Non-pneumatic tire

Abstract

A non-pneumatic tire 1 comprises: an inner cylinder body; an outer cylinder body 12 surrounding the inner cylinder body from the outward side in a tire radial direction; an elastically deformable coupling member 13 that couples the inner cylinder body and the outer cylinder body 12 to each other; and a tread member 14 provided on the outer circumferential surface of the outer cylinder body 12. An outer circumferential surface 14f of the tread member 14 assumes the shape of a curve that bows outward in the tire radial direction in a cross-sectional view along a tire width direction. The curve is a series of a plurality of arcs AC1 to AC3 with mutually different radii of curvature. The radii of curvature R1 to R3 of the plurality of arcs AC1 to AC3 are such that the farther outward an arc is in the tire width direction on the outer circumferential surface 14f of the tread member 14, the smaller the radius of curvature is.

Description

Non-pneumatic tires

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

[0002] In order to solve the problem of punctures, which is an unavoidable issue with conventional pneumatic tires, non-pneumatic tires have been proposed in recent years. For example, Patent Document 1 discloses a non-pneumatic tire including an inner cylindrical body, an outer cylindrical body surrounding the inner cylindrical body from the outside in the tire radial direction, an elastically deformable connecting member connecting the inner cylindrical body and the outer cylindrical body to each other, and a tread (tread member) fitted onto the outer cylindrical body.

[0003] JP 2024-57476 A

[0004] However, in a non-pneumatic tire such as that described in Patent Document 1, the rigidity of the outer cylinder is very high and the amount of deformation is small. Therefore, for example, if the outer peripheral surface of the tread member is formed in a straight line (flat) or an arc shape with a large radius of curvature when viewed in cross section along the tire width direction, it has been found that if a slip angle or camber angle is created while the vehicle is traveling, the ground contact pressure in the shoulder portion of the tread member will be locally high, which may reduce maneuverability and make the shoulder portion more susceptible to uneven wear.

[0005] Therefore, an object of the present invention is to provide a non-pneumatic tire that can suppress the deterioration of maneuverability and the occurrence of uneven wear in the shoulder portions of the tread members.

[0006] The means for achieving the above objectives are as follows:

[0007] (1) A non-pneumatic tire of the present invention comprises an inner cylindrical body, an outer cylindrical body surrounding the inner cylindrical body from the outside in the tire radial direction, an elastically deformable connecting member connecting the inner cylindrical body and the outer cylindrical body to each other, and a tread member provided on the outer peripheral surface of the outer cylindrical body, wherein the outer peripheral surface of the tread member has a curved shape that is convex outward in the tire radial direction in a cross-sectional view in the tire width direction, the curve is a series of multiple arcs with different radii of curvature, and the radii of curvature of the multiple arcs are smaller as the arcs on the outer peripheral surface of the tread member are closer to the outside in the tire width direction.

[0008] According to the present invention, it is possible to provide a non-pneumatic tire that can suppress deterioration in maneuverability and occurrence of uneven wear in shoulder portions of tread members.

[0009] Fig. 4 is a side view of a non-pneumatic tire according to one embodiment of the present invention. Fig. 5 is a side view showing an example of a tire-rim assembly using the non-pneumatic tire of Fig. 1. Fig. 6 is a perspective view of the non-pneumatic tire of Fig. 1. Fig. 7 is a cross-sectional view taken along line A-A of Fig. 1. Fig. 8 is an enlarged cross-sectional view taken between B-B of Fig. 4.

[0010] The non-pneumatic tire according to the present invention can be mounted on any type of vehicle and is particularly suitable for mounting on, for example, bicycles, motorcycles, automobiles including light vehicles, and handle-type electric wheelchairs.

