WO2022208971A1 - ランフラットタイヤ - Google Patents
ランフラットタイヤ Download PDFInfo
- Publication number
- WO2022208971A1 WO2022208971A1 PCT/JP2021/040884 JP2021040884W WO2022208971A1 WO 2022208971 A1 WO2022208971 A1 WO 2022208971A1 JP 2021040884 W JP2021040884 W JP 2021040884W WO 2022208971 A1 WO2022208971 A1 WO 2022208971A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- tire
- rubber
- run
- side reinforcing
- elastic modulus
- Prior art date
Links
- 229920001971 elastomer Polymers 0.000 claims abstract description 85
- 239000005060 rubber Substances 0.000 claims abstract description 85
- 239000011324 bead Substances 0.000 claims abstract description 35
- 230000003014 reinforcing effect Effects 0.000 claims description 42
- RRHGJUQNOFWUDK-UHFFFAOYSA-N Isoprene Chemical compound CC(=C)C=C RRHGJUQNOFWUDK-UHFFFAOYSA-N 0.000 claims description 6
- VQTUBCCKSQIDNK-UHFFFAOYSA-N Isobutene Chemical group CC(C)=C VQTUBCCKSQIDNK-UHFFFAOYSA-N 0.000 claims description 3
- 229920001577 copolymer Polymers 0.000 claims description 3
- 238000005259 measurement Methods 0.000 claims description 2
- 230000002787 reinforcement Effects 0.000 abstract description 6
- 230000006866 deterioration Effects 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 229920005549 butyl rubber Polymers 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000005452 bending Methods 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 244000043261 Hevea brasiliensis Species 0.000 description 1
- 239000005062 Polybutadiene Substances 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229920003052 natural elastomer Polymers 0.000 description 1
- 229920001194 natural rubber Polymers 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 229920002857 polybutadiene Polymers 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C17/00—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor
- B60C17/0009—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts
- B60C17/0027—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts comprising portions of different rubbers in a single insert
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C5/00—Inflatable pneumatic tyres or inner tubes
- B60C5/12—Inflatable pneumatic tyres or inner tubes without separate inflatable inserts, e.g. tubeless tyres with transverse section open to the rim
- B60C5/14—Inflatable pneumatic tyres or inner tubes without separate inflatable inserts, e.g. tubeless tyres with transverse section open to the rim with impervious liner or coating on the inner wall of the tyre
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C17/00—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor
- B60C17/0009—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts
- B60C17/0018—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts two or more inserts in each sidewall portion
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C17/00—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor
- B60C17/0009—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts
- B60C17/0036—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts comprising additional reinforcements
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
- B60C9/02—Carcasses
- B60C9/14—Carcasses built-up with sheets, webs, or films of homogeneous material, e.g. synthetics, sheet metal, rubber
- B60C2009/145—Carcasses built-up with sheets, webs, or films of homogeneous material, e.g. synthetics, sheet metal, rubber at the inner side of the carcass structure
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C17/00—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor
- B60C17/0009—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts
- B60C2017/0054—Physical properties or dimensions of the inserts
- B60C2017/0063—Modulus; Hardness; Loss modulus or "tangens delta"
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C17/00—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor
- B60C17/0009—Tyres characterised by means enabling restricted operation in damaged or deflated condition; Accessories therefor comprising sidewall rubber inserts, e.g. crescent shaped inserts
- B60C2017/0054—Physical properties or dimensions of the inserts
- B60C2017/0072—Thickness
Definitions
- the present invention relates to runflat tires.
- an object of the present invention is to provide a runflat tire that suppresses deterioration in ride comfort while ensuring runflat durability.
- the gist and configuration of the present invention are as follows. (1) a tread portion; a pair of sidewall portions continuous on both sides of the tread portion; a bead portion connected to each of the sidewall portions; a side reinforcing rubber having a crescent-shaped cross section disposed on the sidewall; A run-flat tire comprising a carcass that toroidally straddles between the pair of bead portions, A portion of the side reinforcing rubber is a low elastic portion having a lower elastic modulus than the other portions,
- the low-elasticity portion has a tire diameter of 50% or more and 80% or less of the tire cross-sectional height from the bead base line in a standard state in which the run-flat tire is mounted on an applicable rim, filled with a specified internal pressure, and no load is applied.
