Pneumatic tires and tire / rim assemblies
The tire design with shoulder grooves and convex bead portions addresses the challenge of rolling resistance by minimizing tread rubber deformation and enhancing bead support, resulting in reduced energy loss and improved durability.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- SUMITOMO RUBBER INDUSTRIES LTD
- Filing Date
- 2024-12-26
- Publication Date
- 2026-07-08
AI Technical Summary
Existing pneumatic tires face challenges in reducing rolling resistance, which is exacerbated by the compressive strain and deformation of the tread rubber at the contact edges, leading to increased energy loss and rolling resistance.
The tire design incorporates a pair of shoulder circumferential grooves adjacent to the tread contact edges, a convex bead portion with a rim-fit profile, and a specific configuration of the belt layer to minimize compressive strain and deformation, ensuring a wide contact area with the rim flange, thereby reducing rolling resistance.
The design effectively reduces rolling resistance by allowing the tread rubber to deform flexibly within the grooves and enhances bead portion support, maintaining durability and reducing energy loss.
Smart Images
Figure 2026114782000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a pneumatic tire and a tire - rim assembly.
Background Art
[0002] Patent Document 1 below describes a pneumatic tire provided with a rim protector. In the bead portion of this tire, a first bead surface and a second bead surface are provided. The first bead surface extends radially outward of the tire from the end of an arc surface that continues to the heel side of the bead base surface that seats on the rim base surface of a standard rim. On the other hand, the second bead surface is connected to the first bead surface via a stepped surface, projects axially outward of the tire more than the first bead surface, and extends radially outward of the tire. In this tire, improvement in the durability of the bead portion is aimed at.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In recent years, reduction of rolling resistance has been demanded.
[0005] In view of the above actual situation, the present invention has been devised, and the main object thereof is to provide a pneumatic tire capable of reducing rolling resistance.
Means for Solving the Problems
[0006] The present invention relates to a pneumatic tire comprising: a tread portion; a pair of bead portions, each provided with a bead core; a carcass extending between the pair of bead portions; and a belt layer disposed on the radially outer side of the carcass and inside the tread portion, wherein the tread portion comprises a pair of tread contact ends and a pair of shoulder circumferential grooves adjacent to each of the pair of tread contact ends and extending continuously in the circumferential direction of the tire, and the belt layer has an outermost belt ply disposed on the outermost side in the radial direction of the tire, and each of the axial outer surfaces of the pair of bead portions has a belt layer on the axial outer side of the tire A pneumatic tire having a protruding apex and a convex portion having a rim-fit profile extending in the circumferential direction of the tire, wherein in a tire meridian cross section in an unloaded, normal state with the pneumatic tire mounted on a rim and filled with normal internal pressure, each of the pair of bead portions has a shortest radial distance of 0 to 3 mm between the apex and the rim flange of the rim, and the axial distance between the pair of shoulder circumferential grooves and the tire equator is 70.0% to 98.5% of the axial distance between the outermost end of the outermost belt ply and the tire equator. [Effects of the Invention]
[0007] By adopting the above configuration, the pneumatic tire of the present invention can reduce rolling resistance. [Brief explanation of the drawing]
[0008] [Figure 1] This is a tire meridian cross-sectional view including the tire rotation axis, showing one embodiment of a tire-rim assembly. [Figure 2] Figure 1 is a magnified view of the tire bead and rim. [Figure 3] This is a close-up view of the tread area. [Figure 4] This is a partial cross-sectional view showing an example of a tire under load. [Modes for carrying out the invention]
[0009] Embodiments of the present invention will be described below with reference to the drawings. It should be understood that the drawings contain exaggerations and representations that differ from the actual dimensional ratios of the structures in order to aid in understanding the content of the invention. Furthermore, the same or common elements are denoted by the same reference numerals throughout each embodiment, and redundant explanations are omitted. Moreover, the specific configurations shown in the embodiments and drawings are for the purpose of understanding the content of the present invention, and the present invention is not limited to the specific configurations shown in the drawings.
[0010] [Tire and Rim Assembly] Figure 1 is a meridional cross-sectional view of a tire including a tire rotation axis (not shown), illustrating one embodiment of the tire-rim assembly (hereinafter sometimes referred to as "assembly") 1. Figure 1 illustrates the meridional cross-sectional view of a tire in a normal state, which will be described later. Figure 2 is a partially enlarged view of the bead portion 14 and rim 3 of the tire 2 in Figure 1. In Figure 2, the tire 2 and rim 3 are shown separately for convenience. Figure 3 is a partially enlarged view of the tread portion 12.
