JP2014136562A - Tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a run-flat tire whose rolling resistance performance in normal running is improved and in addition, whose wet brake performance is improved.SOLUTION: A tire is formed by disposing a pair of side walls and a tread along a carcass striding over a pair of beads in a toroidal shape. The tire includes: a reinforcement rubber layer having a crescent-shaped cross section on the side walls; and a belt formed of at least one belt layer on an outside in a radial direction of the carcass of the tread, respectively. The tread has a center tread rubber disposed on a tread width direction central area including a tire equator, and shoulder tread rubbers disposed adjacently to both sides of the center tread rubber. Elastic modulus and tan δ of the center tread rubber are greater than those of the shoulder tread rubbers, and an end of the center tread rubber is positioned in a range of 30-60% of a half width of the maximum width belt layer of the belt from the tire equator.

Description

  The present invention relates to a side-reinforced run-flat tire having improved wet braking performance in addition to rolling resistance performance in normal running.

  Conventionally, a so-called side-reinforcement type run-flat tire in which a side reinforcing rubber layer having a crescent-shaped cross section is provided on a sidewall portion of the tire as a tire that can travel a certain distance even when the tire internal pressure is reduced by puncture or the like. is there. This run-flat tire supports the load with the tire internal pressure during normal running, and supports the tire load as a shoulder with a side reinforcing rubber layer during puncturing. For this reason, even if the air pressure inside the tire suddenly drops during tire puncture, there is no sudden change in the behavior of the vehicle, so stable driving is possible, and there is a risk of accidental steering operation by a driver Can be reduced.

On the other hand, in this side-reinforced run-flat tire, the high-rigidity sidewall that hardly undergoes bending deformation under load pushes the shoulder area of the tread, so the direction of the tire equator from both shoulder areas of the tread A compressive force is generated, and the center region of the tread portion is easily deformed so as to be curved in an arc shape inward in the tire radial direction. Along with this deformation, the contact pressure in the shoulder region is extremely increased and the heat generation amount is increased, so that the rolling resistance tends to increase as compared with a normal tire having no side reinforcing rubber layer.
Therefore, in Patent Document 1, a low heat-generating rubber is disposed in the tread portion, and at the same time, the ground pressure in the shoulder region of the tread portion is reduced by using rubber having an appropriate storage elastic modulus for the side reinforcing rubber layer. Therefore, a tire is disclosed in which the bending deformation of the tread portion is suppressed and the rolling resistance performance and the uneven wear resistance performance are improved.

JP 2010-221914 A

According to the configuration of Patent Document 1, the rolling resistance of the tire can be reduced as compared with the conventional tire, while the low heat-generating rubber is a normal rubber with a small content of carbon, additives, and the like. Therefore, when such a low heat-generating rubber is applied to the entire tread portion, it is inevitable that the rigidity of the tread becomes smaller than that of the conventional tread portion and is disadvantageous for the wet braking performance. On the other hand, there is an increasing demand for improving the wet braking performance together with the rolling resistance performance.
Accordingly, an object of the present invention is to provide a side-reinforced run-flat tire having improved wet braking performance in addition to rolling resistance performance.

  The inventors diligently investigated the means for solving the above-mentioned problems.In the side-reinforced run-flat tire, the shoulder region of the tread portion that receives the tire load from the highly rigid sidewall portion, and the shoulder region By individually defining the physical properties of the rubber that is sandwiched and compressed and arranged in the same center region that tends to bend in an arcuate shape inside the tire in the radial direction, curving deformation of the tread part is suppressed and rolling resistance performance is improved. In addition, the inventors have newly found that the wet braking performance can be improved, and have completed the present invention.

The gist of the present invention is as follows.
(1) The tire according to the present invention includes a pair of sidewall portions and a tread portion arranged along a toroidal shape between a pair of bead portions, and a reinforcing rubber having a crescent cross section in the sidewall portion. Each of the tires includes a belt formed of at least one belt layer on the outer side of the tread portion in the radial direction of the carcass, and the tread portion is disposed in a center region in the tread width direction including the tire equator. A center tread rubber, and a shoulder tread rubber adjacent to both sides of the center tread rubber. Both the elastic modulus and tan δ of the center tread rubber exceed those of the shoulder tread rubber, and the end of the center tread rubber The portion corresponding to 30% to 60% of the half width of the maximum width belt layer of the belt from the tire equator It is located, characterized by.

