JP4748522B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a mounting direction designation type pneumatic tire that employs an asymmetric tread to improve the rollover prevention performance of a vehicle.

  In recent years, demand for small passenger cars called so-called compact cars has been increasing for reasons such as economy and ease of handling. Since the compact car has a high vehicle height for a small vehicle width, there is a possibility of rollover when turning at high speed during cornering, and rollover prevention performance is required for the pneumatic tire to be mounted.

  In order to improve the rollover prevention performance, generally, the maximum value (CFmax) of the cornering force is reduced, or the CFmax value under the vehicle rear wheel mounting condition is increased with respect to the CFmax value under the vehicle front wheel mounting condition. The technique is taken.

  In order to reduce the CFmax value as in the former case, it is effective to lower the μ value (friction coefficient) of the tread rubber, but there arises a problem that the braking performance is lowered as a contradiction performance. In the latter method, the ratio between the CFmax value under the vehicle front wheel mounting condition and the CFmax value under the vehicle rear wheel mounting condition largely depends on the tire size, and it is generally the case that the ratio is changed by other factors. Have difficulty.

  On the other hand, a pneumatic tire in which tread rubber is divided into an inner side and an outer side when the vehicle is mounted and the rubber hardness of both is changed is known. For example, Patent Document 1 below discloses a friction coefficient ( It is disclosed that a high-hardness rubber having a larger μ value is disposed on the outer side of the divided tread. However, when a high hardness rubber having a larger friction coefficient (μ value) is provided on the outer side of the divided tread, it has been found to be counterproductive to improving the rollover prevention performance.

  Further, in Patent Document 2 below, a pneumatic tire is proposed in which a step is provided between a second rib (center side) and a shoulder rib (outside) formed on the tread surface to improve high-speed durability. ing. However, in this tire, the ground pressure on the inner shoulder of the tire during local high-speed driving due to the camber angle is suppressed by the second rib with a high surface, and rollover prevention performance is achieved by the dispersion of the ground pressure. It has been found that the improvement is adversely affected.

  On the other hand, Patent Document 3 below discloses a pneumatic tire that improves ride comfort and handling stability by disposing a belt end reinforcing ply in the vicinity of an outer shoulder portion when the vehicle is mounted. However, in this tire, since the round shape (that is, the meridian cross-sectional shape) of the outer and inner shoulder portions is symmetric, it is difficult to sufficiently improve the rollover prevention performance of the vehicle.

  In addition, so-called square shoulders that have an angular grounding end shape have been conventionally used to increase the grounding width, and no example of using a square shoulder to reduce the grounding width has been known to date. It was.

Japanese Patent Laid-Open No. 11-32237 JP 2000-238506 A Japanese Patent Laid-Open No. 11-32231

  Accordingly, an object of the present invention is to provide a pneumatic tire capable of improving the anti-overturning performance of a vehicle while maintaining the braking performance.

The above object can be achieved by the present invention as described below.
That is, the pneumatic tire of the present invention includes a pair of bead portions, sidewall portions extending outward from the bead portions in the tire radial direction, tread portions provided between the sidewall portions, and below the tread portions. In a pneumatic tire that is provided with a belt layer that is arranged and the mounting direction is specified, the distance from the center of the tread based on the tire maximum width to the inner ground contact edge when the vehicle is mounted under the front wheel mounting condition is D1, When the drop amount in the no-load state at the distance D1 of the inner shoulder is Di, the drop amount Do in the no-load state at a distance D1 from the center of the tread is larger than Di on the outside of the tread portion when the vehicle is mounted. An outer shoulder is formed, and the outer end of the belt layer when the vehicle is mounted is more rigid than the inner end. Wherein the is provided.

  In the present invention, the front wheel mounting condition refers to a condition in which the internal pressure of the tire is 230 kPa and a load of 70% of the maximum load load is applied in the vertical direction according to the tire size. Further, the maximum tire width refers to the maximum width in the axial direction measured on an unloaded condition with a specified air pressure attached to the applicable rim.

