JP2007045354A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability of a bead part of a pneumatic tire by extending a developable distance of crack developing along a steel cord of a reinforcing layer, and suppressing generation and development rate of the crack. <P>SOLUTION: The reinforcing layer 40 which is longer than a carcass layer 30 in a tire radial direction is disposed at the outside of a folded part 32 of the carcass layer 30 of the bead part. A plurality of steel cords 44 embedded in the reinforcing layer 40 are bent in a wave shape having the predetermined half amplitude, and the center line T of the amplitude is inclined by a predetermined angle theta with respect to the tire circumferential line C. The developable distance near to the end part 33 of the carcass layer of the crack along the steel cord 44 is extended thereby, and the generation and the development rate of the crack are suppressed by giving retractility to the steel cord 44. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire provided with a reinforcing layer outside a carcass layer of a bead portion, and more particularly, a pneumatic tire in which a cord embedded in the reinforcing layer is bent into a wave shape to improve the durability of the bead portion. Regarding tires.

  A pneumatic tire generally includes a pair of bead cores and a carcass layer including at least one carcass ply extending between them in a toroidal shape, and a plurality of reinforcing cords are provided inside the carcass ply. Buried. Both ends of the carcass layer are usually folded and fixed so as to wrap the bead core in order to prevent the carcass layer from being pulled out of the bead core due to tensile stress applied to the ply cord.

FIG. 4 is a sectional view showing an example of the structure of such a conventional bead unit 100, although it is not described in the patent literature.
As shown in the figure, the conventional bead portion 100 has a structure in which the end portion of the carcass layer 101 is largely folded around the bead core 102 from the inner side in the tire width direction (left side in the figure) to the outer side (right side in the figure). The folded portion 101a is embedded and fixed in rubber. As a result, when the tire is assembled to the rim and filled with internal pressure (hereinafter referred to as internal pressure filling), or when the vehicle rolls under a load such as when traveling on the road surface (hereinafter referred to as load loaded rolling) In addition, the ply cord is prevented from being pulled out from the bead core 102.

  However, in the conventional pneumatic tire having the structure of the bead portion 100, the carcass layer 101 is folded back at the time of internal pressure filling or load load rolling due to a rigidity step of each member as described below. A large shear strain is generated in the tire radial outer end portion (upper end portion in the figure) 101b of the portion 101a and a crack is generated in the portion, and the crack develops in the tire circumferential direction over time and is connected to each other. The bead unit 100 may be destroyed (failed).

  That is, when the tire is filled with the internal pressure, a compression force acts on the rubber of the bead back surface portion 104 sandwiched between the folded portion 101a of the carcass layer 101 and the rim flange 103 by the internal pressure due to the internal pressure and the reaction force received from the rim flange 103. . However, since the rubber is incompressible, the rubber of the bead back surface portion 104 corresponds to the compressive force toward the outer side in the tire radial direction (the upper side in the figure) from the rim flange tip portion 103a which is a portion where the compressive force does not act. Flows as much as the deformation that occurs. Since the carcass layer 101 reinforced with a high-rigidity cord such as steel is not easily deformed even when subjected to the compressive force, the flowable rubber has a gap between the end 101b of the folded portion 101a and the flowing rubber. A large shear strain is generated. In particular, in the case of a tire that is used at a high internal pressure, such as a heavy-duty pneumatic radial tire for trucks and buses, the amount of compressive force and the amount of rubber flowing increases, so that the generated shear strain increases.

  In addition, when rolling under load, the tread that touches the road surface deforms into a flat shape in accordance with the road surface shape, and the pair of sidewall portions above the ground surface also increase toward the outer side of the tire width following the deformation. Deforms and deforms. This bending deformation propagates to the bead portion 100 connected to the sidewall portion, and the tire radial direction outer side (upper side in the drawing) portion 100a of the bead portion 100 faces the outer side in the tire width direction (right side in the drawing). Therefore, a so-called falling phenomenon of the bead portion 100 that deforms so as to fall down occurs. Accompanying this phenomenon, a pulling force in the direction of arrow T in the figure acts on the carcass layer 101, and a large shear strain is generated at the end 101b.