- the elastic modulus of the low elastic portion is 80% or less of the elastic modulus of the other portion,
- the maximum thickness of the low-elasticity portion measured in the direction of the perpendicular drawn from the carcass to the inner surface of the tire is t1
- the maximum thickness is t1.
- the ratio t1/t2 is 0.2 or more and 3 or less
- the maximum tire width in the reference state is not less than the central value of the maximum tire width specified by the standard and not more than the upper limit,
- the "elastic modulus” is based on the modulus tensile elastic modulus at 25% elongation at 25 ° C. (JIS K 6251: 2017). It refers to the tensile modulus at 25% elongation at °C.
- the term “applicable rim” refers to an industrial standard effective in the region where tires are produced and used, such as JATMA (Japan Automobile Tire Manufacturers Association) JATMA YEAR BOOK in Japan and ETRTO (Japan Automobile Tire Manufacturers Association) in Europe. The European Tire and Rim Technical Organization's STANDARDS MANUAL, TRA's (The Tire and Rim Association, Inc.) YEAR BOOK in the United States, etc.
- Measuring Rim in STANDARDS MANUAL, Design Rim in TRA's YEAR BOOK that is, the above “rim” includes sizes that may be included in the above industrial standards in the future in addition to current sizes.
- the size described the size described as “FUTURE DEVELOPMENTS” in the ETRTO 2013 edition can be mentioned.
- “specified internal pressure” refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel in the applicable size and ply rating described in JATMA, etc., and for sizes not described in the above industrial standards.
- the "specified internal pressure” refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted.
- the "standard” relating to the maximum width of the tire refers to the industrial standard valid for the area where the tire is produced and used.
- the "bead base line” refers to an imaginary line passing through the bead base and parallel to the tire width direction in the above reference state.
- FIG. 1 is a partial sectional view in the tire width direction of a run-flat tire according to one embodiment of the present invention.
- FIG. 1 shows a cross section in the tire width direction of a run-flat tire in the above reference state.
- this run-flat tire (hereinafter also simply referred to as a tire) 10 includes a tread portion 1 made of tread rubber and sidewall portions 2 made of a pair of sidewall rubbers connected to both sides of the tread portion 1. , and a bead portion 3 connected to each sidewall portion 2 .
- each bead portion 3 has a bead core 3a embedded therein. Further, in this example, a bead filler 3b is arranged outside the bead core 3a in the tire radial direction.
- the tire 1 further includes a carcass 4 made up of one or more carcass plies extending between the pair of bead portions 3 in a toroidal manner.
- the carcass ply is made of organic fiber cords in this example.
- the carcass 4 consists of a carcass main body portion 4a engaged with the bead core and a carcass folded portion 4b extending from the carcass main body portion 4a and folded back around the bead core 3a.
- the carcass turn-up portion 4b extends to the inner side in the tire width direction from the belt end and terminates, forming a so-called envelope structure, but the present invention is not limited to this example. It may be positioned radially inward of the tire maximum width position.
- a belt 5 made up of one or more belt layers 5a and 5b (two layers in the illustrated example) is arranged outside the crown portion of the carcass 4 in the tire radial direction.
- the belt cords of the two belt layers extend so as to cross each other between the layers, and the belt cords can extend at an inclination angle of, for example, 30 to 60° with respect to the tire circumferential direction.
- the belt cords are steel cords in this example.
- the maximum tire width is equal to or more than the central value of the maximum tire width defined by the standard and equal to or less than the upper limit value in the above reference state.
- the maximum tire width can be greater than or equal to the center value and less than or equal to the intermediate value, or can be greater than the intermediate value and less than or equal to the upper limit value.
- the maximum tire width position in the reference state is positioned radially outward of a position spaced apart from the bead base line in the radial direction outward by 50% of the tire cross-section height.
- the tire maximum width position in the above reference state is the tire section height outside the bead base line in the tire radial direction from the position spaced apart from the tire radial direction outside by 50% of the tire section height, and from the bead base line to the tire radial direction outside. 60% of or inside in the tire radial direction.
- the maximum width position of the tire in the above-mentioned reference state can also be set to the outer side in the tire radial direction of a position spaced apart from the bead base line in the tire radial direction by 60% of the tire cross-sectional height.