  According to the pneumatic tire of the present invention, an outer shoulder having a drop amount Do larger than Di is formed on the outer side when the tread portion is mounted on the vehicle, and the outer end portion of the belt layer is more rigid than the inner end portion. Since the belt reinforcing layer is provided, the outer ground contact area when the vehicle is mounted can be made smaller than that of the conventional tire during cornering. In other words, as shown in FIG. 2 (a), in a conventional symmetric tread tire (the belt reinforcement layer is also symmetric), the grounding end TEi on the inner shoulder side and the grounding end TEo on the outer side of the tire in the front wheel mounting condition are The distance from the center C of the tread with respect to a large amount is substantially the same. As shown in FIG. 2 (b), the ground contact surface in the front wheel mounting condition surrounded by the dotted line bulges outward during cornering, and has a contact surface shape surrounded by the solid line (the hatched portion is the area increasing portion). Such a ground contact surface causes a grip force of the tire. As in the present invention, the outer shoulder having a large drop amount Do is formed as described above, and a high rigidity belt reinforcing layer is provided at the outer end of the belt layer. Thus, as shown in FIG. 2 (c), the contact area during cornering can be reduced (the contact end TEo1 moves to TEo2), and the gripping force is reduced by that amount, thereby preventing the vehicle from overturning. Can be improved. In addition, according to this configuration, the ground contact area hardly changes during straight traveling or braking, and the braking performance can be sufficiently maintained.

  In the above, it is preferable that the inner shoulder is a round shoulder, and the outer shoulder is a stepped shoulder having a step portion so that the outside of the step portion is a non-grounding portion. By adopting such a shoulder with a step, it is possible to make the ground contact end TEo2 in FIG. 2 (c) further inside, further reducing the ground contact area during cornering and reducing the grip force accordingly. Thus, the rollover prevention performance of the vehicle can be further improved.

In that case, it is preferable that the boundary between the stepped portion and the tread surface is disposed at a distance of 93 to 110% of the distance D1 from the center of the tread. By setting the boundary in this range, it is possible to reduce the ground contact area more reliably with the ground end TEo2 inside.
The
Moreover, it is preferable that the boundary vicinity of the said level | step-difference part and a tread surface is formed of the square shoulder. According to the square shoulder, the boundary between the step portion and the tread surface can be clearly formed, and the contact area during cornering can be more reliably reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a meridian cross-sectional view showing an example of the pneumatic tire of the present invention, and FIG. 3 is a plan view showing an example of a tread pattern of the pneumatic tire of the present invention.

  As shown in FIG. 1, the pneumatic tire of the present invention includes a pair of bead portions 3, a sidewall portion 2 that extends outward from the bead portion 3 in the tire radial direction, and a tread portion 1 provided between the sidewall portions 2. And a belt layer 5 disposed below the tread portion 1. Such a structure is the same as that of a conventional pneumatic tire, and any conventionally known material, structure, and manufacturing method can be adopted except for the tread portion 1.

  For example, the carcass layer 6 is disposed between the pair of bead portions 3. The carcass layer 6 is a radial carcass formed from one layer obtained by rubberizing a cord such as polyester, and a rubber layer is formed outside the carcass layer 6. In the tubeless tire, the inner liner layer 4 is formed as the innermost layer. A belt layer 5 that reinforces the tire effect is disposed on the outer side in the tire radial direction of the carcass layer 6, and a tread portion 1 is formed on the outer side in the tire radial direction of the belt layer 5. The belt layer 5 is formed by laminating two layers of rubberized steel cords arranged in parallel at an inclination angle of about 20 ° with respect to the tire equator line C so that the steel cords intersect with each other across the tire equator line C. The

  Examples of the raw material of the tread rubber 9 forming the tread portion 1 include natural rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), butyl rubber (IIR) and the like. These rubbers are reinforced with fillers such as carbon black and silica, and a vulcanizing agent, a vulcanization accelerator, a plasticizer, an antiaging agent, and the like are appropriately blended.