[0011] Hereinafter, embodiments of a non-pneumatic tire according to the present invention will be described with reference to the drawings. Common components and parts in each drawing are designated by the same reference numerals. In this specification, the "tire width direction" refers to a direction parallel to the central axis O, which is the axis of rotation of the non-pneumatic tire 1, the "tire circumferential direction" refers to a direction circumferential around the central axis O as viewed from the tire width direction, and the "tire radial direction" refers to a direction perpendicular to the central axis O. In some drawings, the tire width direction is indicated by the reference numeral "WD," the tire circumferential direction is indicated by the reference numeral "CD," and the tire radial direction is indicated by the reference numeral "RD." In this specification, the side closer to the tire width center CL (i.e., the center of the tire width direction of a non-pneumatic tire, also commonly referred to as the tire equatorial plane) along the tire width direction is referred to as the "inner side in the tire width direction," and the side farther from the tire width center CL along the tire width direction is referred to as the "outer side in the tire width direction." Furthermore, in this specification, the side closer to the center axis O along the tire radial direction is referred to as the "inner side in the tire radial direction," and the side farther from the center axis O along the tire radial direction is referred to as the "outer side in the tire width direction."

[0012] Figures 1 and 3 to 5 are drawings for explaining a non-pneumatic tire according to one embodiment of the present invention. Figure 1 is a side view of the non-pneumatic tire according to one embodiment of the present invention, Figure 3 is a perspective view of the non-pneumatic tire of Figure 1, Figure 4 is a cross-sectional view taken along line A-A of Figure 1, and Figure 5 is an enlarged cross-sectional view of the section B-B of Figure 4. Also, Figure 2 is a side view showing an example of a tire-rim assembly using the non-pneumatic tire of Figure 1.

[0013] 1 is mounted on a rim 2 to form a tire-rim assembly 3 as shown in Fig. 2, and the tire-rim assembly 3 is attached to an axle of a vehicle (not shown) via the rim 2 by, for example, bolts threaded into bolt holes 2a of the rim 2. In other words, the non-pneumatic tire 1 is attached to the axle of a vehicle via the rim 2 and is put into use.

[0014] Here, in this embodiment, the non-pneumatic tire 1 is formed in an annular shape, the rim 2 to which the non-pneumatic tire 1 is attached is formed in a disk shape, and the central axis of the rim 2 is configured to coincide with the central axis O of the non-pneumatic tire 1. Also, in this embodiment, the center CL of the non-pneumatic tire 1 in the tire width direction is configured to coincide with the center of the rim 2 to which the non-pneumatic tire 1 is attached.

[0015] The non-pneumatic tire 1 has a function of absorbing vibrations transmitted from the ground to the axle, and the rim 2 has a function of connecting the axle and the non-pneumatic tire 1. The non-pneumatic tire 1 and the rim 2 may be made of different materials. For example, the non-pneumatic tire 1 may be made of a material with a relatively low elastic modulus to ensure vibration absorption performance, and the rim 2 may be made of a material with a higher elastic modulus than the non-pneumatic tire 1 to ensure robustness. Furthermore, for example, the rim 2 may be made of a material with a relatively low specific gravity to reduce the weight of the entire tire-rim assembly 3.

[0016] In this embodiment, as shown in Figures 1 to 3, the non-pneumatic tire 1 includes an inner cylindrical body 11, an outer cylindrical body 12 that surrounds the inner cylindrical body 11 from the outside in the tire radial direction, an elastically deformable connecting member 13 that connects the inner cylindrical body 11 and the outer cylindrical body 12 to each other, and a tread member 14 provided on the outer peripheral surface of the outer cylindrical body 12.

[0017] The elastic modulus of the material forming the inner cylindrical body 11, the outer cylindrical body 12, and the connecting member 13 can be, for example, 100 MPa or more and 1500 MPa or less.

[0018] In this embodiment, the inner cylindrical body 11 is attached to the axle via the rim 2, as shown in FIG. 2 . Also, in this embodiment, the outer cylindrical body 12 surrounds the inner cylindrical body 11 from the outside in the tire radial direction, as shown in FIGS. 1 to 3 . That is, the outer cylindrical body 12 surrounds the periphery of the inner cylindrical body 11 from the outside in the tire radial direction. The central axes of the inner cylindrical body 11 and the outer cylindrical body 12 are arranged coaxially with the central axis O. In this embodiment, the inner cylindrical body 11, the outer cylindrical body 12, and the connecting member 13 are arranged with their respective centers in the tire width direction aligned with each other. In this embodiment, the inner cylindrical body 11, the outer cylindrical body 12, and the connecting member 13 are integrally formed from a thermoplastic resin. This allows the non-pneumatic tire 1 to be formed by injection molding, making it suitable for mass production. The thermoplastic resin may be, for example, a single resin, a mixture containing two or more resins, or a mixture containing one or more resins and one or more elastomers, and may further contain additives such as antioxidants, plasticizers, fillers, or pigments. The inner cylindrical body 11, the outer cylindrical body 12, and the connecting member 13 may be formed separately from each other. The inner cylindrical body 11, the outer cylindrical body 12, and the connecting member 13 may also be formed from a material other than a thermoplastic resin.