- the carcass line has a shape that substantially follows the profile of the outer surface of the tire.
- the sidewall portion 2 is provided with a side reinforcing rubber 6 having a crescent-shaped cross section.
- the side reinforcing rubbers 6 which contribute to supporting the weight of the vehicle body, can safely travel a certain distance even when the internal pressure of the tire is reduced due to a puncture or the like. to enable.
- the thickness of the side reinforcing rubber 6 in the tire width direction gradually decreases from the vicinity of the tire radial direction center position of the side reinforcing rubber 6 toward the tire radial direction inner side and outer side in the tire width direction cross section, and It has a shape that protrudes outward in the tire width direction.
- part of the side reinforcing rubber 6 is the low elastic portion 6b having a lower elastic modulus than the other portion 6a. More specifically, the elastic modulus of the low elastic portion 6b is 80% or less of the elastic modulus of the other portion 6a, preferably the elastic modulus of the low elastic portion 6b is 50% of the elastic modulus of the other portion 6a. % or less, and more preferably, the elastic modulus of the low elastic portion 6b is 20% or less of the elastic modulus of the other portion 6a.
- the low-elasticity portion 6b is positioned in a tire radial direction region of 50% or more and 80% or less of the tire cross-sectional height from the bead base line in the above reference state.
- the low-elasticity portion 6b (all or part of the low-elasticity portion 6b) is larger than the other portions 6a in a tire radial region of 50% or more and 80% or less of the tire cross-sectional height from the bead base line. It is located on the outer side in the tire width direction.
- only the other portion 6a is positioned at the position in the tire radial direction, which is the position of the maximum tire width (a line parallel to the tire width direction passing through the position of the maximum tire width and the low-elasticity portion 6b). do not intersect).
- the maximum thickness of the low-elasticity portion 6b when measured in the direction of the vertical line drawn down from the carcass 4 to the inner surface of the tire is the maximum thickness t1.
- the ratio t1/t2 is 0.2 or more and 3 or less (more preferably 0.5 or more and 1.5 or less).
- the low-elasticity portion 6b has the maximum thickness measured in the direction of the perpendicular line, but is located near the center along the carcass 4, but the present invention is not limited to this. The effects of the run-flat tire of this embodiment will be described below.
- the present inventors have made extensive studies to solve the above problems, and have focused on the contribution of the side reinforcement rubber to supporting the load during both normal running and run-flat running of the run-flat tire. As a result, it was found that the buttress contributes more to the load support during normal driving than during run-flat driving. I got the knowledge that it is possible.
- the load in this region can be supported during normal running. Since the contribution to the acceleration is relatively large, the elastic modulus of the low-elasticity portion 6b is low, thereby reducing the longitudinal spring coefficient and improving ride comfort. On the other hand, during run-flat running, the contribution of this region to the load support is relatively small, so that deterioration in durability during run-flat running due to the low elastic modulus of the low-elasticity portion 6b can be suppressed.
- the elastic modulus of the low elastic portion 6b is more than 80% of the elastic modulus of the other portion 6a, the effect of improving ride comfort during normal running cannot be sufficiently obtained. Also, even if the ratio t1/t2 is less than 0.2, the effect of improving ride comfort during normal running cannot be sufficiently obtained. On the other hand, if the ratio t1/t2 is more than 3, the durability during run-flat running may deteriorate. Further, even if the elasticity of a part of the side reinforcing rubber 6 is reduced, the weight does not increase, so the fuel efficiency is not impaired.
- the maximum tire width in the reference state is equal to or more than the center value of the maximum tire width defined by the standard and equal to or less than the upper limit value, and the tire maximum width position in the reference state is located radially outward from the bead base line in the tire cross section. Positioning it radially outward of the position spaced apart by 50% of the height reduces the radius of curvature of the carcass line in the buttress portion, reduces the tension of the carcass ply, and reduces the bending rigidity of the buttress portion. can. As a result, deterioration in riding comfort can be further suppressed.
- the run-flat tire of the present embodiment by reducing the tension of the carcass ply and lowering the elastic modulus of the side reinforcing rubber in the buttress portion, the flexural rigidity of the buttress portion is moderately increased. It is possible to suppress deterioration in fuel efficiency and ride comfort while ensuring run-flat durability.