  In the pneumatic tire of the present invention, as shown in FIG. 1, the distance from the tread center C based on the maximum tire width W to the inner grounding end TEi when the vehicle is mounted under the front wheel mounting condition is D1, and the inner shoulder When the drop amount in the no-load state at the distance D1 of 1a is Di, the outside when the tread portion 1 is mounted on the vehicle is the outside where the drop amount Do in the no-load state at the distance D1 from the center C of the tread is larger than Di. A shoulder 1b is formed.

  The drop amounts Do and Di in the present invention refer to the distance in the vertical direction at the position of the distance D1 with respect to the tangent when the tangent is drawn at the center C of the tread, as shown in FIG. In each figure, an arrow OUT indicates the outside when the tire is mounted on the vehicle in the specified mounting direction.

  The difference between the drop amounts Do and Di is preferably 1 mm or more, more preferably 2 mm or more, and further preferably 3 to 6 mm. If the difference between the drop amounts Do and Di is less than 1 mm, the effect of reducing the contact area during cornering tends to be small, and the rollover prevention performance of the vehicle tends to be insufficient.

  The specific drop amount Do of the outer shoulder 1b is preferably 4 to 17 mm, and more preferably 9 to 15 mm. Moreover, 3-12 mm is preferable and, as for the specific drop amount Di of the inner side shoulder 1a, 6-9 mm is more preferable.

  In the present embodiment, an example is shown in which the inner shoulder 1a and the outer shoulder 1b are formed of round shoulders. A round shoulder refers to a shoulder without a step on a groundable surface, and a shape having a curve in which a single arc or a plurality of arcs are continuous in a meridian section, a curve in which a radius of curvature is partially changed, or the like. Can be mentioned.

  When the outer shoulder 1b is a round shoulder, the drop amount Do in an unloaded state at the position of the distance D1 can be further increased by partially or entirely reducing the radius of curvature.

  Further, as shown in FIG. 1, the pneumatic tire of the present invention is provided with a belt reinforcing layer 24 having a rigidity higher than that of the inner end at the outer end when the belt layer 5 is mounted on the vehicle. Yes. The belt reinforcing layer 24 may be provided only on the outer end portion of the belt layer 5, but is preferably provided on the entire belt layer 5. In the present embodiment, an example is shown in which the entire upper surface of the belt layer 5 is covered with a lower belt reinforcing layer 24a, and an upper belt reinforcing layer 24b is further provided at the outer end when the vehicle is mounted. Thus, the outer end portion of the belt reinforcing layer 24 has a two-layer structure, so that the outer end portion has higher rigidity than the inner end portion.

  The belt reinforcing layer 24 is a reinforcing layer in which reinforcing fibers are arranged in the tire circumferential direction PD or a direction close to the tire circumferential direction PD. For example, the belt reinforcing layer 24 is formed by spirally winding one or more continuous cords or a plurality of cords in advance. And a ply formed in a sheet shape by covering with rubber. When the outer end portion has a two-layer structure, the cord winding and ply may be two layers.

  Examples of the cord used for the belt reinforcing layer 24 include polyester, aramid, rayon, nylon, PEN, and PBO. The number of cords driven into the belt reinforcing layer 24 is, for example, about 12 to 38 / inch. In the present invention, it is preferable to use a belt reinforcing layer 24 in which one end of a ply formed in a sheet shape is folded to have two outer end portions.

  The region in which the belt reinforcing layer 24 is partially made highly rigid preferably includes at least a range of 107 to 112% of the distance D1 from the center of the tread, and the range of a distance of 105 to 115%. Is more preferably included in at least the region.

  The pneumatic tire of the present invention is provided with a tread pattern T as shown in FIG. 3, for example, but the tread pattern T itself is not limited at all, and any conventionally known pattern can be adopted. In the illustrated example, the tread pattern T includes a thick circumferential groove 12 extending in the tire circumferential direction PD and a thin circumferential groove 14, and includes a plurality of inclined grooves 13 and a plurality of communication grooves 15 that communicate these. Yes.