  In addition, the belt layer located on the outer peripheral side of the carcass layer 101 is largely deformed in the tire circumferential direction at the tread contact surface, particularly at the stepped-on portion and the kicked-out portion of the tread contact surface during rolling under load. A tensile force in a substantially circumferential direction acts on the sidewall portion, and the side wall portion is greatly deformed in the same direction. As a result of this deformation being transmitted and the bead portion 100 also being deformed in the substantially circumferential direction, shear strain in the tire circumferential direction also occurs at the end portion 101b of the carcass layer 101.

  As described above, in the bead portion 100 having this conventional structure, a large shear strain is generated at the end portion 101b of the carcass layer folded portion 101a, and therefore a failure nucleus such as a crack that causes the failure of the bead portion 100 is generated in the vicinity thereof. There is a problem that it is easy. Further, when this failure nucleus occurs, the shear stress input at the time of load load rolling or the like is used as a driving force, cracks propagate in the circumferential direction in the bead portion 100 and are connected to each other. However, there is a problem that failure is likely to occur.

  The occurrence of such a failure not only hinders the complete running of a new tire, but also hinders the realization of a request for extending the life of the tire including the tread correction (recapping). That is, in order to prolong the life of the tread, perform correction, and increase the number of executions, the bead unit 100 has high durability enough to withstand long-term use, and does not change from when it is new even after long-term use. It is required to exhibit sufficient performance.

  In response to these demands, a reinforcing layer called a wire chafer is arranged in the bead part, and the air that has improved the durability of the bead part by addressing the above-mentioned problems by reducing the shear strain at the end of the carcass layer, etc. An entering tire is known (see Patent Document 1).

FIG. 5 is a half-sectional view in the width direction showing the structure of the conventional pneumatic tire 110.
In addition to the structure of the bead portion 100 shown in FIG. 4, the bead portion 100 of the pneumatic tire 110 has a plurality of steel cords on the outer side of the carcass layer 101 folded around the bead core 102 as shown in the figure. The reinforcing layer 105 is embedded in. The cord of the reinforcing layer 105 is inclined at a predetermined angle with respect to the tire circumferential line, and the outer portion 105a disposed so as to overlap the folded portion 101a of the carcass layer 101 located on the outer side in the tire width direction (left side in the drawing). Is made longer than the folded portion 101a of the carcass layer 101, and the end portion 105b thereof is disposed on the outer side in the tire radial direction (upper side in the drawing) than the end portion 101b of the carcass layer.

  In this conventional pneumatic tire 110, the reinforcing layer 105 is provided to reinforce the bead core 102 and the carcass layer 101, particularly the folded portion 101a, and protect them from impacts and friction received from the rim flange. The rigidity of the part 100 can be increased, and the above-described rubber flow at the time of filling with internal pressure, the falling-down at the time of load-load rolling, and the deformation in the circumferential direction can be suppressed. At this time, the end portion 105b is positioned higher than the end portion 101b of the carcass layer 101, and various shear stresses in the vicinity thereof are received by the cords in the reinforcing layer 105. It is also possible to suppress deformation that occurs in the vicinity of the portion 101b, reduce shear strain in the circumferential direction, and suppress occurrence of cracks and the like in that portion.

  However, in the vicinity of the end portion 105b of the reinforcing layer 105 that receives shear stress in place of the carcass layer 101, shear strain similar to that generated in the end portion 101b of the carcass layer 101 is generated, and cracks or the like are generated in that portion. Failure nuclei are likely to occur. That is, the location where the shear strain and the failure nucleus are generated moves to the vicinity of the end portion 105b of the reinforcing layer 105. In the structure of the conventional cord portion 100, even if a crack occurs, the crack propagates in the circumferential direction. Without progressing, it progresses along the cord in the reinforcing layer 105 toward the inner side in the tire radial direction (lower side in the figure). Therefore, in the structure of the bead portion 100, the cracks of the cords of the reinforcing layer 105 are independent from each other while progressing along the cords, and the major faults such as the fact that they are developed and connected in the circumferential direction. Is less likely to occur.

  However, when the crack that has developed along the cord of the reinforcing layer 105 reaches the vicinity of the end portion 101b of the carcass layer 101, the crack tends to move away from the cord and move toward the end portion 101b of the carcass layer 101. As described above, the cracks propagate in the circumferential direction and a large failure is likely to occur in the bead portion 100.