[0011] As shown in Figure 1, the assembly 1 consists of a pneumatic tire (hereinafter sometimes referred to as "tire") 2 and a rim 3 on which the tire 2 is mounted. For example, the tire 2 may be a passenger car tire. The tire 2 may also be a motorcycle tire or a heavy-duty tire.
[0012] [rim] As shown in Figures 1 and 2, the rim 3 is composed of a pair of rim bases 15, 15 and a pair of rim flanges 16, 16. Various types of rims can be used for this rim 3, but the standard rim 3A is preferred.
[0013] A "regular rim" is the rim specified for each tire in the standards system that includes the standard on which the tire is based. Therefore, a regular rim is, for example, a "standard rim" for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO.
[0014] As shown in Fig. 2, the pair of rim bases 15, 15 are for receiving the bottom surfaces 14b, 14b of the pair of bead portions 14, 14 of the tire 2, respectively. On the other hand, the pair of rim flanges 16, 16 are connected to the outer ends in the tire axial direction of the respective rim bases 15, 15 and extend radially outward in the tire radius direction.
[0015] The pair of rim flanges 16, 16 are respectively provided with inner surfaces 16s, 16s facing the inner side in the tire axial direction. By bringing the outer surfaces 14s, 14s in the tire axial direction of the pair of bead portions 14, 14 of the tire 2 into contact with these inner surfaces 16s, 16s respectively, the pair of bead portions 14, 14 can be supported. These inner surfaces 16s, 16s are formed in an arc shape that protrudes toward the inner side in the tire axial direction.
[0016] [Pneumatic Tire] As shown in Fig. 1, the tire 2 of the present embodiment includes a tread portion 12, a pair of sidewall portions 13, 13, a pair of bead portions 14, 14, a carcass 6, and a belt layer 7.
[0017] [Tread Portion] The tread portion 12 is provided with a pair of tread grounding ends 12t, 12t and a pair of shoulder circumferential grooves 18, 18. Further, the tread portion 12 includes a cap rubber 21 that constitutes the grounding surface 12s. A base rubber 22 may be provided inside the cap rubber 21 in the tire radius direction. In the present embodiment, the tread rubber 23 is constituted by the cap rubber 21 and the base rubber 22.
[0018] The pair of tread grounding ends 12t, 12t correspond to the ends of the grounding surface 12s when 70% of the normal load is applied to the tire 2 in the normal state and the tread portion 12 is grounded on a plane at a camber angle of 0°.
[0019] The "normal state" refers to a no-load state where the tire 2 is mounted on the rim 3 (in this example, the normal rim 3A) and filled with the normal internal pressure. In this specification, unless otherwise specified, the dimensions and the like of each part of the assembly 1 are indicated by the values measured in the normal state. Note that the dimensions and the like are allowed to have normal dimensional errors (tolerances) that are inevitable in manufacturing.
[0020] The "normal internal pressure" is the air pressure defined for each tire in a standard system including the standards based on the tire 2. Therefore, the normal internal pressure is, for example, the "maximum air pressure" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.
[0021] The "normal load" is the load defined for each tire in a standard system including the standards based on the tire 2. Therefore, the normal load is, for example, the "maximum load capacity" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "LOAD CAPACITY" in the case of ETRTO.
[0022] [Shoulder circumferential groove] The pair of shoulder circumferential grooves 18, 18 are respectively adjacent to the pair of tread grounding ends 12t, 12t and extend continuously in the tire circumferential direction. The pair of shoulder circumferential grooves 18, 18 of the present embodiment extend linearly along the tire circumferential direction, but are not limited to such a mode. The pair of shoulder circumferential grooves 18, 18 may extend, for example, in a wavy or zigzag shape.
[0023] Generally, the radius of curvature of the ground contact surface 12s of the tread portion 12 is relatively small on the side of the pair of tread grounding ends 12t, 12t. FIG. 4 is a cross-sectional view showing an example of the tire 2 when a load is applied.