  In the vicinity of the shoulder portion of the tread pattern T, a land portion having a plurality of inclined grooves 13 is provided, and the portion serves as a ground contact end. The inside of the ellipse drawn with a solid line shows the ground contact surface under the front wheel mounting condition.

  The pneumatic tire of the present invention is a type in which the mounting direction is specified, but may be a tire in which the rotation direction is specified at the same time depending on the shape of the tread pattern.

[Other Embodiments]
(1) In the above-described embodiment, the example in which the outer end portion of the belt reinforcing layer when the vehicle is mounted has a two-layer structure is shown. However, in the present invention, the inner end It is only necessary to provide a belt reinforcing layer having a higher rigidity than the belt portion, and the outer end portion of the belt reinforcing layer when the vehicle is mounted may have a structure of three or more layers, or the cord of the outer end portion of the belt reinforcing layer may be A structure in which the number of drivings is increased, a structure in which the elastic modulus of the cord at the outer end of the belt reinforcing layer is increased, a structure in which the thickness of the cord at the outer end of the belt reinforcing layer (number of filaments and twisted yarns) is increased, A structure combining these may also be used.

  When increasing the number of driving of the cord at the outer end, the number of driving is preferably 24 to 38 / inch.

  (2) In the above-described embodiment, an example in which the outer shoulder is formed as a round shoulder has been shown. However, in the present invention, as shown in FIG. It is preferable that the shoulder is a stepped shoulder having the non-ground portion 23 on the outside. In that case, for example, the vicinity of the boundary between the stepped portion 20 and the tread surface 1c may be a square shoulder.

  The stepped portion 20 of the stepped shoulder 1b is formed with a flat surface or a curved surface, for example. The radius of curvature of the corner when forming with a square shoulder is preferably 1.5 to 10 mm. Further, the radius of curvature near the boundary between the stepped portion 20 and the non-grounding portion 23 is preferably 5 to 20 mm. The inclination angle of the stepped portion 20 is preferably 10 to 60 ° with respect to the normal direction of the axle.

  In the present invention, the boundary 21 between the stepped portion 20 and the tread surface 1c is a distance from the tread center C with the tire maximum width W as a reference, and the distance D1 to the ground shoulder TEi on the round shoulder side in the front wheel mounting condition is 93. It is preferably arranged at a distance D2 of ~ 110%. The distance D1 to the boundary 21 is preferably 95 to 105%, more preferably 95 to 100%. If the distance D1 to the boundary 21 is less than 93%, the ground contact area in normal driving tends to be small, and the braking performance tends to decrease. If the distance D1 to the boundary 21 exceeds 110%, the ground contact during cornering The area reduction effect is reduced, and it is difficult to improve the anti-overturning performance of the vehicle.

  (3) In the above-described embodiment, the example of the tread pattern shown in FIG. 3 is shown. However, when a shoulder with a step is formed as in (2) above, for example, a land portion in which a plurality of inclined grooves 13 are formed. The step portion 20 is formed along the tire circumferential direction PD, and the outer side thereof becomes the non-grounding portion 23. The land portion on which the stepped portion 20 is formed is not limited to such a land portion, and may be any block row, rib, lug, or the like. Further, the stepped portion may be provided at a position where the distance D2 from the center of the tread is different. For example, the distance D2 of the stepped portion can be changed for each block. Even in such a case, it is preferable that any or all of the stepped portions are arranged as a distance from the center of the tread at a distance of 93 to 110% of the distance to the grounding end on the round shoulder side in the front wheel mounting condition.