- the low-elasticity portion 6b be located outside the other portion 6a in the tire width direction in a tire radial region of 50% or more and 80% or less of the tire cross-sectional height from the bead base line. This is because detachment from the rim during run-flat running can be suppressed.
- the other portion 6a is positioned at the tire radial position, which is the tire maximum width position. This is because the position of the maximum width of the tire greatly contributes to load support during run-flat running, so durability during run-flat running can be further ensured.
- the elastic modulus of the low elastic portion 6b is preferably 50% or less, more preferably 20% or less, of the elastic modulus of the other portion 6a. This is because the ride comfort during normal running can be further improved.
- FIG. 2 is a tire width direction partial cross-sectional view of a run-flat tire according to another embodiment of the present invention.
- the tire 11 of this embodiment has an inner liner 7 on the inner surface of the tire.
- the inner liner 7 is made of butyl rubber.
- an inner layer rubber 8 is arranged between the side reinforcing rubber 6 and the inner liner 7 .
- the inner layer rubber 8 is arranged over substantially the entire region where the side reinforcing rubber 6 and the inner liner 7 are adjacent to each other.
- the inner layer rubber 8 conforms to JIS K6270: 2001, using a test piece in which the center part of a No.
- dumbbell is notched 1 mm perpendicular to the direction of repeated tension of the test piece, and is repeatedly pulled at a frequency of 10 Hz under conditions of 150 ° C. is applied, the number of repetitions until the test piece breaks is twice or more (preferably 10 times or more) that of the side reinforcing rubber 6 in the applied tensile strain range of 10% to 30%.
- the inner layer rubber 8 is made of rubber that does not contain a copolymer of isobutylene and isoprene. Since it is the same as that of FIG. 1 except that the inner layer rubber 8 is arranged, the description of other configurations is omitted.
- the ratio of the elastic modulus of the inner layer rubber 8 to the elastic modulus of the other portion 6a of the side reinforcing rubber 6 is 0.75 or less (preferably 0.6 or less).
- the ratio of the thickness of the inner layer rubber 8 measured in the direction of the perpendicular to the thickness of the inner rubber layer 8 (consisting of the low elastic portion 6b) is 0.05 to 0.30.
- the inner layer rubber 8 is made according to JIS K6270: 2001, using a test piece in which the center part of a No. 8 dumbbell is notched 1 mm perpendicular to the direction of repeated tension of the test piece, and is repeatedly pulled at a frequency of 10 Hz under conditions of 150 ° C. is applied, the number of repetitions until the test piece breaks is twice or more (preferably 10 times or more) that of the side reinforcing rubber 6 in the applied tensile strain range of 10% to 30%. Therefore, the inner layer rubber 8 has high crack resistance. During run-flat running, the innermost part of the reinforced rubber is in a state of high temperature and high strain due to large deflection.
- the fracture resistance of the side reinforcing rubber can be enhanced, and the runflat durability can be further improved.
- the inner layer rubber 8 is made of a rubber that does not contain a copolymer of isobutylene and isoprene (for example, a rubber blended with butadiene rubber and natural rubber), the side reinforcing rubber 6 and the inner liner 7 are more efficient than butyl rubber or the like.
- the inner layer rubber 8 as described above is less susceptible to cracking than butyl rubber or the like, and therefore is less likely to generate nuclei of cracks that may extend to the side reinforcing rubber 6. Since the generated crack does not easily propagate to the inner layer rubber 8, the propagation of the crack from the inner liner 7 to the side reinforcing rubber 6 can also be suppressed. As a result, it is possible to suppress deterioration in load bearing capacity due to cracks occurring in the side reinforcing rubbers 6 which play a role of supporting the load during run-flat running.
- the ratio of the modulus of elasticity of the inner layer rubber 8 to the modulus of elasticity of the other portion 6a of the side reinforcing rubber 6 is 0.75 or less, it is possible to prevent deterioration of ride comfort during normal running. can.
- the inner layer rubber 8 when measured in the direction of the perpendicular to the maximum thickness of the side reinforcing rubber 6 when measured in the direction of the perpendicular drawn from the carcass 4 to the inner surface of the tire
- the thickness ratio to 0.05 or more, it is possible to more effectively obtain the effect of suppressing the decrease in load bearing capacity.