[0019] In this embodiment, as shown in FIGS. 1 and 2 , a plurality of connecting members 13 are arranged between the inner cylindrical body 11 and the outer cylindrical body 12, so as to be point-symmetrical with respect to each other with respect to the central axis O. Adjacent connecting members 13 in the tire circumferential direction are arranged spaced apart and not in contact with each other. As shown in the figures, the connecting member 13 has a curved shape in side view, and two portions 13 a, 13 c with a small inclination angle relative to the tire radial direction are connected by a portion 13 b with a large inclination angle relative to the tire radial direction. As a result, the tire radially inner end of the portion 13 a connected to the inner cylindrical body 11 is located on one side of the tire radially outer end of the portion 13 c connected to the outer cylindrical body 12. This allows the connecting member 13 to be used as a leaf spring that easily elastically deforms in the tire radial direction.

[0020] In this embodiment, as shown in each drawing, the tread element 14 is provided on the outer peripheral surface of the outer cylindrical body 12. More specifically, in this embodiment, the tread element 14 is provided so as to cover the entire outer peripheral surface of the outer cylindrical body 12. Thus, the tread element 14 is formed in a cylindrical shape extending in the tire width direction around the central axis O. The tread element 14 covers not only the outer peripheral surface of the outer cylindrical body 12 but also the tire radially outer end of the side surface of the outer cylindrical body 12 facing the tire width direction with the side portions 14s of the tread element 14 (see FIG. 5 , etc.). In this embodiment, the elastic modulus of the material forming the tread element 14 is lower than the elastic modulus of the material forming other portions of the non-pneumatic tire 1. The tread element 14 is formed, for example, from natural rubber and / or vulcanized rubber obtained by vulcanizing a rubber composition, a thermoplastic material, or the like. From the viewpoint of wear resistance, it is preferable to form the tread element 14 from vulcanized rubber. Examples of the thermoplastic material include a thermoplastic elastomer and a thermoplastic resin. Examples of the thermoplastic elastomer include amide thermoplastic elastomer (TPA), ester thermoplastic elastomer (TPC), olefin thermoplastic elastomer (TPO), styrene thermoplastic elastomer (TPS), urethane thermoplastic elastomer (TPU), crosslinked thermoplastic rubber (TPV), and other thermoplastic elastomers (TPZ), which are specified in JIS K 6418. Examples of the thermoplastic resin include urethane resin, olefin resin, vinyl chloride resin, and polyamide resin.

[0021] In this embodiment, the outer peripheral surface 14f of the tread element 14 (hereinafter also referred to as the "tread outer peripheral surface 14f") has a curved shape that is convex outward in the tire radial direction in a cross-sectional view in the tire width direction, as shown in Figures 4 and 5. The tread outer peripheral surface 14f becomes the contact surface of the tread element 14. The shape of the tread outer peripheral surface 14f will be described in more detail below, mainly with reference to Figure 5.

[0022] As mentioned above, Fig. 4 is a cross-sectional view taken along line A-A in Fig. 1, i.e., a cross-sectional view in the tire width direction of the non-pneumatic tire 1 in Fig. 1, and Fig. 5 is an enlarged cross-sectional view taken along line B-B in Fig. 4. In this specification, the term "cross-sectional view in the tire width direction (as viewed)" more specifically refers to a cross-sectional view (as viewed) along both the tire width direction and the tire radial direction. In this embodiment, as mentioned above, the inner cylindrical body 11, the outer cylindrical body 12, and the connecting member 13 are integrally formed. Therefore, in the cross-section taken along line A-A in Fig. 1, the boundary line between the outer cylindrical body 12 and the portion 13c of the connecting member 13 connected to the outer cylindrical body 12 does not appear. Therefore, in Figs. 4 and 5, specific parts are indicated by the reference symbols "12, 13c."