  However, in this bead portion 100, the end portion 105b of the reinforcing layer 105, where the crack is generated, is arranged farther outward in the tire radial direction (upper side in the drawing) than the end portion 101b of the carcass layer 101, and is reinforced. The cord of the layer 105 is inclined at a predetermined angle with respect to the circumferential direction, so that the distance along the cord between the end portions 105b and 101b (the crack propagation distance) is increased. Accordingly, the distance and the time required for the crack to propagate from the occurrence location to the end portion 101b of the carcass layer 101 become longer, and the occurrence of a major failure in the bead portion 100 can be delayed.

  As described above, by disposing such a reinforcing layer 105 on the bead portion 100, it is possible to suppress the occurrence of a major failure in the bead portion 100, and thus the durability can be improved. However, in recent years, it has been desired to further extend the life of the tire including an increase in the number of corrections. To that end, it is necessary to further improve the durability of the bead portion 100.

  In addition to the above, as a pneumatic tire with improved durability of the bead portion, a longer reinforcing layer is disposed outside the folded portion of the carcass layer, and a steel cord embedded in the reinforcing layer is used. There is also known one whose shape is bent into a wave shape (see Patent Document 2).

  In this conventional pneumatic tire, a reinforcing layer in which a plurality of steel cords bent in a corrugated shape are arranged in parallel to each other is arranged from the bottom surface of the bead portion to the sidewall portion, and the cord using the stretchability of the corrugated cord The rigidity difference between the rubber and the rubber is alleviated and the occurrence of cracks is suppressed to improve the durability of the bead portion and the like. That is, the wave-shaped cord is deformed so that the amplitude is small (long wavelength) when the tensile stress is applied, and is deformed so that the amplitude is large (short wavelength) when the compressive stress is applied. Therefore, the stress concentration at the end of the cord is relaxed and the occurrence of cracks at that portion is suppressed.

  However, in this conventional pneumatic tire, the specific shape of the corrugated cord is not defined at all, and if a crack occurs at one end, the crack propagates in the tire circumferential direction as in the conventional case, and the bead is There is a risk of failure in parts. In other words, no consideration is given to the progress of cracks along the cord and the securing of the distance that can be propagated by setting an appropriate corrugated cord shape, etc. Therefore, in this reinforcing layer structure, an effective bead portion Durability cannot be improved.

JP 2005-162022 A JP 51-91506 A

  The present invention has been made in view of the above-described conventional problems, and an object thereof is a crack that propagates along a steel cord of a reinforcing layer in a pneumatic tire including a reinforcing layer outside a carcass layer of a bead portion. It is to improve the durability of a bead part by lengthening the distance which can be propagated and suppressing the generation | occurrence | production and progress rate of a crack.

The invention according to claim 1 is a carcass layer having a pair of bead cores, a main body portion extending between the bead cores in a toroidal shape, and a turn-up portion wound around the bead core from the inner side to the outer side in the tire width direction, and the vicinity of the bead core A reinforcing layer in which a plurality of steel cords are embedded in the tire width direction along the folded portion outside the carcass layer, and in the tire radial direction of the reinforcing layer along the folded portion In the pneumatic tire in which the outer end portion is disposed on the outer side in the tire radial direction than the outer end portion in the tire radial direction of the folded portion, the steel cord is bent in a wave shape, and the half amplitude of the waveform is represented by A and the wavelength. When λ, 0.12 ≦ 2 × A / λ ≦ 1.2.
According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, when the inclination angle of the center line of the amplitude of the steel cord with respect to the tire circumferential line is θ, 10 ° ≦ θ ≦ 40 °, or 140 ° ≦ θ ≦ 170 °.
According to a third aspect of the present invention, in the pneumatic tire according to the first or second aspect, a height in a tire radial direction from a rim radial position to a tire radial direction outer end portion of the reinforcing layer is divided by a tire cross-sectional height. 0.10 ≦ M / B ² ≦ 0.75, where B is the measured value and M is the treat bending rigidity of the reinforcing layer.