[0024] As shown in Figure 4, when the contact surface 12s of the tire 2 is in contact with the road surface (flat surface) and a load is applied, the deformed tread rubber 23 exhibits increased compressive strain in the tire axial direction at the 12t side (the side with the smaller radius of curvature) of the pair of tread contact edges 12t. Such compressive strain tends to be particularly large in the cap rubber 21 on the contact surface 12s side of the tread rubber 23, increasing rolling resistance.
[0025] As shown in Figures 1 and 3, a pair of shoulder circumferential grooves 18, 18 are provided adjacent to a pair of tread contact edges 12t, 12t, respectively. These pairs of shoulder circumferential grooves 18, 18 allow the tread rubber 23 to deform flexibly so that the groove widths W1, W1 (shown in Figure 3) of the pair of shoulder circumferential grooves 18, 18 become smaller when a load is applied to the tire 2 (assembly 1) as shown in Figure 4. As a result, the tread rubber 23 (cap rubber 21) expands (moves into) the groove space of the pair of shoulder circumferential grooves 18, 18, reducing (absorbing) the compressive strain of the tread rubber 23 (cap rubber 21) that is large on the tread contact edge 12t, 12t side. Therefore, the rolling resistance of the tire 2 (assembly 1) is reduced.
[0026] As shown in Figure 3, the groove widths W1, W1 of the pair of shoulder circumferential grooves 18, 18 are preferably set to 1 to 5 mm. By setting each groove width W1, W1 to 1 mm or more, the groove space (groove volume) of the pair of shoulder circumferential grooves 18, 18 is secured. As a result, when a load is applied to the tire 2 (assembly 1) shown in Figure 4, the tread rubber 23 (cap rubber 21) can spread (enter) sufficiently into the groove space of the pair of shoulder circumferential grooves 18, 18, and rolling resistance can be effectively reduced. From this viewpoint, the groove widths W1, W1 are preferably 1.4 mm or more, and more preferably 1.8 mm or more. On the other hand, by setting each groove width W1, W1 to 5 mm or less, the increase in air column resonance noise of the pair of shoulder circumferential grooves 18, 18 during tire operation can be suppressed, and the deterioration of external noise can be prevented. From this perspective, each groove width W1, W1 is preferably 4 mm or less, and more preferably 3 mm or less, in any combination of the lower limits mentioned above. In this embodiment, the most preferred groove width W1, W1 is 2 mm, but is not particularly limited.
[0027] As shown in Figure 3, the groove depths D1, D1 of the pair of shoulder circumferential grooves 18, 18 are preferably set to 3 to 7 mm. By setting each groove depth D1, D1 to 3 mm or more, the groove space (groove volume) of the pair of shoulder circumferential grooves 18, 18 is secured. As a result, when a load is applied to the tire 2 (assembly 1) shown in Figure 4, the tread rubber 23 (cap rubber 21) can spread (enter) sufficiently into the groove space of the pair of shoulder circumferential grooves 18, 18, and rolling resistance can be effectively reduced. From this viewpoint, each groove depth D1, D1 is preferably 3.4 mm or more, and more preferably 3.8 mm or more. On the other hand, by setting each groove depth D1, D1 to 7 mm or less, it is possible to suppress the reduction in the rubber thickness of the tread rubber 23 (cap rubber 21) at the bottom of the grooves of the pair of shoulder circumferential grooves 18, 18. This suppresses the decrease in the amount of oil used to prevent deterioration in the tread rubber 23, thereby effectively preventing the progression of cracks due to deterioration of the tread rubber 23. From this viewpoint, each groove depth D1, D1 is preferably 6 mm or less, and more preferably 5 mm or less, in any combination of the lower limits mentioned above. In this embodiment, the most preferred groove depth D1, D1 is 4 mm, but the embodiment is not limited to this.
[0028] [Center circumferential groove, middle circumferential groove] As shown in Figure 1, the tread portion 12 may be provided with a pair of center circumferential grooves 19, 19 and a pair of middle circumferential grooves 20, 20 between a pair of shoulder circumferential grooves 18, 18. These pair of center circumferential grooves 19, 19 and the pair of middle circumferential grooves 20, 20 improve wet grip. As shown in Figure 3, the groove widths W2a, W2b and groove depths D2a, D2b of the pair of center circumferential grooves 19, 19 and the pair of middle circumferential grooves 20, 20 can be set as appropriate. In this embodiment, the groove widths W2a, W2b are set, for example, to 2.0% to 8.0% of the tread contact width TW shown in Figure 1. The groove depths D2a, D2b are set, for example, to 4.0 to 10.0 mm. The tread contact width TW is defined as the distance in the tire axial direction between a pair of tread contact edges 12t, 12t.