  (4) In the above-described embodiment, an example in which the tread portion is not divided into the inner side and the outer side is shown. However, as shown in FIG. 4, the tread rubber 9 of the tread portion 1 may be divided into at least two. In that case, it is preferable that the loss tangent (tan δ) of the inner tread rubber 9a disposed on the innermost side when the vehicle is mounted is larger than the loss tangent (tan δ) of the outer tread rubber 9b disposed on the outermost side when the vehicle is mounted. .

  More preferably, the loss tangent of the inner tread rubber 9a is 0.30 to 0.40, particularly 0.35 to 0.40, and the loss tangent of the outer tread rubber 9b is 0.10 to 0.20. This is the case of 0.10 to 0.15. If the loss tangent of the inner tread rubber 9a is less than 0.25, the μ value of the entire tread tends to be low and it tends to be difficult to maintain the braking performance, and if it exceeds 0.45, the μ value becomes too high. There is a tendency that improvement in capsize prevention performance is not observed. Further, if the loss tangent of the outer tread rubber 9b is less than 0.09, the μ value tends to be too low and the braking performance tends to deteriorate, and if it exceeds 0.25, the μ value increases and the gripping force is reduced. There is a tendency that the effect of preventing the overturn of the vehicle due to the decrease is reduced.

  As described above, when obtaining a loss tangent larger than that of the conventional tread rubber, the type of rubber having a large loss tangent (for example, NR or IR) is selected, the amount of plasticizer is increased, or carbon black particles. What is necessary is just to make a diameter small. Conversely, when obtaining a rubber having a smaller loss tangent than the conventional tread rubber, the type of rubber having a smaller loss tangent (for example, BR or SBR) is selected, the amount of plasticizer is reduced, or the carbon black particle size is reduced. Just make it bigger.

  The μ value of the tread rubber 9 can also be changed depending on the hardness of the rubber, and the μ value increases as the JISA hardness increases. For this reason, for the same reason as in the case of the loss tangent, in the present invention, the JISA hardness of the inner tread rubber 9a is preferably larger than the JISA hardness of the outer tread rubber 9b. More preferably, the inner tread rubber 9a has a JISA hardness of 60 to 75 °, and the outer tread rubber 9b has a JISA hardness of 50 to 60 °.

  In the present invention, the division position 9c of the tread rubber 9 on the tread surface is 20 mm inside the boundary 21 between the stepped portion 20 and the tread surface 1c from a position 5 mm outside the tread center C with respect to the tire maximum width W. It is preferable to arrange within the range of the position. More preferably, it is a case where it is arranged within a range of a position of 10 mm outside the center C of the tread and a position of 30 mm inside the boundary 21 between the stepped portion 20 and the tread surface 1c. If the divided position 9c is arranged outside the center of the tread C and inside the position of 5 mm, the μ value of the entire tread tends to be low and it becomes difficult to maintain the braking performance. If it is arranged outside the position, the effect of preventing the vehicle from overturning due to a decrease in grip force tends to be reduced.

  The division position 9c may be arranged in the groove or may be arranged on the land surface. Further, the division boundary surface of the tread rubber 9 may be inclined or perpendicular to the axle direction.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

(1) Loss tangent (tan δ)
Using a spectrometer tester manufactured by Iwamoto Seisakusho, measurement was performed under the conditions of initial elongation of 10%, dynamic strain of 2%, temperature of 60 ° C., and frequency of 10 Hz. A test strip having a strip shape of 5 mm width × 1 mm thickness was prepared, and the grip length was 20 mm.

(2) JISA hardness The hardness by the durometer hardness test (type A) of JISK6253 was measured.

(3) Braking distance After assembling a prototype tire to be described later to the rim (7-JJ-17), filling it with an internal pressure of 230 kPa and mounting it on an actual vehicle (domestic station wagon), the dry road surface under the load conditions of two passengers After running and running at a speed of 100 km / h, braking was applied and the braking distance was measured. The braking performance was evaluated by an index with the braking distance of the conventional product as 100. The larger the index, the better the braking performance.