(Function)
According to the present invention, in a pneumatic tire provided with a reinforcing layer outside the carcass layer of the bead portion, the steel cord, which is a crack propagation path, is bent into a corrugated shape, thereby increasing the crack propagation distance. In addition, the steel cord is deformed following the deformation of the surrounding rubber to reduce the rigidity step with the rubber, the stress concentration at the end of the steel cord and the shear strain at the portion are alleviated, and the occurrence of cracks is suppressed. At the same time, the shear input, which is the driving force for propagating cracks, is relaxed, and the crack growth rate is slowed. In addition, by setting the inclination angle of the center line of the steel cord amplitude and the height of the outer part of the reinforcing layer, etc., it is possible to lengthen the crack propagation distance and ensure that the crack follows the steel cord. Make progress and prevent breakage of steel cord.

  According to the present invention, since the steel cord embedded in the reinforcing layer is bent into a corrugated shape, the possible crack propagation distance can be increased. In addition, since the steel cord can be deformed following the deformation of the rubber, the step difference in rigidity with the surrounding rubber can be reduced, and the stress concentration at the end of the steel cord and the shear strain at that portion can be alleviated to suppress the occurrence of cracks. At the same time, the crack driving force can be relaxed and the crack growth rate can be slowed. Further, the crack can be reliably propagated along the steel cord, and the steel cord can be prevented from being broken. Therefore, it is possible to suppress the occurrence of large breakage in the bead portion, and it is possible to effectively improve the durability of the bead portion.

Hereinafter, an embodiment of a pneumatic tire of the present invention will be described with reference to the drawings.
Like the conventional pneumatic tire 110 shown in FIG. 5, the pneumatic tire 1 of the present invention improves the durability of the bead portion by folding the carcass layer around the bead core of the bead portion and arranging a reinforcing layer on the outside thereof. However, the cord of the reinforcing layer is bent into a wave shape, etc., so that the distance that the crack can propagate is lengthened, the stress concentration at the end of the cord is relaxed, and the occurrence of cracks is suppressed. Improved.

FIG. 1 is a half-sectional view in the width direction showing the structure of the pneumatic tire of the present embodiment.
As shown in the figure, the pneumatic tire 1 of the present embodiment has a substantially cylindrical tread portion 3 having a tread pattern 2 formed on the outer peripheral surface, and the tire radial direction inner side (lower side in the figure) from both ends thereof. And a pair of bead portions 5 (shown only on one side in the drawing) positioned on the inner side in the tire radial direction of the sidewall portion 4.

  In addition, the pneumatic tire 1 includes a pair of bead cores 6 disposed in the vicinity of the inner end in the tire radial direction of the bead portion 5, and is folded around the bead core 6 and extends in a toroidal shape between the pair of bead cores 6. The carcass layer 30, the reinforcing layer 40 called a wire chafer extending along the outside of the carcass layer 30 of the bead portion 5, and the tire radial direction outer side (upper side in the drawing) of the carcass layer 30 in the tread portion 3. Belt layer 7.

  The bead core 6 is a ring-shaped member in which a plurality of steel wires or the like are wound. In addition to fixing both ends of the carcass layer 30, the bead core 6 holds internal air pressure and prevents the tire 1 from coming off the rim. Have. The belt layer 7 is formed by stacking a plurality of belt plies 8 (four in the figure) in which a plurality of steel cords, organic fiber cords, etc. are covered with rubber, in the tire radial direction, protecting the carcass layer 30 and treading. While strengthening the part 3, the rigidity in the circumferential direction is increased, and the effect is exhibited.

  The carcass layer 30 extends in a toroidal shape from the tread portion 3 through the sidewall portion 4 to the bead core 6 of the bead portion 5, and a body portion 31 that reinforces the portion, and the bead core 6 around the bead core 6 from the inner side in the tire width direction (see FIG. Then, it consists of a folded portion 32 which is folded from the left side toward the right side. The carcass layer 30 is composed of at least one carcass ply, and a plurality of non-stretchable reinforcing cords (ply cords), for example, steel cords, are embedded in the carcass ply. The carcass layer 30 of the present embodiment is composed of a single carcass ply in which a ply cord extending substantially in the radial direction (the meridian direction) is embedded.