[0023] In this embodiment, as described above, the curve on the tread outer peripheral surface 14f (hereinafter also referred to as the "tread outer peripheral surface curve"), which is shaped as a curve that is convex outward in the tire radial direction in a cross section in the tire width direction, is a series of multiple arcs having different radii of curvature. That is, in this embodiment, as shown in Fig. 5, the tread outer peripheral surface curve is a series of multiple (three in the illustrated example) arcs AC1, AC2, and AC3 having different radii of curvature. More specifically, in this embodiment, the tread outer peripheral surface curved line presents an arc AC1 (hereinafter also referred to as the "center arc AC1") with a single radius of curvature R1 in a center region AR1 including the tire widthwise center CL of the tread outer peripheral surface 14f, an arc AC3 (hereinafter also referred to as the "shoulder arc AC3") with a single radius of curvature R3 in shoulder regions AR3 located on the outermost sides in the tire width direction including the tire widthwise outer ends (hereinafter also referred to as the "tread edges") TE of the tread outer peripheral surface 14f, and an arc AC2 (hereinafter also referred to as the "intermediate arc AC2") with a single radius of curvature R2 in an intermediate region AR2 located between the center region AR1 and the shoulder regions AR3 of the tread outer peripheral surface 14f, and these arcs AC1, AC2, and AC3 are continuously connected (however, R1 ≠ R2, R1 ≠ R3, and R2 ≠ R3). In the illustrated example, the center arc AC1, the intermediate arc AC2, and the shoulder arc AC3 are smoothly connected to one another. The centers of curvature of all of these arcs are located radially inward of the tread outer peripheral surface 14f. In this specification, the term "shoulder portion" does not necessarily refer to the same area as the shoulder region AR3, but refers to the entire area near the tread edge TE. In this specification, the term "center portion" does not necessarily refer to the same area as the center region AR1, but refers to the entire area located closer to the center CL in the tire width direction than the shoulder portion. In this specification, the portion of the tread outer peripheral surface 14f formed by a single arc is referred to as a "region," such as a "center region."

[0024] In this embodiment, as shown in Figures 3 to 5, the tread element 14 may have one or more grooves 14g (in this example, two circumferential grooves extending linearly along the tire circumferential direction) in the center region AR1 of the tread outer peripheral surface 14f. However, the tread element 14 may not have grooves, or may have grooves in other regions of the tread outer peripheral surface 14f instead of or in addition to the center region AR1, and may further have grooves at boundary positions between the above-mentioned regions on the tread outer peripheral surface 14f (in other words, positions of connecting points of the arcs described below). When grooves are present on the tread outer peripheral surface 14f, an extrapolated line of the groove on the tread outer peripheral surface 14f (a line smoothly connecting both opening ends of the groove to the tread outer peripheral surface 14f) is considered to be part of the tread outer peripheral surface curve in a cross-sectional view in the tire width direction.

[0025] 4 and 5, the tread element 14 and therefore the tread outer peripheral surface 14f are formed symmetrically on both sides in the tire width direction with the tire width direction center CL as the axis of symmetry. However, the tread element 14 and therefore the tread outer peripheral surface 14f may be formed asymmetrically on both sides in the tire width direction.

[0026] In this embodiment, the radii of curvature of the multiple arcs are smaller toward the outer side in the tire width direction on the tread outer peripheral surface 14f. In other words, between adjacent regions on the tread outer peripheral surface 14f, the radii of curvature of the arcs in the region located on the outer side in the tire width direction are smaller than the radii of curvature of the arcs in the region located on the inner side in the tire width direction. More specifically, with reference to FIG. 5 , in this embodiment, the radius of curvature R2 of the arc AC2 in the intermediate region AR2 is smaller than the radius of curvature R1 of the arc AC1 in the center region AR1. Furthermore, the radius of curvature R3 of the arc AC3 in the shoulder region AR3 is smaller than the radius of curvature R2 of the arc AC2 in the intermediate region AR2.

[0027] The non-pneumatic tire of this embodiment configured as described above has the following effects. First, in the non-pneumatic tire 1 of this embodiment, the outer peripheral surface 14f of the tread element 14 has a curved shape that is convex outward in the tire radial direction in a cross-sectional view in the tire width direction. Therefore, the non-pneumatic tire 14 of this embodiment can appropriately follow various road surface conditions and effectively absorb vibrations transmitted from the ground to the axle, just like a normal pneumatic tire.

