stress value in the second inner R portion 421R. In contrast, in Test Example 6, r / L is within the specified value, so the deformation of the second spoke 42 does not reach the second inner R portion 421R, which reduces the degree of compressive deformation of the second inner R portion 421R and therefore the stress value.

[0085] From the results of the examples, in the above embodiment, r / L is 0.17 or more and 0.24 or less, so vertical rigidity is ensured and stress concentration on the first inner R portion 411R of the first spoke 41 and the second inner R portion 421R of the second spoke 42 is reduced, thereby effectively improving tire durability.

[0086] The non-pneumatic tire 1 of this embodiment provides the following effects.

[0087] (1) A non-pneumatic tire 1 according to this embodiment includes an inner annular portion 20, an outer annular portion 30 arranged coaxially with the inner annular portion 20 on the outer peripheral side of the inner annular portion 20, first spokes 41 and second spokes 42 as a plurality of spokes 40 that connect the inner annular portion 20 and the outer annular portion 30 and are arranged along the tire circumferential direction C, and a tread 50 provided on the outer peripheral surface of the outer annular portion 30, and the spokes 40 include a first linear portion 410 or a second linear portion 420 as a linear portion that extends at an angle with respect to the tire axial direction, a first inner connecting portion 411 or a second inner connecting portion 421 as an inner connecting portion that connects the linear portion and the outer annular portion, and a first outer connecting portion 422 as an outer connecting portion that connects the linear portion and the outer annular portion. 12 or a second outer connection portion 422, and the inner connection portion has a first inner transition portion 411b or a first inner transition portion 421b on the side where the angle between the straight portion and the inner annular portion 20 is an acute angle, and a second inner transition portion 411a or a second inner transition portion 421a on the side where the angle between the straight portion and the inner annular portion 20 is an obtuse angle, and the first inner transition portion 411b and the first inner transition portion 421b each include a first inner R portion 411R and a second inner R portion 421R that are continuous in an arc with the inner annular portion 20, and where the radius of curvature of the first inner R portion 411R and the second inner R portion 421R is r and the length of the first straight portion 410 and the second straight portion 420 is L, r / L is 0.17 or more and 0.24 or less.

[0088] This reduces the concentration of stress on the first inner R portion 411R of the first spoke 41 and the second inner R portion 421R of the second spoke 42, effectively improving the durability of the tire.

[0089] (2) In the non-pneumatic tire 1 according to this embodiment, it is preferable that the radius of curvature r of each of the first inner R portion 411R of the first spoke 41 and the second inner R portion 421R of the second spoke 42 is equal to or greater than 7.3 mm and equal to or less than 9.0 mm.

[0090] This makes it easy to set r / L to 0.17 or more and 0.24 or less, thereby reducing stress concentration on the first inner R portion 411R of the first spoke 41 and the second inner R portion 421R of the second spoke 42, effectively improving tire durability.

[0091] (3) In the non-pneumatic tire 1 according to this embodiment, the length L of each of the first straight portion 410 of the first spoke 41 and the second straight portion 420 of the second spoke 42 is preferably 39.4 mm or more and 41.2 mm or less.

[0092] This makes it easy to set r / L to 0.17 or more and 0.24 or less, thereby reducing stress concentration on the first inner R portion 411R of the first spoke 41 and the second inner R portion 421R of the second spoke 42, effectively improving tire durability.

[0093] (4) In the non-pneumatic tire 1 according to this embodiment, the spokes 40 preferably include a first spoke 41 whose first straight portion 410 is inclined toward one side of the tire axial direction and a second spoke 42 whose second straight portion 420 is inclined toward the opposite side of the first spoke 41, and the first spokes 41 and the second spokes 42 are arranged alternately in the tire circumferential direction C.

[0094] As a result, the first spokes 41 and the second spokes 42 are arranged in a substantially X-shape when viewed from a direction along the tire circumferential direction C. Because the first spokes 41 and the second spokes 42 are each inclined toward the tire axial direction, excessive rigidity is prevented, thereby improving ride comfort.

[0095] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and improvements made within the scope of the present invention are also included within the scope of the present invention. For example, the spoke 40 in the embodiment includes a first spoke 41 and a second spoke 42 that intersect in an approximately X-shape when viewed from a direction along the tire circumferential direction C, but the spoke 40 is not limited to this and may be composed of a plate-shaped portion that extends straight in the tire radial direction X. [Explanation of symbols]

[0096] 1 Non-pneumatic tires 20 Inner annular portion 30 Outer annular part 40 spokes 41 First Spoke 42 Second Spoke 50 tread 410 First straight section (straight section) 411 First inner connector (inner connector) 411a, 421a Second inner transition 411b, 421b First inner transition portion 411R First inner R section (R section) 412 First outer connection part (outer connection part) 420 Second straight section (straight section) 421 Second inner connection (inner connection) 421R Second inner R section (R section) 422 Second outer connection (outer connection) C Circumferential direction of tire Y Tire width direction

Claims

1. an inner annular portion; an outer annular portion disposed coaxially on the outer circumferential side of the inner annular portion; a plurality of spokes that connect the inner annular portion and the outer annular portion and are arranged along the tire circumferential direction; a tread provided on an outer peripheral surface of the outer annular portion, the spokes each have a straight portion extending obliquely with respect to the tire axial direction, an inner connection portion connecting the straight portion and the inner annular portion, and an outer connection portion connecting the straight portion and the outer annular portion, the inner connection portion has a first inner transition portion on a side where the angle formed between the linear portion and the inner annular portion is an acute angle, and a second inner transition portion on a side where the angle formed between the linear portion and the inner annular portion is an obtuse angle, the first inner transition portion includes an R portion that is continuous in an arc shape with the inner annular portion, A non-pneumatic tire, wherein r / L is 0.17 or more and 0.24 or less, where r is the radius of curvature of the R portion and L is the length of the straight portion.

2. The non-pneumatic tire according to claim 1 , wherein the radius of curvature r is equal to or greater than 7.3 mm and equal to or less than 9.0 mm.

3. The non-pneumatic tire according to claim 1 or 2, wherein the length L of the straight portion is equal to or greater than 39.4 mm and equal to or less than 41.2 mm.

4. The spokes are a first spoke, the straight portion of which is inclined toward one side in the tire axial direction; a second spoke, the straight portion of which is inclined in an opposite direction to the first spoke; The non-pneumatic tire according to any one of claims 1 to 3, wherein the first spokes and the second spokes are arranged alternately in the tire circumferential direction.

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