  The reinforcing layer 40 is disposed so as to overlap the outer side of the carcass layer 30 in the vicinity of the bead core 6, and extends from the lower side of the bead core 6 to the outer side of the main body portion 31 of the carcass layer 30 (the left side which is the inner side in the tire width direction in the drawing). Tire diameter direction along the inner side 41 extending toward the outer side in the tire radial direction (upper side in the figure) and the outer side of the folded part 32 of the carcass layer 30 from the lower side of the bead core 6 (the right side that is the outer side in the tire width direction in the figure). The outer portion 42 extends outward in the direction.

  Here, the radial distance L (hereinafter referred to as the height L of the outer portion 42) from the rim diameter position S (bead heel) to the reinforcing layer end portion (radial outer end portion) 43 of the outer portion 42 is the rim diameter position. It is longer than the radial distance J (hereinafter referred to as the height J of the folded portion 32) from S to the carcass layer end portion (radially outer end portion) 33 of the folded portion 32. Therefore, like the conventional pneumatic tire 110 shown in FIG. 5, the reinforcing layer end 43 of the outer portion 42 is located on the outer side in the tire radial direction with respect to the carcass layer end 33 of the folded portion 32. The locations where shear strain and cracks occur during rolling under load can be moved from the carcass layer end portion 33 to the reinforcing layer end portion 43, and the generated cracks propagate along the cord of the reinforcing layer 40.

  FIG. 2 is an enlarged side view showing a part of the steel cord 44 embedded in the reinforcing layer 40, and FIG. 3 is an enlarged schematic view showing the vicinity of the reinforcing layer end 43 of the outer portion 42. As shown in FIG. is there.

  The reinforcing layer 40 is composed of at least one (here, one) reinforcing ply, and a steel cord 44 bent into a wave shape is embedded in the rubber of the reinforcing ply (reinforcing layer 40). . The steel cord 44 of this embodiment is obtained by bending a straight cord obtained by twisting a plurality of steel filaments into a sinusoidal shape having a single amplitude A and a wavelength λ as shown in FIG. Although it is formed, any wave shape other than a sine wave shape may be used as long as it has a constant half amplitude A and a wavelength λ and is bent while being smoothly curved.

  As shown in FIG. 3, the reinforcing layer 40 includes a plurality of the corrugated steel cords 44, and the amplitude center line T is inclined at a predetermined angle θ with respect to the tire circumferential line C so as to be parallel to each other. Thus, the amplitude A direction is arranged so as to face the same direction as the plane direction of the reinforcing ply, and is embedded in rubber so as not to contact each other. The figure also shows the ply cord 34 of the carcass layer 30 that extends substantially in the radial direction, but the reinforcing layer end 43 that is the end of the steel cord 44 is the end of the ply cord 34 as described above. It is arranged at a distance Q (see FIG. 1) away from the carcass layer end 33 toward the outer side in the tire radial direction (upper side in the figure).

  Here, when a crack occurs near the reinforcing layer end 43 as described above, the crack is directed along the steel cord 44 in the reinforcing layer 40 toward the inner side in the tire radial direction (lower side in FIG. 3). However, since the steel cord 44 of the present embodiment has a wave shape, the crack propagates in a wave shape along the steel cord 44. Therefore, in the reinforcing layer 40 of the present embodiment, the crack propagation path can be wave-shaped, and the crack is longer by the time it reaches the vicinity of the end portion 33 of the carcass layer than the conventional straight steel cord 44. It takes a path, that is, the crack propagation distance becomes long, and the crack progresses slowly to the vicinity of the end portion 33 of the carcass layer.

  Further, the corrugated steel cord 44 has elasticity. That is, when the tensile stress is applied, the piece amplitude A is deformed so as to be small (wavelength λ is long), and when the compressive stress is applied, the piece amplitude A is deformed so as to be large (wavelength λ is short). Can be deformed to follow. Therefore, the difference in rigidity between the steel cord 44 and the surrounding rubber is reduced, the stress concentration at the end of the steel cord 44 and the shear strain at that portion are alleviated, and the occurrence of cracks is suppressed. At the same time, since the shear input, which is the driving force for propagating the crack, is relaxed, the crack propagation speed is slowed.

  Therefore, in the pneumatic tire 1 of this embodiment having such a reinforcing layer 40, the occurrence of cracks is suppressed as compared with a conventional pneumatic tire provided with a reinforcing layer made of a linear steel cord, The advanceable distance is long and the advancement speed is slow, so that the occurrence of a large failure such as a crack connection can be suppressed, and the durability of the bead portion 5 can be improved.

