JP5497401B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having excellent uneven wear resistance and low rolling resistance.

In recent years, development of products with a smaller environmental load has been actively conducted. This is due to environmental problems such as global warming, and tires are no exception. With respect to this tire, in order to cope with the environmental problem, it is important to secure performance that contributes to reducing fuel consumption of the automobile. One means for achieving this is to reduce the rolling resistance of the tire, and various technical developments have been made in the past.
The following introduces some conventional improvements.

  First, it is known that a large amount of tire rolling resistance occurs in the rubber of the tread portion. As a direct improvement method, it is effective to change the rubber used for the tread portion to one having a small loss tangent. However, it is also known that this method sacrifices other performance of the tire, such as wear resistance. On the other hand, a method of reducing the tread thickness can be easily considered in order to reduce the rubber that is a source of increasing rolling resistance. However, in this case, the problem is that the wear life of the tire cannot be ensured.

  Furthermore, Patent Document 1 proposes reducing the rolling resistance by devising the cross-sectional shape of the tire. This proposal will surely reduce rolling resistance, but the durability of the appearance of the side is not sufficient, and more detailed tire design is required when considering other performance, especially excellent wear resistance. It has been demanded.

JP 2006-327502

  Therefore, an object of the present invention is to propose the details of the tire shape for providing a tire having excellent wear resistance performance and low rolling resistance, and also to ensure the durability of the appearance of the side portion of the new shape. is there.

Inventors are able to improve the expected performance by regulating the shape of the tire in detail, especially in the case of shape design, not only the shape of the outer surface of the tire but also the reinforcement that becomes the skeleton of the tire Since the shape of the structure has a great influence on the tire performance, we have learned that it is effective to regulate it individually. In other words, suppressing the shear deformation in the tire width direction cross section, particularly in the tread on the outer side in the width direction, reduces the rolling resistance as a result of energy loss due to this deformation, and the shear force and slip resulting from this deformation. It has been found that the wear often described can be improved at the same time.
Furthermore, regarding the durability of the appearance of the side portion of the tire, which is often seen in tires with flat belt lines, the wear resistance performance and rolling resistance reduction performance described above are impaired by defining the folding height of the carcass ply. As a result, the present invention has been completed.

The gist of the present invention is as follows.
In addition, regarding the tire dimension mentioned later, please refer FIG. 1 which shows the width direction cross section of a common tire.
(1) A diameter of a crown portion of the carcass having a carcass made of a carcass ply formed between a bead portion embedding a pair of bead cores in a toroidal shape and folded back from the inner side to the outer side in the tire width direction around the bead core. A pneumatic tire in which a belt having at least one inclined belt layer and a tread are sequentially arranged on the outer side in the direction,
The ratio of the diameter difference BD between the widthwise central portion and the widthwise end of the outermost layer to the width BW of the outermost layer of the inclined belt layer in the tire widthwise cross-section when the tire is mounted on the applicable rim. In the pneumatic tire whose BD / BW is 0.01 or more and 0.04 or less,
The shortest distance CSEh between the tip of the folded portion of at least one layer of the carcass ply and the line segment drawn parallel to the tire rotation axis on the bead toe is the line segment drawn parallel to the tire rotation axis at the maximum tire width position. And a bead toe, which is greater than the shortest distance SWh between a line segment drawn parallel to the tire rotation axis.

  Here, the state in which the tire is mounted on the applicable rim is a state in which the tire is incorporated in a standard rim or other applicable rim stipulated in the Japan Automobile Tire Association Standard (JATMA), without applying internal pressure, or about 30 kPa. This means a state with an extremely low internal pressure of up to.

(2) The line segment drawn parallel to the tire rotation axis at the maximum width position of the carcass and the bead toe parallel to the tire rotation axis with respect to the tire radial distance CSH between the outermost radial direction of the carcass and the bead toe The pneumatic tire according to (1) above, wherein a ratio CSWh / CSH of the shortest distance CSWh to the line segment drawn in is 0.6 to 0.9.

(3) The pneumatic tire as described in (1) or (2) above, wherein a ratio SWh / SH of the shortest distance SWh to a sectional height SH of the tire is 0.5 or more and 0.8 or less. .
(4) The pneumatic tire according to any one of (1) to (3), wherein the ratio CSEh / SWh is 1.02 or more and 1.25 or less.