[0028] Next, in the non-pneumatic tire 14 of this embodiment, the curve that convexly extends outward in the tire radial direction is a series of multiple arcs AC1 to AC3 with different radii of curvature, and the radii of curvature R1 to R3 of the multiple arcs AC1 to AC3 are smaller toward the outermost arcs in the tire width direction on the outer peripheral surface 14f of the tread element 14. Conventional pneumatic tires have flexible sidewalls on the inner side of the tread in the tire radial direction, resulting in a large amount of deformation in the tire radial direction. However, in the non-pneumatic tire 1, the rigidity of the outer cylindrical body 12 located on the inner side of the tread element 14 in the tire radial direction is very high and the amount of deformation is small. Therefore, when the outer peripheral tread surface 14f is formed as a straight line (flat) or an arc with a large radius of curvature in a cross-sectional view in the tire width direction, the ground contact pressure in the shoulder portion becomes extremely high, particularly when a slip angle or camber angle is applied during driving, causing a wandering phenomenon and the like, which deteriorates steering stability and ultimately reduces maneuverability, and is prone to uneven wear in the shoulder portion of the outer peripheral tread surface 14. On the other hand, in this embodiment, the curve on the tread outer peripheral surface 14f is formed from multiple arcs with smaller radii of curvature toward the outer sides in the tire width direction, thereby suppressing deterioration in maneuverability and uneven wear in the shoulder regions due to excessively high ground contact pressure in the shoulder regions. In other words, the non-pneumatic tire 1 of this embodiment can suppress deterioration in maneuverability and uneven wear in the shoulder regions of the tread element 14. Furthermore, if the curve on the tread outer peripheral surface 14f is formed from a single arc with a single radius of curvature, the ground contact pressure in the center region of the tread outer peripheral surface 14f becomes high, making it more likely that uneven wear will occur in the center region. However, in the non-pneumatic tire 1 of this embodiment, the curve is formed from multiple arcs with different radii of curvature, thereby suppressing uneven wear in the center region.

[0029] Hereinafter, with reference mainly to FIG. 5, preferred aspects and their effects of the non-pneumatic tire 1 according to this embodiment will be further described.

[0030] In this embodiment, the radius of curvature R3 of the shoulder arc AC3, which is the arc located at the outermost position in the tire width direction, i.e., the arc in the shoulder region AR3, is preferably 0.3 times or less the radius of curvature R1 of the center arc AC1, which is the arc at the tire width center CL, i.e., the arc in the center region AR1. In this case, excessively high ground contact pressure in the shoulder region can be more effectively prevented, thereby further suppressing deterioration in maneuverability and uneven wear in the shoulder region of the tread element 14. For the same reason, the radius of curvature R3 of the shoulder arc AC3 is more preferably 0.1 times or less, and even more preferably 0.05 times or less, the radius of curvature R1 of the center arc AC1. The radius of curvature R3 can be, for example, 0.01 times or more the radius of curvature R1. In order to properly and smoothly connect the center arc AC1 and the shoulder arc AC3, the radius of curvature R2 of the intermediate arc AC2 is preferably 0.5 to 0.7 times the radius of curvature R1 of the center arc AC1.

[0031] 5, the tire width direction distance D1 from the tire width center CL to the connection point CP1 between the center arc AC1 and the arc adjacent to the center arc AC1 on the tire width direction outer side, i.e., the intermediate arc AC2 in the intermediate region AR2 (i.e., the connection point between the center region AR1 and the intermediate region AR2 on the tread outer peripheral surface 14f) is preferably less than or equal to two-thirds of the tire width direction distance D3 between the tire width center CL and the tire width direction outer edge TE on the tread outer peripheral surface 14f (in this embodiment, this distance is equal to one-half the tread width TW, which is the tire width direction distance between both tread edges TE). In this case, the radius of curvature of the arc forming the tread outer peripheral surface 14f becomes smaller from a position closer to the tire width center CL, thereby more effectively suppressing deterioration of maneuverability and uneven wear in the shoulder portions of the tread element 14. For the same reason, the distance D1 from the tire widthwise center CL to the connection point CP1 between the center arc AC1 and the intermediate arc AC2 is more preferably 3 / 5 or less, and even more preferably 1 / 2 or less, of the tire widthwise distance D3 between the tire widthwise center CL and the tire widthwise outer end TE. The distance D1 can be, for example, 1 / 3 or more of the distance D3. Furthermore, in order to ensure that the shoulder arc AC3 is appropriately connected to the intermediate arc AC2 and to further reduce the radius of curvature of the tread outer peripheral surface 14f from a position close to the tire widthwise center CL, the distance D2 from the tire widthwise center CL to the connection point CP2 between the intermediate arc AC2 and the shoulder arc AC3 is preferably 1 / 2 or more and 3 / 4 or less of the distance D3.