[0029] [Bead section] As shown in Figure 1, each of the pair of bead sections 14, 14 is provided with bead cores 5, 5. Each bead core 5, 5 is made of, for example, a steel bead wire (not shown) wound in multiple rows and layers. In addition, each of the bead cores 5, 5 is provided with a bead apex 8, 8 made of hard rubber on its radially outer side. As shown in Figures 1 and 2, each of the pair of bead sections 14, 14 is provided with clinch rubber 24, 24 that constitute their respective outer surfaces 14s, 14s.
[0030] In this embodiment, each of the outer surfaces 14s, 14s of the pair of bead portions 14, 14 (clinch rubber 24, 24) in the tire axial direction has a protrusion 25, 25 formed on them.
[0031] As shown in Figure 2, each convex portion 25, 25 has a top portion 26, 26 that protrudes outward in the tire axial direction and extends in the tire circumferential direction. Each of the outer surfaces 27, 27 of the convex portions 25, 25 in this embodiment includes an inner arcuate surface (hereinafter sometimes referred to as the "rim fit profile") 27i and an outer arcuate surface 27o.
[0032] The rim fit profile 27i extends radially inward from the top portion 26. In this embodiment, the outer end of the rim fit profile 27i in the tire axial direction is configured as the top portion 26.
[0033] In this embodiment, the rim fit profile 27i is formed in an arc shape that is convex toward the inward direction in the tire axial direction. As a result, the rim fit profile 27i is shaped to conform to the inner surface 16s of the rim flange 16 in the tire axial direction, and a contact area between the rim flange 16 and the convex portion 25 (rim fit profile 27i) can be secured. Therefore, as shown in Figure 4, when a load is applied to the tire 2 (assembly 1), the pair of bead portions 14, 14 are firmly supported by the rim flanges 16, 16, and bending deformation of the bead portions 14, 14 can be suppressed. As a result, the heat generation (energy loss) associated with the deformation of the bead portions 14, 14 (clinch rubber 24, 24) is reduced, and consequently, the rolling resistance of the tire 2 (assembly 1) is reduced.
[0034] As shown in Figure 1, in the normal state of the tire meridian cross section of tire 2, each of the pair of bead portions 14, 14 has a minimum radial distance E1, E1 between the tops 26, 26 of the convex portions 25, 25 and the rim flanges 16, 16 of the tire limited to 0 to 3 mm.
[0035] By setting each shortest distance E1, E1 to 3 mm or less, a wide contact area with the rim flange 16 can be secured over a wide area of the outer surface 27 (rim fit profile 27i) of the protrusion 25 shown in Figure 2. As a result, when a load is applied to the tire 2 (assembly 1) shown in Figure 4, the bead portions 14, 14 are firmly supported by the rim flanges 16, 16, and bending deformation of the bead portions 14, 14 (clinch rubber 24, 24) can be suppressed. Therefore, the heat generation (energy loss) associated with the deformation of the bead portions 14, 14 (clinch rubber 24, 24) is reduced, and consequently, the rolling resistance of the tire 2 (assembly 1) is reduced. In order to effectively exert this effect, each shortest distance E1, E1 is preferably 2 mm or less, more preferably 1 mm or less, and most preferably 0 mm.
[0036] As shown in Figure 2, the outer arc surface 27o extends radially outward from the apex 26. In this embodiment, the outer arc surface 27o is formed in an arc shape that is convex toward the inward direction in the tire axial direction, but it is not particularly limited.
[0037] In this embodiment, the outer arc surface 27o may have a larger radius of curvature than the rim fit profile 27i. This outer arc surface 27o ensures the rubber volume (rigidity) of the clinch rubber 24 radially outward from the top 26 of the tire. As a result, deformation of the bead portions 14, 14 (clinch rubber 24, 24) can be suppressed when a load is applied to the tire 2 (assembly 1) shown in Figure 4. Therefore, the heat generated (energy loss) associated with the deformation of the bead portions 14, 14 (clinch rubber 24, 24) is reduced, and consequently, rolling resistance is reduced.