(4) Maximum cornering force (CFmax)
After assembling a prototype tire to be described later on the rim (7-JJ-17), filling the inner pressure with 230 kPa, and gradually increasing the snake angle at a test speed of 80 km / h using a flat belt cornering tester. The value when the cornering force was maximized was defined as CFmax. At that time, the load conditions were a load 4550N for the front wheel mounting condition and a load 2550N for the rear wheel mounting condition. CFmax was evaluated as an index with the value of the conventional product as 100. The smaller the index, the better the vehicle rollover prevention performance.

Conventional product In the cross-sectional view shown in FIG. 1, the inner round shoulder (drop amount Di = 8 mm, shoulder radius of curvature 30 mm) is also adopted on the outer side, with a tread rubber having a loss tangent of 0.21 and a JISA hardness of 63, Trial tires of size 215 / 55R17 were produced with the pattern shown in FIG. At that time, the belt reinforcing layer was provided so as to cover the entire belt by using a ply of 18 driven / inch of nylon fibers (940 dtex / 2). The results of evaluation using this prototype tire are shown in Table 1.

Example 1
In the sectional view shown in FIG. 1, an inner round shoulder (drop amount Di = 8 mm, shoulder radius of curvature 30 mm) and an outer round shoulder (drop amount Do = 11 mm, shoulder radius of curvature 30 mm) are employed. Trial tires of size 215 / 55R17 were produced with tread rubber having a loss tangent of 0.21 and a JISA hardness of 63 in the pattern shown in FIG. 3, and the above performance was evaluated. At that time, the belt reinforcing layer is formed by using a ply of 18 fibers / inch driven by nylon fibers (940 dtex / 2), and using the same ply, the distance D1 from the center of the tread is 100 to 120% of the distance D1. The upper layer (one layer) was formed in the region of the distance range, and the lower layer was provided so as to cover the entire belt. The results are shown in Table 1.

Example 2
In Example 1, except that the upper layer of the belt reinforcing layer has a two-layer structure, a prototype tire was produced under exactly the same conditions, and the above performance was evaluated. The results are shown in Table 1.

Example 3
In Example 1, the prototype tire was manufactured under exactly the same conditions except that the upper layer of the belt reinforcing layer was not provided and the number of shots was set to 34 / inch only on the outer side of the lower layer (the region where the upper layer was provided in Example 1). It produced and evaluated the said performance. The results are shown in Table 1.

Example 4
In Example 1, the prototype tire was manufactured under exactly the same conditions except that the upper layer of the belt reinforcing layer was not provided and the cord was thickened only on the outer side of the lower layer (the region where the upper layer was provided in Example 1) (1260 dtex / 2). It produced and evaluated the said performance. The results are shown in Table 1.

Example 5
In Example 1, instead of providing an outer round shoulder, a prototype tire was produced under exactly the same conditions except that a shoulder with a step (drop amount Do = 11 mm) shown in FIG. 4 was provided, and the above performance was evaluated. . The results are shown in Table 1. The shoulder with shoulders is a square shoulder (with a radius of curvature of 2 mm) formed at a position where the boundary position with the tread surface is D1-10 mm (95% of D1), and the outside is a non-grounding part. It is.

Comparative Example 1
In Example 1, the inner round shoulder was also adopted on the outer side (drop amount Do = Di), and a prototype tire was produced under exactly the same conditions except that the upper layer of the belt reinforcing layer was coated on the entire lower layer. Evaluated. The results are shown in Table 2.

Comparative Example 2
In Example 1, the inner round shoulder was also adopted on the outer side (drop amount Do = Di), and the prototype tire was produced under exactly the same conditions except that the upper layer of the belt reinforcing layer was covered with the entire lower layer with a two-layer structure. The above performance was evaluated. The results are shown in Table 2.

Comparative Example 3
In Example 1, the inner round shoulder is also adopted on the outer side (drop amount Do = Di), and the upper layer of the belt reinforcing layer is not provided, and the number of driving of the entire lower layer is set to 34 / inch. Prototype tires were produced under the same conditions, and the above performance was evaluated. The results are shown in Table 2.