  As described above, the corrugated steel cord 44 is formed so as to have a predetermined half amplitude A and a wavelength λ. However, a value obtained by dividing the half amplitude A by the wavelength λ (2 × When (A / λ) is less than 0.12, the half amplitude A becomes smaller (the wavelength λ becomes longer), and the steel cord 44 becomes nearly linear, so that the above-described crack propagation distance becomes shorter. The crack reaches the end portion 33 of the carcass layer earlier. At the same time, the stretchability of the steel cord 44 is reduced, the stress concentration near the end portion 43 and the shear strain are increased and cracks are easily generated, and the shear input which is the driving force for propagating the cracks is increased. The speed of crack growth increases. Therefore, the durability of the bead portion 5 may be reduced.

  When the value of 2 × A / λ is larger than 1.2, the half amplitude A becomes large (wavelength λ becomes short), and the steel cord 44 is bent more greatly. There is a risk that the cracks will not extend along the steel cord 44 and the path of progress will not be wavy. Therefore, the value of 2 × A / λ is preferably 0.12 or more and 1.2 or less (0.12 ≦ 2 × A / λ ≦ 1.2).

  If it is within this range, the wave shape of the steel cord 44 is optimized, the crack is surely propagated along the steel cord 44, and the advanceable distance is increased, and the steel cord 44 is appropriately expanded and contracted, The shear strain and crack growth driving force near the end 43 are reduced. Accordingly, the arrival of cracks near the carcass layer end portion 33 can be delayed, the generation and progress of cracks can be suppressed, and the durability of the bead portion 5 can be effectively improved.

  As described above, the center line T of the amplitude of the steel cord 44 is inclined at a predetermined angle θ (see FIG. 3) with respect to the tire circumferential line C. However, the inclination angle θ is less than 10 degrees or 170. If the angle is larger than the degree, that is, close to the direction of the circumferential line C, the crack may propagate away from the steel cord 44. Further, when θ is greater than 40 degrees and less than 140 degrees, that is, close to the direction orthogonal to the circumferential line C, the crack may possibly leave the steel cord 44 as described above, and the crack propagation distance , The cracks quickly reach the end portion 33 of the carcass layer, and the durability of the bead portion 5 may be reduced. Therefore, the inclination angle θ is preferably 10 degrees or more and 40 degrees or less, or 140 degrees or more and 170 degrees or less (10 ° ≦ θ ≦ 40 °, or 140 ° ≦ θ ≦ 170 °). If present, the crack can be reliably propagated along the steel cord 44.

  Furthermore, if the difference Q (see FIG. 1) between the height L of the outer portion 42 of the reinforcing layer 40 and the height J of the folded portion 32 of the carcass layer 30 is less than 10 mm, the reinforcing layer end 43 and the carcass layer end There is a possibility that the distance of the portion 33, that is, the distance at which the crack can progress is shortened, and the durability of the bead portion 5 is lowered. Therefore, it is preferable to set Q to 10 mm or more. In this case, the distance that the crack propagates before reaching the vicinity of the end portion 33 of the carcass layer becomes long, and the breakage of the bead portion 5 can be effectively suppressed.

Here, the value obtained by dividing the cross-sectional height of the tire by H (hereinafter referred to as tire height H) and the height L (see FIG. 1) of the outer portion 42 of the reinforcing layer 40 divided by the tire height H (L / H). ) Is B, treat bending rigidity of the reinforcing layer 40 is M, and F is a value obtained by dividing M by the square of the value B (M / B ² ). 0.10 ≦ F ≦ 0.75) is preferable. The reason is that if F is less than 0.10, the steel cord 44 may buckle and break when a compressive force is applied. On the other hand, if F is greater than 0.75, the compression may occur. This is because the steel cord 44 cannot be deformed following the deformation, the shear strain is remarkably increased, and the risk of a significant increase in the crack propagation speed along the steel cord 44 is increased.

  On the other hand, when F is set to 0.10 or more and 0.75 or less as described above, the crack propagation distance is increased while preventing breakage due to buckling of the steel cord 44 in the reinforcing layer 40. The progress speed can be reduced, and the durability of the bead portion 5 can be effectively improved. In addition, when the value of F is in the range of 0.15 or more and 0.40 or less, the above-described effect becomes more remarkable, which is preferable.