[0038] [Carcass] As shown in Figure 1, the carcass 6 extends between a pair of bead portions 14, 14. The carcass 6 is composed of at least one (one in this example) carcass ply 6A. The carcass ply 6A includes, for example, a main body portion 6a and a pair of folded portions 6b, 6b. The main body portion 6a extends, for example, between the pair of bead portions 14, 14. Each folded portion 6b, 6b is connected to the main body portion 6a and folded back from the inside to the outside in the tire axial direction around the bead cores 5, 5.
[0039] The carcass ply 6A includes a plurality of carcass cords (not shown) and a topping rubber covering them (not shown). The carcass cords may be organic fiber cords such as aramid or rayon. Preferably, the carcass cords are arranged at an angle of 70 to 90° with respect to the circumferential direction of the tire.
[0040] [Belt layer] The belt layer 7 is located on the radially outer side of the carcass 6 and inside the tread portion 12. This belt layer 7 has an outermost belt ply 7A located on the outermost side in the radial direction of the tire. Furthermore, the belt layer 7 of this embodiment has one inner belt ply 7B located radially inward of the outermost belt ply 7A, but this is not particularly limited and may be omitted or may have two or more depending on the performance required of the tire 2.
[0041] The outermost belt ply 7A and the inner belt ply 7B are, for example, made up of belt cords (not shown) arranged at an angle of 10 to 35° with respect to the circumferential direction of the tire, which are superimposed in a direction that intersects with each other.
[0042] The outermost belt ply 7A's outer ends 7At, 7At in the tire axial direction may be misaligned with the inner belt ply 7Bt, 7Bt in the tire axial direction. This suppresses the concentration of strain at the outer end 7At of the outermost belt ply 7A (belt layer 7) due to the difference in rigidity, when a load is applied to the tire 2 as shown in Figure 4, thereby maintaining the durability of the belt layer 7.
[0043] The outermost belt ply 7A's outer ends 7At, 7At may be positioned further inward in the tire axial direction than the outermost belt ply 7Bt, 7Bt of the inner belt ply 7B. This can suppress the increase in axial compressive strain in the tread rubber 23 (cap rubber 21) adjacent to the outermost belt ply 7A when a load is applied to the tire 2. In this case, as shown in Figure 1, the tire axial width W3 of the outermost belt ply 7A may be set to, for example, 90% to 98% of the tread contact width TW. On the other hand, the tire axial width W4 of the inner belt ply 7B may be set to, for example, 101% to 105% of the tread contact width TW.
[0044] As shown in Figure 3, the axial distance F1 between a pair of shoulder circumferential grooves 18, 18 and the tire equator C (hereinafter sometimes referred to as the "shoulder circumferential groove distance") is limited to 70.0% to 98.5% of the axial distance F2 between the outermost end 7At of the outermost belt ply 7A and the tire equator C (hereinafter sometimes referred to as the "outermost belt ply distance"). Here, the distance F1 of the shoulder circumferential groove 18 is determined at the intersection 30 of the groove centerline 28 of the shoulder circumferential groove 18 and the imaginary line of the contact surface 12s. Note that if the shoulder circumferential groove 18 extends in a wavy or zigzag pattern, the distance F1 of the shoulder circumferential groove 18 can be determined as the average axial distance between the shoulder circumferential groove 18 and the tire equator C.
[0045] By setting the distance F1 of the shoulder circumferential groove 18 to 70.0% or more of the distance F2 of the outermost belt ply 7A, a pair of shoulder circumferential grooves 18, 18 can be provided on the tread contact edge 12t, 12t side. As described above, on the tread contact edge 12t, 12t side, the compressive strain of the tread rubber 23 increases when a load is applied to the tire 2 as shown in Figure 4. By deforming the tread rubber 23 (cap rubber 21) so that the groove width W1, W1 (shown in Figure 3) of the pair of shoulder circumferential grooves 18, 18 provided on the tread contact edge 12t, 12t side becomes smaller, the rolling resistance of the tire 2 (assembly 1) can be reduced. In order to effectively exert this effect, the distance F1 of the shoulder circumferential groove 18 is preferably 85% or more of the distance F2 of the outermost belt ply 7A, and more preferably 90% or more of the distance F2 of the outermost belt ply 7A.