  (2) The tire of the present invention has a plurality of circumferential grooves in the tread, and the end portion of the center tread rubber is a groove bottom edge on the tread end side of the outermost circumferential groove in the tire width direction or It is preferable to be positioned on the outer side in the tire width direction from the groove bottom edge.

  (3) In the tire of the present invention, it is preferable that the interface between the center tread rubber and the shoulder tread rubber is located between one opening edge and the other opening edge of the circumferential groove. is there.

  (4) In the tire of the present invention, it is preferable that the ratio Ec / Es of the elastic modulus Ec of the center tread rubber to the elastic modulus Es of the shoulder tread rubber is 4.5 or less.

  (5) In the tire of the present invention, it is preferable that the position of the end portion of the center tread rubber is different between one side and the other side of both sides sandwiching the tire equator.

  (6) In the tire of the present invention, it is preferable that the shoulder tread rubber has different elastic modulus and tan δ on one side and the other side of the center tread rubber.

  The elastic moduli Ec and Es are measured under the conditions of an initial strain of 0.2%, an amplitude of 1%, a frequency of 52 Hz, and a temperature of 25 ° C. according to JIS K6394.

  According to the present invention, since the rigidity of the tread portion can be suitably increased, it is possible to provide a run-flat tire with improved wet braking performance in addition to rolling resistance performance in normal running.

It is a figure which shows the half part of the cross section of the width direction of the tire which concerns on embodiment of this invention. It is an enlarged view of the circumferential groove | channel of the tire width direction outermost side shown in FIG. It is a figure which shows the half part of the cross section of the width direction of the tire which concerns on other embodiment of this invention. It is a figure which shows the half part of the cross section of the width direction of the tire which concerns on other embodiment of this invention. (A) is sectional drawing of the tire width direction at the time of normal driving | running | working of the tire which concerns on this invention, (b) is the same sectional drawing of a conventional example tire.

Hereinafter, the tire of the present invention will be described in detail by exemplifying an embodiment thereof with reference to the drawings.
In FIG. 1, the half part of the cross section of the width direction of the tire which concerns on this invention is shown. In the tire of the present invention, a pair of sidewall portions 12 and a tread portion 13 are disposed along a toroidal shape between a pair of bead portions 11, and the sidewall portion 12 has a crescent-shaped cross section. The tire is a so-called run-flat tire including the reinforcing rubber layer 5 and the belt 3 including at least one (two layers in the drawing) belt layers 3a and 3b on the outer side in the radial direction of the carcass 2 of the tread portion 13. . The tread portion 13 includes a center region C disposed in the center region in the tread width direction including the tire equator CL, and a shoulder region S extending adjacent to both sides of the center region C. The center region C includes a center tread. The rubber TC and the shoulder tread rubber TS are disposed in the shoulder region S, respectively.

Here, it is important that both the elastic moduli Ec and tan δ of the center tread rubber TC exceed the elastic moduli Es and tan δ of the shoulder tread rubber TS.
As shown in FIG. 5 (b), in the conventional side-reinforced run-flat tire, the sidewall portion 12 'has high rigidity and does not bend and deform when loaded, so the sidewall portion 12' is the shoulder of the tread portion 13 '. Since the region is pushed in, a compressive force is generated in the direction of the tire equator CL from both shoulder regions of the tread portion 13 ′, and the center region of the tread portion 13 ′ is deformed to be curved inward in the tire radial direction. For this reason, while the ground contact pressure in the shoulder region is extremely increased, the ground contact surface in the center region is small and the load sharing ratio is small.

  Therefore, the elastic modulus Ec of the center tread rubber TC is made larger than the elastic modulus Es of the shoulder tread rubber TS, and the center tread rubber TC curves inward in the tire radial direction even when subjected to compression from the adjacent shoulder tread rubber TS. If not, the tire load can be borne not only in the shoulder area S of the tread 6 but also in the center area C as shown in FIG. An increase in rolling resistance in the region S can be suppressed.