- the maximum thickness of the side reinforcing rubber 6 when measured in the direction of the perpendicular drawn from the carcass 4 to the inner surface of the tire is the maximum thickness when measured in the direction of the perpendicular.
- the maximum width position of the mold was set at 52% of the tire cross-sectional height from the bead base to the outside in the tire radial direction.
- the low-elasticity portion having an elastic modulus of 75% compared to the side reinforcement rubber is placed in the range of 61% to 73% of the tire cross-sectional height from the bead base line in the tire radial direction, and the maximum thickness of the gauge of the low-elasticity portion.
- the structure was arranged so that the ratio of the low-elasticity part gauge/rubber gauge of the other part was 0.5. Others are the same as those of the comparative example.
- the inner layer rubber having an elastic modulus of 31% compared to the side reinforcing rubber is arranged so that the ratio of the gauge of the inner layer rubber/the gauge of the side reinforcing rubber is 0.14 at the thickest part of the side reinforcing rubber gauge.
- Other configurations are the same as those of the comparative example.
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Abstract
Description
(1)トレッド部と、
前記トレッド部の両側に連なる一対のサイドウォール部と、
前記各サイドウォール部に連なるビード部と、
前記サイドウォール部に配設された断面三日月状のサイド補強ゴムと、
一対の前記ビード部間でトロイダル状に跨るカーカスと、を備えた、ランフラットタイヤであって、
前記サイド補強ゴムの一部は、他の部分よりも弾性率の低い低弾性部であり、
前記低弾性部は、前記ランフラットタイヤを適用リムに装着し、規定内圧を充填し、無負荷とした、基準状態において、ビードベースラインからタイヤ断面高さの50%以上80%以下のタイヤ径方向領域に位置し、
前記低弾性部の弾性率は、前記他の部分の弾性率の80%以下であり、
前記基準状態におけるタイヤ幅方向断面において、前記低弾性部の、前記カーカスからタイヤ内面に下ろした垂線の方向に計測した際の厚さが最大となる最大厚さをt1とし、前記垂線の方向に計測した際の前記他の部分の厚さをt2とするとき、比t1/t2は、0.2以上3以下であり、
前記基準状態におけるタイヤ最大幅は、規格で規定されるタイヤ最大幅の中心値以上上限値以下であり、
前記基準状態におけるタイヤ最大幅位置は、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの50%離間した位置よりもタイヤ径方向外側に位置することを特徴とする、ランフラットタイヤ。