Here, the treat bending stiffness M of the reinforcing layer 40 is a value obtained by multiplying the bending stiffness of one steel cord 44 by the number of cords driven per 50 mm, and its unit is N · m ² . Note that the bending stiffness of the cord follows the formula shown in the following equation 1, that is, the well-known simple model calculation formula for the bending stiffness of the cord. Here, when the steel cord 44 has a double twist structure, a value obtained by adding the bending stiffness values in the respective layers is set as the bending stiffness of one steel cord 44 in accordance with the principle of the laminated beam.

In this equation, N is the number of filaments per layer, α is the twist angle of the filament (tan α = P / 2πR, where P is the cord twist pitch, R is the circumscribed circle diameter of each layer constituting the steel cord), and E is the filament Young's modulus of the (longitudinal elastic modulus), G is the modulus of transverse elasticity of the filament, I is the second moment ^{(I = πd 4/64)} , Ip is polar moment of inertia of area ^{(Ip = πd 3/32)} , d is The filament diameter, μf, is the Poisson's ratio of the filament.

  As described above, in the pneumatic tire 1 of the present embodiment, since the reinforcing layer 40 is provided outside the carcass layer 30 of the bead portion 5, the rigidity of the bead portion 5 is increased and deformation and the like during rolling under load are suppressed. it can. Further, since the reinforcing layer end portion 43 of the reinforcing layer outer portion 42 is positioned on the outer side in the tire radial direction from the carcass layer end portion 33 of the carcass layer folded portion 32, the shear strain near the carcass layer end portion 33 can be reduced, The locations where shear strain and cracks occur when rolling tires under load load can be moved from the carcass layer end portion 33 to the reinforcing layer end portion 43. Since the crack generated at the end portion 43 of the reinforcing layer propagates along the steel cord 44 in the reinforcing layer 40, it is possible to suppress the occurrence of large breakage in the bead portion 5 and improve the durability of the bead portion 5. .

  Further, in this embodiment, since the steel cord 44 is bent into a wave shape, the crack propagation distance to the vicinity of the end portion 33 of the carcass layer can be increased as compared with the conventional straight steel cord 44, and there is no crack. Can slow down to progress. In addition, since the steel cord 44 can be deformed following the deformation of the rubber, the rigidity step with the surrounding rubber can be reduced, and the stress concentration at the end of the steel cord 44 and the shear strain at that portion are alleviated to suppress the occurrence of cracks. it can. At the same time, the crack driving force can be relaxed, and the crack growth rate can be slowed. Therefore, compared with the conventional pneumatic tire, generation | occurrence | production of big failures, such as a connection of a crack, can be suppressed and durability of the bead part 5 can be improved.

  Furthermore, since the height L of the outer portion 42 of the reinforcing layer 40 and the inclination angle θ of the center line T of the amplitude of the steel cord 44 are optimized, the crack propagation distance is lengthened and the propagation speed is effective. Can be lowered. In addition to these, breakage due to buckling of the steel cord 44 in the reinforcing layer 40 can be prevented, and cracks can be reliably propagated along the steel cord 44, suppressing the breakage of the bead portion 5, Durability can be improved effectively.

(Example)
In order to confirm the effect of the pneumatic tire 1 of the present invention, the tire of the example (hereinafter referred to as an example product) provided with the reinforcing layer 40 having the structure described above is provided with a reinforcing layer 40 having a partly different structure. In addition, several types of conventional tires (hereinafter referred to as conventional products) including a reinforcing layer 40 having a conventional structure having a linear steel cord 44 and the following tires are manufactured according to the following conditions: Then, the durability of the bead portion 5 was tested.

  The following implementation products, comparative products, and conventional products are all heavy-duty radial tires of tire size 275 / 70R22.5 defined by JATMA YEAR BOOK (2004, Japan Automobile Tire Association Standard), and applicable rim is 7.50 × 22. .5. After these tires are mounted on the rim, the maximum air pressure of 900 kPa is filled, and a load of 5670 kg, which is 1.8 times the maximum load capacity of 3150 kg, is applied by a drum testing machine, while a speed of 1.7 km at a speed of 60 km / h. The load was continuously rolled on the drum until the bead portion 5 was broken, and the distance until the bead was broken was measured and compared. The result is shown as a life index with the travel distance of the conventional product 1 as 100.