At this time, the wet braking performance of the tire can be improved by relatively increasing the tan δ of the center tread rubber TC disposed in the center region C. In general, rubber with a large tan δ generates a large amount of heat and may impair the rolling resistance performance of the tire. However, as described above, in the side-reinforced run-flat tire, the ground pressure in the center region C of the tread portion 13 Is not so high as compared with the shoulder region S, and even when rubber having a large tan δ is disposed in the center region C, the wet braking performance can be improved without impairing the rolling resistance of the tire.
On the other hand, the amount of heat generated in the shoulder region S can be reduced by disposing rubber with a relatively small tan δ, which generates low heat, in the shoulder region S where the contact pressure tends to concentrate.
Moreover, by suppressing the curved deformation of the tread portion 13, it is possible to suppress uneven wear of the tread and to improve the steering stability performance.

Furthermore, as shown in FIG. 1, it is necessary to arrange the end portion E _TC of the center tread rubber TC in a range corresponding to 30% to 60% of the half width HW of the maximum width belt layer 3a of the belt 3 from the tire equator CL. is there.
If it is 30% or more, the arrangement area of the center tread rubber TC having a relatively high elastic modulus in the tread 6 can be sufficiently secured, and the bending deformation of the tread portion 13 can be suppressed. Further, if it is 60% or less, the center tread rubber TC increases the rigidity of the center region C of the tread portion 13 and also sufficiently secures the arrangement area of the shoulder tread rubber having relatively low heat generation, thereby increasing the rolling resistance. Can be suppressed.
Incidentally, the end portions E _TC of the center tread rubber TC, from the tire equator CL, be arranged in a range more than 60% of the half width HW of the widest belt layer 3a of the belt 3, to suppress the bending deformation of the tread portion 13 Since the effect is saturated, it is set to 60% or less.
More preferably, the end portion E _TC of the center tread rubber TC is arranged in a region from 50% to 60% of the half width HW of the maximum width belt layer 3a of the belt 3 from the tire equator CL.

  At this time, the elastic modulus Ec of the center tread rubber TC and the elastic modulus Es of the shoulder tread rubber TS are preferably 3 MPa or more and 21 MPa or less. If it is 3 MPa or more, the rigidity of the tread 6 can be sufficiently secured to maintain good wear performance, and if it is 21 MPa or less, riding comfort performance can be maintained.

Further, the run flat tire 10 according to the present invention has a plurality of circumferential grooves 1 in the tread 6, and as shown in FIG. 2, the end portion E _TC of the center tread rubber TC is at the outermost side in the tire width direction. circumferential direction groove 1 is preferably located outward in the tire width direction than the groove bottom edges d ₁ or the groove bottom d ₁ of the tread end side.

  In general, the tread portion 13 in the side-reinforced run-flat tire is curved by bending the tread in the circumferential groove 1 having a smaller rigidity than the land portion 7 of the tread. In particular, the outermost circumferential groove 1 in the tire width direction is most susceptible to being pushed from the sidewall portion 13, so that the center tread rubber having a relatively high rigidity is provided at least in the groove bottom d of the outermost circumferential groove 1. By disposing TC, it is difficult to bend the circumferential groove 1 when a load is applied, and curving deformation of the tread portion 13 can be suppressed. Therefore, it is possible to obtain an effect of reducing rolling resistance and particularly suppressing uneven wear of the tread.

Unlike the circumferential groove 1 in which the groove bottom d is flat as shown in FIG. 2, the circumferential groove in which the groove bottom d has an arc shape that protrudes inward in the tire radial direction has two groove walls. , the respective inflection points in the tire radial direction outermost and Mizosokoen d ₁ and Mizosokoen d _2. With respect to the circumferential groove of the other shape, the deepest point of the groove and Mizosokoen d _1.

Here, the interface P between the center tread rubber TC and the shoulder tread rubber TS is preferably located between _one opening edge e ₁ and the other opening edge e ₂ of the circumferential groove 1.