[0046] On the other hand, by setting the distance F1 of the shoulder circumferential grooves 18 to 98.5% or less of the distance F2 of the outermost belt ply 7A, the pair of shoulder circumferential grooves 18, 18 can be positioned inward in the tire axial direction from the outer ends 7At, 7At of the outermost belt ply 7A. As a result, when a load is applied to the tire 2 as shown in Figure 4, the concentration of strain at the outer ends 7At, 7At of the outermost belt ply 7A due to the bending deformation of the tread portion 12 starting from the shoulder circumferential grooves 18, 18 can be suppressed. Therefore, delamination between the outer ends 7At, 7At of the outermost belt ply 7A and the outer ends 7Bt, 7Bt of the inner belt ply 7B can be suppressed, and the durability of the belt layer 7 can be maintained. In order to effectively exert this effect, the distance F1 of the shoulder circumferential grooves 18 is preferably 96% or less of the distance F2 of the outermost belt ply 7A, and more preferably 95% or less of the distance F2 of the outermost belt ply 7A, in any combination of the lower limits mentioned above. In this embodiment, the most preferred distance F1 of the shoulder circumferential groove 18 is 94% of the distance F2 of the outermost belt ply 7A.
[0047] Thus, in the tire 2 (assembly 1) of this embodiment, by limiting the shortest distance E1, E1 shown in Figure 1 to 0-3 mm, a protrusion 25 having a rim fit profile 27i along the rim flange 16 can be formed. This suppresses bending deformation of the bead portions 14, 14 (clinch rubber 24, 24), and rolling resistance can be reduced. However, if only a protrusion 25 having a rim fit profile 27i is formed, the bending deformation of the bead portions 14, 14 (clinch rubber 24, 24) is suppressed, and when a load is applied to the tire 2 as shown in Figure 4, the compressive strain at the tread contact end 12t, 12t of the tread rubber 23 becomes large, and the rolling resistance may not be sufficiently reduced. In this embodiment, by limiting the distance F1 of the shoulder circumferential groove 18 shown in Figure 3 to 70.0% or more of the distance F2 of the outermost belt ply 7A, the compressive strain of the tread portion 12 (tread rubber 23) is reduced, and the rolling resistance of the tire 2 can be effectively reduced. Therefore, the rolling resistance of the tire 2 (assembly 1) of this embodiment can be effectively reduced by the synergistic effect of limiting both the shortest distance E1, E1 and the distance F1 of the shoulder circumferential groove 18 and the distance F2 of the outermost belt ply 7A to the above range. In addition, the durability of the belt layer 7 can be maintained by limiting the distance F1 of the shoulder circumferential groove 18 to 98.5% or less of the distance F2 of the outermost belt ply 7A.
[0048] In this embodiment, the groove widths W1, W1 of the pair of shoulder circumferential grooves 18, 18 are set to 1 to 5 mm, and the groove depths D1, D1 are set to 3 to 7 mm. The synergistic effect of limiting these groove widths W1, W1 and groove depths D1, D1, and the distance F1 of the shoulder circumferential grooves 18 and the distance F2 of the outermost belt ply 7A to the above ranges can more effectively reduce the rolling resistance of the tire 2 (assembly 1).
[0049] As shown in Figure 2, the distance in the tire axial direction (hereinafter sometimes referred to as "overhang height") H between the top 26 of the protrusion 25 and the tire radial line RL that defines the rim width Rw of the rim 3 (see, for example, JATMA) is preferably set to 7 to 12 mm. By setting the overhang height H to 7 mm or more, the contact area between the protrusion 25 (rim fit profile 27i) and the rim flange 16 can be further increased due to the synergistic effect of limiting the shortest distance E1 shown in Figure 1 to 0 to 3 mm. As a result, when a load is applied to the tire 2 as shown in Figure 4, the bead portion 14 is firmly supported by the rim flange 16, and bending deformation of the bead portion 14 is suppressed, thereby effectively reducing the rolling resistance of the tire 2 (assembly 1). In order to effectively exert this effect, the overhang height H is preferably 8 mm or more, and more preferably 9 mm or more.
[0050] On the other hand, by setting the protrusion height H to 12 mm or less, the rubber volume of the protrusion 25 (clinch rubber 24) is prevented from becoming unnecessarily large. This prevents an increase in energy loss and can reduce the rolling resistance of the tire 2 (assembly 1). In order to effectively exert this effect, the protrusion height H is preferably 11 mm or less, and more preferably 10 mm or less, in any combination of the lower limits mentioned above. In this embodiment, the most preferred protrusion height H is 9.5 mm.