In the table, the half amplitude A is the half amplitude (unit: mm) of the steel cord 44, the wavelength λ is the wavelength (unit: mm) of the steel cord 44, and the inclination angle θ (see FIG. 3) is the steel cord. 44 is an inclination angle (unit: degree) of the center line T with an amplitude of 44 with respect to the tire circumferential line C, and the distance Q (see FIG. 1) is the folded portion of the carcass layer 30 from the height L of the outer portion 42 of the reinforcing layer 40. The distance obtained by subtracting the height J of 32 (LJ, unit is mm), and the bending stiffness M is a treat bending stiffness M (unit: the bending stiffness of one steel cord 44 multiplied by the number of cords driven per 50 mm. Is N · m ² ), the value B (see FIG. 1) is a value obtained by dividing the height L of the outer portion 42 of the reinforcing layer 40 by the tire cross-sectional height H (L / H), and the value F is the reinforcement. A value obtained by dividing the treat bending rigidity M of the layer 40 by the square of the value B (M / B ² ).

  Table 1 shows the structural specifications and life index of the reinforcing layer 40 of one type of conventional product 1, eight types of implementation products (execution products 1 to 8), and five types of comparison products (comparison products 1 to 5). Show.

  As shown in Table 1, the life index of the implementation products 1 to 8 is 100 or more (the maximum value is 136 of the implementation product 3 and the minimum value is 105 of the implementation product 4) with respect to the life index 100 of the conventional product 1. On the other hand, all of the life indexes of the comparative products are lower than 100. Therefore, it can be seen that the durability index of the bead portion 5 is improved as compared with the conventional product. From this result, it was proved that the durability of the bead portion 5 of the pneumatic tire 1 is improved by the present invention.

It is a width direction half sectional view showing the structure of the pneumatic tire of this embodiment. It is a side view which expands and shows a part of code | cord | chord embed | buried under the reinforcement layer of this embodiment. It is a schematic diagram which expands and shows the edge part vicinity of the reinforcement layer outer side part of this embodiment. It is sectional drawing which shows the example of the structure of the conventional bead part. It is a width direction half sectional view which shows the structure of the conventional pneumatic tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pneumatic tire, 2 ... Tread pattern, 3 ... Tread part, 4 ... Side wall part, 5 ... Bead part, 6 ... Bead core, 7 ... Belt layer, 8 ... belt ply, 30 ... carcass layer, 31 ... main body, 32 ... folded portion, 33 ... end of carcass layer, 34 ... ply cord, 40 ... reinforcing layer , 41 ... inner part, 42 ... outer part, 43 ... reinforcing layer end, 44 ... steel cord.

Claims (3)

A pair of bead cores;
A carcass layer having a body portion extending in a toroidal manner between the bead cores and a folded portion wound around the bead cores from the inner side in the tire width direction toward the outer side;
The outer side of the carcass layer in the vicinity of the bead core, disposed along the folded portion to the inner side in the tire width direction, and a reinforcing layer having a plurality of steel cords embedded therein,
In the pneumatic tire in which the tire radial direction outer end portion of the reinforcing layer along the folded portion is disposed on the outer side in the tire radial direction than the tire radial direction outer end portion of the folded portion,
The pneumatic tire is characterized in that the steel cord is bent into a wave shape, and 0.12 ≦ 2 × A / λ ≦ 1.2, where A is a half amplitude of the waveform and λ is a wavelength. In the pneumatic tire according to claim 1,
A pneumatic tire characterized by satisfying 10 ° ≦ θ ≦ 40 ° or 140 ° ≦ θ ≦ 170 °, where θ is an inclination angle of the center line of the steel cord amplitude with respect to the tire circumferential line. In the pneumatic tire according to claim 1 or 2,
When the value obtained by dividing the height in the tire radial direction from the rim diameter position to the outer end in the tire radial direction of the reinforcing layer by the tire cross-sectional height is B, and the treat bending rigidity of the reinforcing layer is M,
A pneumatic tire characterized by satisfying 0.10 ≦ M / B ² ≦ 0.75.

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