  This is because, when the interface P is arranged on the land portion 7 of the tread 6, when the tread 6 is grounded, a rigidity step is generated between the center tread rubber TC and the shoulder tread rubber TS having different elastic modulus and tan δ. This is because the tread 6 is likely to be unevenly worn and the rolling resistance increases. Therefore, if the interface P is arranged within the range of the circumferential groove 1 that does not come into contact with the road surface, the influence of the rigid step as described above can be kept small, and the uneven wear resistance and rolling resistance performance can be further improved. .

  Furthermore, the ratio Ec / Es of the elastic modulus Ec of the center tread rubber TC to the elastic modulus Es of the shoulder tread rubber TS is preferably 4.5 or less.

The ratio Ec / Es is set to 4.5 or less because when the ratio exceeds 4.5, the rigidity step between the center tread rubber TC and the shoulder tread rubber TS becomes large. This is because the contact pressure difference between the center region C and the shoulder region S becomes too large, and in particular, slipping occurs on the contact surface of the shoulder region S and the shoulder region S is easily worn.
In addition, it is further more preferable that said ratio Ec / Es is 1.5 or more and 4.0 or less from a viewpoint of suppressing suitably the rigid level | step difference between both rubber | gum.

  The ratio of tan δ of the center tread rubber TC to tan δ of the shoulder tread rubber TS is preferably 2.0 or more and 3.5 or less from the viewpoint of wet braking performance. More preferably, this ratio is 2.5 or more and 3.0 or less.

Further, the position of the end portion E _TC of the center tread rubber TC may be different between one side and the other side of the both sides of the tire equator CL.
In general, compared to the inner side of the tire when the vehicle is mounted, the outer side has a greater pushing force from the sidewall portion, so the center tread rubber TC having a relatively high rigidity has a larger tire width direction length. If it is used so as to be on the outer side when the tire is mounted, the curved deformation of the tread portion 13 is more effectively suppressed, so that the uneven wear resistance performance and the rolling resistance performance can be further improved.

Further, the elastic moduli Es and tan δ of the shoulder tread rubber TS may be different between one tire half and the other tire half.
In general traveling, the stress on turning is relatively large on the outer side of the tire when the vehicle is mounted, while the ground contact pressure of the tread when traveling straight is relatively large on the inner side, so that the elastic modulus Es of the shoulder tread rubber TS is If the higher and larger tan δ are used so as to be on the outer side when the tire is mounted, uneven wear can be suppressed on the outer side of the tire, and rolling resistance can be more efficiently reduced on the inner side.

Examples of the present invention will be described below.
Invention example tires, comparative example tires and conventional example tires (both tire sizes are 225 / 45R17) were prototyped under the specifications shown in Tables 1 to 3 and evaluated for rolling resistance performance, wet braking performance and uneven wear resistance performance. .
Each test tire includes a pair of sidewall portions and a tread portion disposed along a toroidal shape between a pair of bead portions, and a crescent-shaped reinforcing rubber layer in the sidewall portion, and The tire includes a belt composed of at least one belt layer on the outer side of the tread portion in the radial direction of the carcass.

The conventional tires 1 and 2 in Table 1 are tires in which the tread is made of a single rubber as shown in FIG. 5B, and the inventive tires 1 to 5 and the comparative example tires 1 to 3 are treads. The tire is composed of a center tread rubber TC disposed in the center region in the tire width direction including the tire equator, and a shoulder tread rubber TS adjacent to both sides of the center tread rubber.
The invention example tire 6 in Table 2 is a tire in which the end portion E _TC of the center tread rubber TC is located near the center of the groove bottom d. Example tire 7, as shown in FIG. 1, a tire positioned on the end portion E _TC exactly Mizosokoen d ₁ of the center tread rubber TC, Example tire 8, as shown in FIG. 3, end E _TC of the center tread rubber TC is located in 5.0mm tire width direction outer side than Mizosokoen d _1, and the interface P of the center tread rubber TC and the shoulder tread rubber TS is a tire in the tread surface position . In addition, as shown in FIG. 4, the example tires 9 and 10 have the end portion E _TC of the center tread rubber TC located 5.0 mm or 6.0 mm outside the groove bottom edge d _{1 in the} tire width direction, This is a tire in which the interface P is not located at the tread surface.
Inventive tires 11 to 13 in Table 3 differ in the position of the end portion E _TC of the center tread rubber TC between one side and the other side of the tire equator, and the shoulder tread rubber TS is the center tread rubber TC. Is a tire having different elastic modulus and tan δ on one side and the other side. In various tests of the following Example tire 12, the position of the end portion E _TC of the center tread rubber TC is a person who is outside the tire width direction, were used in the outside when the tire is mounted. Inventive Example Tire 13 was used with the shoulder tread rubber TS having a higher elastic modulus and a larger tan δ facing outside when the tire was mounted.