[0051] As shown in Figure 1, the loss tangent tanδ of the cap rubber 21 is preferably set to 0.15 to 0.45. In this specification, the loss tangent tanδ is a value measured using a GABO dynamic viscoelasticity measuring device (Iplexer series) under the following conditions in accordance with the provisions of JIS-K6394. Furthermore, a cap rubber 21 having a loss tangent tanδ within the above range can be manufactured by appropriately adjusting and combining known materials. Initial strain: 5% Dynamic strain amplitude: ±1% Frequency: 10Hz Deformation mode: Stretch Measurement temperature: 30℃
[0052] By setting the loss tangent tanδ to 0.45 or less, the compression strain associated with the deformation of the cap rubber 21 when a load is applied to the tire 2 (assembly 1) is suppressed, and rolling resistance can be reduced. To effectively exert this effect, the loss tangent tanδ is preferably 0.40 or less, and more preferably 0.35 or less. On the other hand, by setting the loss tangent tanδ to 0.15 or more, steering stability can be maintained. From this viewpoint, the loss tangent tanδ is preferably 0.17 or more, and more preferably 0.19 or more, in any combination of the lower limits mentioned above. The most preferred loss tangent tanδ is 0.20.
[0053] Although particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be implemented in various modified forms. [Examples]
[0054] [Example A] Pneumatic tires having the basic structure shown in Figure 1 were prototyped based on the specifications in Table 1 (Examples 1 to 3). For comparison, comparative examples 1 and 3, which lacked a protrusion with a rim-fit profile, and comparative example 2, which lacked a shoulder circumferential groove, were prototyped. Furthermore, comparative example 4, in which the shortest distance E1 between the top and the rim flange was greater than 3 mm, and comparative example 5, in which the shoulder circumferential groove distance F1 exceeded 98.5% of the outermost belt ply distance F2, were prototyped. The rolling resistance performance and belt ply durability of these prototyped tires were then tested. The common specifications and test methods are as follows. Tire size: 235 / 60R18 Rim size: 18×7J Internal pressure: 250kPa Protrusion height H: 9.5mm Shoulder circumferential grooves: Groove width W1: 2mm Groove depth D1: 4mm Loss tangent tanδ of the cap rubber: 0.2 Distance of the outermost belt ply: F2: 85mm
[0055] <Rolling resistance performance> In accordance with ECE R117-02 (ECE Regulation No. 117 Revision 2), prototype tires were run on a simulated road surface in an indoor drum testing machine, and their rolling resistance values were measured. The evaluation was expressed as an index with the reciprocal of the rolling resistance value of Comparative Example 1 set to 100. The results showed that a higher numerical value indicates reduced rolling resistance and superior rolling resistance performance. Vertical load: 5.94kN Speed: 80km / h
[0056] <Durability of the belt layer> The prototype tires were driven on a simulated road surface in an indoor drum testing machine, and the distance traveled until a failure occurred in the belt layer was recorded. The evaluation was expressed as an index with the distance traveled in Comparative Example 1 set to 100. The results showed that a higher numerical value indicates better durability of the belt layer. Vertical load: 5.94kN Speed: 80km / h The test results are shown in Table 1.
[0057] [Table 1]
[0058] The test results showed that Examples 1-3 were able to reduce rolling resistance while maintaining the durability of the belt layer, compared to Comparative Examples 1-5.
[0059] [Example B] A pneumatic tire having the basic structure shown in Figure 1 was prototyped based on the specifications in Table 2 (Examples 1 and 4-7). The rolling resistance performance and belt ply durability of these prototyped tires were then tested. The common specifications are as described in Example A, except for the specifications in Table 2 and the specifications described below. The test method is as described in Example A. Convex part (rim fit profile): Yes Shoulder circumferential groove: Yes The shortest distance between the top and the rim flange is E1: 0mm Shoulder circumferential groove distance F1 / Outermost belt ply distance F2: 94.0% The test results are shown in Table 2.
[0060] [Table 2]
[0061] The test results showed that Examples 1 and 4-7 were able to reduce rolling resistance while maintaining the durability of the belt layer compared to Comparative Examples 1-5 in Table 1. Furthermore, compared to Examples 6 and 7, in which the groove width W1 and groove depth D1 of the shoulder circumferential grooves were smaller than the preferred range, Example 1 allowed the tread rubber (cap rubber) to expand within the groove space of the shoulder circumferential grooves when a load was applied to the tire. As a result, rolling resistance was reduced.