Comparative Example 4
In Example 1, the inner round shoulder is also adopted on the outer side (drop amount Do = Di), and the upper layer of the belt reinforcing layer is not provided, and the entire lower layer is thickened (1260 dtex / 2). Prototype tires were produced under the same conditions, and the above performance was evaluated. The results are shown in Table 2.

Comparative Example 5
In Example 1, except that the inner round shoulder was also adopted on the outer side (drop amount Do = Di), prototype tires were produced under exactly the same conditions, and the above performance was evaluated. The results are shown in Table 2.

Comparative Example 6
In Example 1, except that the upper layer of the belt reinforcing layer was not provided but only the lower layer was provided (the same belt reinforcing layer as that of the conventional product), a prototype tire was produced under exactly the same conditions, and the above performance was evaluated. The results are shown in Table 2.

  As shown in the results of Table 1, in the pneumatic tire according to the example of the present invention, the front wheel load CFmax was reduced while maintaining the braking performance, and the rollover prevention performance of the vehicle was improved. On the other hand, as shown by the results in Table 2, in Comparative Examples 1 to 4 in which the round shoulder and the belt reinforcing layer are bilaterally symmetrical, the braking performance was lowered and the effect of reducing the front wheel load CFmax was small. Further, in Comparative Example 5 in which the round shoulder is symmetrical and the belt reinforcement layer is asymmetric, the effect of reducing the front wheel load CFmax is not observed, and in Comparative Example 6 in which the round shoulder is asymmetric and the belt reinforcement layer is symmetrical, the front wheel load CFmax is also obtained. No reduction effect was observed.

A meridian cross-sectional view showing an example of the pneumatic tire of the present invention Explanatory drawing for demonstrating the effect of the pneumatic tire of this invention The top view which shows an example of the tread pattern of the pneumatic tire of this invention The meridian cross-sectional view showing another example of the pneumatic tire of the present invention

Explanation of symbols

1 tread part 1a inner shoulder 1b outer shoulder (stepped shoulder)
DESCRIPTION OF SYMBOLS 1c Tread surface 2 Side wall part 3 Bead part 9 Tread rubber 9a Inner tread rubber 9b Outer tread rubber 9c Division | segmentation position 20 Step part 21 The boundary of a step part and a tread surface 23 Non-grounding part 24 Belt reinforcement layer D1 Grounding end of a round shoulder side Distance to D2 Distance to step boundary Di Drop amount (inside)
Do drop amount (outside)
TEi Round shoulder side grounding edge T Tread pattern PD Tire circumferential direction C Tread center W Tire maximum width

Claims (4)

A pair of bead portions, a sidewall portion extending outward in the tire radial direction from each bead portion, a tread portion provided between the sidewall portions, and a belt layer disposed below the tread portion are provided and mounted. For pneumatic tires whose direction is specified,
When the distance from the center of the tread based on the maximum tire width to the inner ground contact end when the vehicle is mounted under the front wheel mounting condition is D1, and the drop amount in the no-load state at the inner shoulder distance D1 is Di,
On the outside of the tread portion when the vehicle is mounted, an outer shoulder is formed in which a drop amount Do in a no-load state at a distance D1 from the center of the tread is larger than Di,
A pneumatic tire characterized in that a belt reinforcing layer having higher rigidity than that of the inner end portion is provided on the outer end portion of the belt layer when the vehicle is mounted.   2. The pneumatic tire according to claim 1, wherein the inner shoulder is a round shoulder, and the outer shoulder is a stepped shoulder having a step portion so that the outer side of the step portion is a non-grounding portion.   The pneumatic tire according to claim 2, wherein a boundary between the step portion and the tread surface is disposed at a distance of 93 to 110% of a distance D1 from the center of the tread.   The pneumatic tire according to claim 2 or 3, wherein a vicinity of a boundary between the step portion and the tread surface is formed by a square shoulder.

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