また、本明細書において、「適用リム」とは、タイヤが生産され、使用される地域に有効な産業規格であって、日本ではJATMA(日本自動車タイヤ協会)のJATMA YEAR BOOK、欧州ではETRTO(The European Tyre and Rim Technical Organisation)のSTANDARDS MANUAL、米国ではTRA(The Tire and Rim Association,Inc.)のYEAR BOOK等に記載されているまたは将来的に記載される、適用サイズにおける標準リム(ETRTOのSTANDARDS MANUALではMeasuring Rim、TRAのYEAR BOOKではDesign Rim)を指す(即ち、上記の「リム」には、現行サイズに加えて将来的に上記産業規格に含まれ得るサイズも含む。「将来的に記載されるサイズ」の例としては、ETRTO 2013年度版において「FUTURE DEVELOPMENTS」として記載されているサイズを挙げることができる。)が、上記産業規格に記載のないサイズの場合は、タイヤのビード幅に対応した幅のリムをいう。また、「規定内圧」とは、上記JATMA等に記載されている、適用サイズ・プライレーティングにおける単輪の最大負荷能力に対応する空気圧(最高空気圧)を指し、上記産業規格に記載のないサイズの場合は、「規定内圧」は、タイヤを装着する車両毎に規定される最大負荷能力に対応する空気圧(最高空気圧)をいうものとする。
また、タイヤ最大幅に関する「規格」は、上記のタイヤが生産され、使用される地域に有効な産業規格をいうものとする。
また、「ビードベースライン」とは、上記基準状態において、ビードベースを通りタイヤ幅方向に平行な仮想線をいうものとする。
さらに、このタイヤ1では、上記基準状態におけるタイヤ最大幅位置は、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの50%離間した位置よりもタイヤ径方向外側に位置している。上記基準状態におけるタイヤ最大幅位置は、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの50%離間した位置よりタイヤ径方向外側、且つ、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの60%離間した位置又はそれよりタイヤ径方向内側とすることができる。あるいは、上記基準状態におけるタイヤ最大幅位置は、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの60%離間した位置よりタイヤ径方向外側とすることもできる。
そして、図示のように、カーカスラインは、タイヤ外表面のプロファイルに略沿った形状をなしている。
以下、本実施形態のランフラットタイヤの作用効果について説明する。
さらに、上記基準状態におけるタイヤ最大幅が、規格で規定されるタイヤ最大幅の中心値以上上限値以下であり、上記基準状態におけるタイヤ最大幅位置が、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの50%離間した位置よりもタイヤ径方向外側に位置することにより、バットレス部におけるカーカスラインの曲率半径を小さくし、カーカスプライの張力を低減してバットレス部の曲げ剛性を低減させることができる。これにより、乗り心地性の低下をさらに抑制することができる。
以上のように、本実施形態のランフラットタイヤによれば、バットレス部において、カーカスプライの張力を低減し、且つ、サイド補強ゴムの弾性率を低くすることによって、バットレス部の曲げ剛性を適度に低減して、ランフラット耐久性を確保しつつも、燃費性の低下及び乗り心地性の低下を抑制することができる。
また、上記基準状態において、上記カーカス4からタイヤ内面に下ろした垂線の方向に計測した際のサイド補強ゴム6の厚さが最大となる最大厚さ(他の部分6aのみ又は他の部分6aと低弾性部6bとからなる)に対する、上記垂線の方向に計測した際の内層ゴム8の厚さの比は、0.05~0.30である。
また、内層ゴム8は、イソブチレンとイソプレンとの共重合体を有しないゴム(例えばブタジエンゴムと天然ゴムを配合したゴム)からなるため、ブチルゴム等との対比で、サイド補強ゴム6及びインナーライナー7との接着性が高く、高温且つ大きな圧縮歪が生じるランフラット走行時においても、サイド補強ゴム6及びインナーライナー7との剥離が生じにくい。従って、サイド補強ゴム6とインナーライナー7とが内層ゴム8を介して接着したままの状態を保つことができる。これにより、サイド補強ゴム6とインナーライナー7とが剥離することによるサイドウォール部2の曲げ剛性の低下に起因する荷重支持能力の低下を抑制することができる。
さらに、上記のような内層ゴム8は、ブチルゴム等との対比で、亀裂が発生しにくく、従って、サイド補強ゴム6へ進展する可能性のある亀裂の核が生じにくく、また、インナーライナー7に生じた亀裂が内層ゴム8までは進展しにくいことから、インナーライナー7からサイド補強ゴム6への亀裂の進展も抑制することができる。これにより、ランフラット走行時に荷重支持の役割を果たすサイド補強ゴム6に亀裂が発生することによる荷重支持能力の低下も抑制することができる。
加えて、サイド補強ゴム6の他の部分6aの弾性率に対する、内層ゴム8の弾性率の比は、0.75以下であるため、通常走行時の乗り心地性を低下させないようにすることもできる。