[0062] [Note] The present invention includes the following embodiments.
[0063] [Invention 1] It is a pneumatic tire, The tread section and, A pair of bead sections, each equipped with a bead core, A carcass extending between the pair of bead portions, The carcass includes a belt layer disposed on the radially outer side of the tire and inside the tread portion, The tread portion includes a pair of tread contact ends and a pair of shoulder circumferential grooves adjacent to each of the pair of tread contact ends and extending continuously in the circumferential direction of the tire. The belt layer has an outermost belt ply that is located on the outermost side in the radial direction of the tire, Each of the pair of bead portions has a convex portion formed on its outer surface in the tire axial direction, which has a top that protrudes outward in the tire axial direction and has a rim-fit profile that extends in the tire circumferential direction. In the meridian cross-section of the tire in an unloaded, normal state, with the aforementioned pneumatic tire mounted on the rim and filled with the normal internal pressure, Each of the pair of bead portions has a minimum distance of 0 to 3 mm in the radial direction between the top and the rim flange of the rim. The distance in the tire axial direction between the pair of shoulder circumferential grooves and the tire equator is 70.0% to 98.5% of the distance in the tire axial direction between the outermost end of the outermost belt ply and the tire equator. Pneumatic tires. [2nd Invention] The pneumatic tire according to Invention 1, wherein the distance in the tire axial direction between the top portion and the tire radial line defining the rim width of the rim is 7 to 12 mm. [Invention 3] The pneumatic tire according to invention 1 or 2, wherein the groove width of the pair of shoulder circumferential grooves is 1 to 5 mm. [4th Invention] The pneumatic tire according to any one of inventions 1 to 3, wherein the groove depth of the pair of shoulder circumferential grooves is 3 to 7 mm. [5th Invention] The tread portion includes a cap rubber that forms the contact surface. The pneumatic tire according to any one of inventions 1 to 4, wherein the loss tangent tanδ of the cap rubber is 0.15 to 0.45. [Invention 6] A pneumatic tire according to any one of inventions 1 to 5, and a rim on which the pneumatic tire is mounted, Tire and rim assembly. [Explanation of Symbols]
[0064] 2. Pneumatic tires 3 rims 7 Belt layer 7A Outermost belt ply 12 Tread section 12t tread contact point 14 Bead section 16 Rim flange 18 Shoulder circumferential grooves 25 Convex part 27i Rim Fit Profile 26 Top C Tire Equator
Claims
1. It is a pneumatic tire, The tread section and, A pair of bead sections, each equipped with a bead core, A carcass extending between the pair of bead portions, The carcass includes a belt layer disposed on the radially outer side of the tire and inside the tread portion, The tread portion includes a pair of tread contact ends and a pair of shoulder circumferential grooves adjacent to each of the pair of tread contact ends and extending continuously in the circumferential direction of the tire. The belt layer has an outermost belt ply that is located on the outermost side in the radial direction of the tire, Each of the pair of bead portions has a convex portion formed on its outer surface in the tire axial direction, which has a top that protrudes outward in the tire axial direction and has a rim-fit profile that extends in the tire circumferential direction. In the meridian cross-section of the tire in an unloaded, normal state, with the aforementioned pneumatic tire mounted on the rim and filled with the normal internal pressure, Each of the pair of bead portions has a minimum distance of 0 to 3 mm in the radial direction between the top and the rim flange of the rim. The distance in the tire axial direction between the pair of shoulder circumferential grooves and the tire equator is 70.0% to 98.5% of the distance in the tire axial direction between the outermost end of the outermost belt ply and the tire equator. Pneumatic tires.
2. The pneumatic tire according to claim 1, wherein the distance in the tire axial direction between the top portion and the tire radial line defining the rim width of the rim is 7 to 12 mm.
3. The pneumatic tire according to claim 1, wherein the groove width of the pair of shoulder circumferential grooves is 1 to 5 mm.
4. The pneumatic tire according to claim 1, wherein the groove depth of the pair of shoulder circumferential grooves is 3 to 7 mm.
5. The tread portion includes a cap rubber that forms the contact surface. The pneumatic tire according to claim 1, wherein the loss tangent tanδ of the cap rubber is 0.15 to 0.
45.
6. A pneumatic tire according to any one of claims 1 to 5, and a rim on which the pneumatic tire is mounted, Tire and rim assembly.