(Rolling resistance performance)
Each test tire was assembled to the rim 7.5J17, and after applying an internal pressure of 210 kPa, the rolling resistance of the axle was determined using a drum testing machine (speed: 80 km / h) having a steel plate surface with a diameter of 1.7 m. . The rolling resistance was measured according to ISO18164, using a smooth drum and force type.
The results are shown as an index in Table 1 where the rolling resistance of the conventional tire 1 is 100 and the rolling resistance of the conventional tire 3 is 100 in Table 3. The smaller the index, the better the performance.

(Wet braking performance)
Each test tire was assembled on a rim 7.5J17, and after applying an internal pressure of 230 kPa, it was mounted on an actual vehicle (4 passengers) and fully braked at a speed of 40 km / h on a wet asphalt road test course with a water depth of 10 mm. When braking distance was measured. The results are shown as indices in Table 1 with the braking performance of the conventional tire 1 as 100 and the braking performance of the conventional tire 3 as 100 in Table 3. The larger the index, the better the performance.

(Uneven wear resistance)
Each test tire was assembled to the rim 7.5J17, and after applying an internal pressure of 230 kPa, it was mounted on a real vehicle (4 passengers) and traveled 10,000 km, and the presence or absence of uneven wear was evaluated from the tire appearance. In Table 2, the index of the invention tire 6 is shown as an index, and in Table 3, the wear resistance performance of the conventional tire 3 is set as 100. The larger the index, the better the performance.

1: Circumferential groove 2: Carcass 3: Belt 3a: Maximum width belt layer 3b: Belt layer 4: Reinforcement layer 5, 5 ': Side reinforcement rubber layer 6: Tread 7: Land portion 11: Bead portion 12, 12': sidewall portions 13 and 13 ': the tread portion d: groove bottom d _{1, d 2:} Mizosokoen e _{1, e 2:} opening edge C: Center area CL: tire equator E _TC center tread rubber end HW: Half width of maximum belt layer S: Shoulder area TC: Center tread rubber TS: Shoulder tread rubber

Claims (6)

A pair of sidewall portions and a tread portion are disposed along a toroidal shape between a pair of bead portions, a crescent-shaped reinforcing rubber layer in the sidewall portion, and the carcass of the tread portion. Tires each including a belt composed of at least one belt layer on the outside in the radial direction,
The tread portion has a center tread rubber disposed in the center region in the tread width direction including the tire equator, and shoulder tread rubber adjacent to both sides of the center tread rubber,
Both the elastic modulus and tan δ of the center tread rubber exceed those of the shoulder tread rubber,
The tire is characterized in that an end portion of the center tread rubber is located in a range from 30% to 60% of a half width of the maximum width belt layer of the belt from the tire equator.   The tread has a plurality of circumferential grooves, and the end of the center tread rubber has a groove bottom edge on the tread end side of the circumferential groove on the outermost side in the tire width direction or the tire width direction from the groove bottom edge. The tire according to claim 1, which is located outside.   The tire according to claim 1, wherein an interface between the center tread rubber and the shoulder tread rubber is located between one opening edge and the other opening edge of the circumferential groove.   The tire according to any one of claims 1 to 3, wherein a ratio Ec / Es of an elastic modulus Ec of the center tread rubber to an elastic modulus Es of the shoulder tread rubber is 4.5 or less.   The tire according to any one of claims 1 to 4, wherein a position of an end portion of the center tread rubber is different between one side and the other side of the both sides of the tire equator.   The tire according to any one of claims 1 to 5, wherein the shoulder tread rubber has different elastic moduli and tan δ on one side and the other side of the center tread rubber.

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