一方で、上記基準状態において、上記カーカス4からタイヤ内面に下ろした垂線の方向に計測した際のサイド補強ゴム6の厚さが最大となる最大厚さに対する、上記垂線の方向に計測した際の内層ゴム8の厚さの比を0.30以下とすることで、内層ゴム8を追加したことによる重量増を極力抑えることができる。
本発明の効果を確かめるため、タイヤサイズPSR 235/40R19の発明例及び比較例にかかるタイヤを試作して、タイヤ性能を評価する試験を行った。
比較例:サイド補強ゴムを1種類のゴムからなるものとした。モールドの最大幅位置は、ビードベースからタイヤ径方向外側にタイヤ断面高さの48%の位置とした。モールドの最大幅は、なお、規格で規定されるタイヤ最大幅の中心値未満とした。
発明例:モールドの最大幅(タイヤ最大幅に対応)を比較例より11.4mm大きくした。なお、規格で規定されるタイヤ最大幅の中心値以上上限値以下である。モールドの最大幅位置は、ビードベースからタイヤ径方向外側にタイヤ断面高さの52%の位置とした。また、サイド補強ゴム対比75%の弾性率を有する低弾性部を、タイヤ径方向にビードベースラインからタイヤ断面高さの61%~73%の範囲に、かつ、低弾性部のゲージの最厚部において低弾性部ゲージ/他の部分のゴムゲージの比が0.5となるように配置した構造とした。その他は比較例と同様である。さらに、サイド補強ゴム対比31%の弾性率を有する内層ゴムを、サイド補強ゴムゲージ最厚部において内層ゴムのゲージ/サイド補強ゴムのゲージの比が0.14となるように配置した構造とした。その他の構成は、比較例と同様である。
ISO規格に準拠したリム、内圧、及び荷重条件において、ランフラット耐久性を評価した。比較例の結果を100とした指数で表示し、指数が大きい方が性能に優れている。
<縦バネ係数>
JATMAに準拠したリムにリム組みし、230kPaの内圧を充填し、4320Nの荷重を負荷した際の縦バネ係数を算出した。比較例の結果を100とした指数で表示し、指数が小さい方が性能に優れている。
評価結果を以下の表1に示している。
11:ランフラットタイヤ、
1:トレッド部、
2:サイドウォール部、
3:ビード部、
4:カーカス、
5:ベルト、
6:サイド補強ゴム、
7:インナーライナー、
8:内層ゴム
Claims (5)
- トレッド部と、
前記トレッド部の両側に連なる一対のサイドウォール部と、
前記各サイドウォール部に連なるビード部と、
前記サイドウォール部に配設された断面三日月状のサイド補強ゴムと、
一対の前記ビード部間でトロイダル状に跨るカーカスと、を備えた、ランフラットタイヤであって、
前記サイド補強ゴムの一部は、他の部分よりも弾性率の低い低弾性部であり、
前記低弾性部は、前記ランフラットタイヤを適用リムに装着し、規定内圧を充填し、無負荷とした、基準状態において、ビードベースラインからタイヤ断面高さの50%以上80%以下のタイヤ径方向領域に位置し、
前記低弾性部の弾性率は、前記他の部分の弾性率の80%以下であり、
前記基準状態におけるタイヤ幅方向断面において、前記低弾性部の、前記カーカスからタイヤ内面に下ろした垂線の方向に計測した際の厚さが最大となる最大厚さをt1とし、前記垂線の方向に計測した際の前記他の部分の厚さをt2とするとき、比t1/t2は、0.2以上3以下であり、
前記基準状態におけるタイヤ最大幅は、規格で規定されるタイヤ最大幅の中心値以上上限値以下であり、
前記基準状態におけるタイヤ最大幅位置は、ビードベースラインからタイヤ径方向外側にタイヤ断面高さの50%離間した位置よりもタイヤ径方向外側に位置することを特徴とする、ランフラットタイヤ。 - タイヤ内面にインナーライナーを備え、
前記サイド補強ゴムと前記インナーライナーとの間に、内層ゴムが配置され、
前記内層ゴムは、JIS K6270:2001に準じ、8号ダンベルの中心部を試験片繰り返し引張方向と垂直に1mm切り欠いた試験片を用いて、150℃の条件下で、10Hzの周波数で繰り返し引張を与えた際に、試験片が破壊するまでの繰り返し回数が、与えた引張歪が10%~30%の範囲において、前記サイド補強ゴムの場合の2倍以上である、請求項1に記載のランフラットタイヤ。 - タイヤ内面にインナーライナーを備え、
前記サイド補強ゴムと前記インナーライナーとの間に、内層ゴムが配置され、
前記内層ゴムは、イソブチレンとイソプレンとの共重合体を有しないゴムからなる、請求項1又は2に記載のランフラットタイヤ。 - 前記サイド補強ゴムの前記他の部分の弾性率に対する、前記内層ゴムの弾性率の比は、0.75以下である、請求項2又は3に記載のランフラットタイヤ。
- 前記基準状態において、前記垂線の方向に計測した際の前記サイド補強ゴムの厚さが最大となる最大厚さに対する、前記垂線の方向に計測した際の前記内層ゴムの厚さの比は、0.05~0.30である、請求項2~4のいずれか一項に記載のランフラットタイヤ。
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