[0032] As described above, in this embodiment, the curve that forms the shape of the tread outer peripheral surface 14f in a cross-sectional view in the tire width direction is a combination of three arcs AC1 to AC3 with different radii of curvature. In this case, it is possible to effectively suppress deterioration in maneuverability and uneven wear in the shoulder portions of the tread element 14 without making the shape of the tread outer peripheral surface 14f too complex. However, the multiple arcs with different radii of curvature that form the curve may be two or four or more arcs. In other words, in this embodiment, an intermediate arc AC2 does not have to be formed between the center arc AC1 and the shoulder arc AC3, and two or more intermediate arcs AC2 with different radii of curvature may be formed between the center arc AC1 and the shoulder arc AC3.

[0033] The foregoing describes exemplary embodiments of the present invention, and various modifications can be made without departing from the scope of the claims.

[0034] The non-pneumatic tire according to the present invention can be mounted on any type of vehicle and can be particularly suitably mounted on, for example, bicycles, motorcycles, automobiles including light vehicles, and handle-type electric wheelchairs.

[0035] 1: Non-pneumatic tire, 11: Inner cylinder body, 12: Outer cylinder body, 13: Connecting member, 13a, 13b, 13c: Portions of connecting member, 14: Tread member, 14f: Outer peripheral surface of tread member (outer peripheral tread surface), 14g: Groove, 14s: Side portion of tread member, 2: Rim, 2a: Bolt through hole, 3: Tire-rim assembly, AC1: Arc (center arc), AC2: Arc (intermediate arc), AC3: Arc (shoulder arc), AR1: Center region, AR2: Intermediate region, AR3: Shoulder region, CD: Tire circumferential direction, CL: Center in tire width direction, CP1, CP2: Connection points, D1, D2, D3: Distance, O: Central axis, R1, R2, R3: Radius of curvature, RD: Tire radial direction, TE: outer edge (tread edge) of the outer peripheral surface of the tread element in the tire width direction, WD: tire width direction

Claims

1. A non-pneumatic tire comprising an inner cylindrical body, an outer cylindrical body surrounding the inner cylindrical body from the outside in the tire radial direction, an elastically deformable connecting member connecting the inner cylindrical body and the outer cylindrical body to each other, and a tread member provided on the outer peripheral surface of the outer cylindrical body, wherein the outer peripheral surface of the tread member has a curved shape that is convex outward in the tire radial direction in a cross section in the tire width direction, the curve is a series of multiple arcs with different radii of curvature, and the radii of curvature of the multiple arcs are smaller the further outward in the tire width direction the arcs are on the outer peripheral surface of the tread member.

2. A non-pneumatic tire according to claim 1, wherein the radius of curvature of the shoulder arc, which is the arc located at the outermost side in the tire width direction, is 0.3 times or less the radius of curvature of the center arc, which is the arc at the center in the tire width direction.

3. A non-pneumatic tire according to claim 1 or 2, wherein the distance in the tire width direction from the center in the tire width direction to a connection point between a center arc, which is the arc at the center in the tire width direction, and an intermediate arc, which is the arc adjacent to the center arc on the outside in the tire width direction, is 2 / 3 or less of the distance in the tire width direction between the center in the tire width direction and the outer edge in the tire width direction on the outer peripheral surface of the tread element.

4. A non-pneumatic tire according to any one of claims 1 to 3, wherein the curve is a series of three circular arcs each having a different radius of curvature.

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