It is a figure which shows the width direction cross section of a common tire. It is a figure which shows the cross section of the width direction of the tire of this invention. It is a figure which shows the behavior before and behind the load load of the conventional tire. It is a figure which shows the behavior before and behind the load load of the tire of this invention. It is a figure for demonstrating the tensile distortion at the time of changing the neutral axis | shaft of bending. It is a figure which shows the cross section of the width direction of the tire of this invention. It is a figure which shows the cross section of the width direction of the tire of this invention. It is a figure which shows the width direction cross section of the conventional tire.

Hereinafter, the present invention will be specifically described with reference to the drawings.
FIG. 2 shows a cross section in the width direction of the pneumatic tire of the present invention (hereinafter referred to as a tire). The tire 6 of the present invention has a toroidal shape between the bead portions in which the pair of bead cores 1 are embedded, and at least one layer that is folded around the bead core 1 from the inner side to the outer side in the tire width direction. At least one layer in which a carcass 2 made of ply is used as a skeleton, and a large number of cords extending in a direction inclined with respect to the equator plane CL of the tire are coated with rubber on the radially outer side of the crown portion of the carcass 2, illustrated example Then, two inclined belt layers 3a and 3b are arranged, and one circumferential belt layer 4 in which a large number of cords extending along the equatorial plane CL of the tire are covered with rubber on the radially outer side thereof is arranged. A tread 5 is disposed outside the belt in the radial direction.
The inclined belt layer may be a single layer, but in that case, it is preferable that the belt is constituted by a combination with at least one circumferential belt layer.

Such a tire 6 is mounted on the application rim 7 and used. Here, in the cross section in the tire width direction in a state where the tire 6 is mounted on the application rim 7, the width direction central portion (equatorial plane CL) of the outermost layer 3b with respect to the width BW of the outermost layer 3b of the inclined belt layer. And the ratio BD / BW of the diameter difference BD between the width direction end portions is 0.01 or more and 0.04 or less.
The inclined belt layer referred to here has a width of 0.6 times or more the maximum width CSW of the carcass 2.

This definition means that the inclined belt layer 3 has a small diameter difference in the width direction. That is, it shows that the belt is almost flat.
As described above, the rolling resistance is dominated by the energy loss generated in the rubber of the tire tread part, and suppressing shear deformation in the cross section in the width direction, which is one of the deformations, reduces rolling resistance. It is valid. This shear deformation is shown in FIG. 3 in a solid line in a radial tire (ratio BD / BW: 0.052) having a normal sectional shape of size 195/65 R15 before filling with an internal pressure of 210 kPa. As indicated by a dotted line later, a state in which a load of 4.41 kN is applied is caused by deformation in which the belt bent at the ground contact portion is stretched flat by deformation before and after the load application (see arrows). Further, as shown in FIG. 3, in a normal radial tire, since the radius of the shoulder relative to the tire center is small and has a diameter difference, the belt near the shoulder is extended in the tire circumferential direction. Then, since the inclined belt layer arranged with the cords crossing is deformed into a pantograph shape and stretches in the circumferential direction, it shrinks in the width direction. This will increase the hysteresis loss.

  In order to suppress this deformation most simply from the shape of the tire, it is necessary to make the belt as flat as possible. That is, for a tire of the same size as the tire of FIG. 3 with a flat belt (ratio BD / BW: 0.026), the deformation before and after loading under the same conditions as in FIG. 3 is shown in FIG. As shown, when the ratio BD / BW is set to 0.04 or less, deformation (see arrows) before and after the load can be suppressed to an extremely small level. Therefore, by setting the ratio BD / BW to 0.04 or less, the hysteresis loss of the tread rubber is reduced, and a tire having a low rolling resistance can be obtained.

  In addition, from the viewpoint of the tread shape, when the above-described improvement for suppressing shear deformation is performed, the shearing force and the slip distribution in the ground plane also change in a direction to be reduced, so that the wear resistance performance can be improved at the same time. Also came to elucidate.

  In actual tire design, it is necessary to consider the deformation component accompanying the deformation of the side part, the ground contact shape to prevent uneven wear, and the contact pressure distribution. It is important to set the range. As a result of diligent research on this appropriate range, it was found that the above-mentioned ratio BD / BW was 0.01 or more.

Further, in FIG. 2, the shortest distance (hereinafter also referred to as the folding height) CSEh between the tip 2OE of the folded portion 2O of the carcass ply and the line drawn to the bead toe 10 in parallel with the rotation axis of the tire is the tire's maximum. It is larger than the shortest distance (hereinafter also referred to as the maximum width / height) SWh between the line segment drawn parallel to the tire rotation axis at the large position W _MAX and the line segment drawn parallel to the tire rotation axis at the bead toe 10. Is essential. Hereinafter, the reason will be described.

As described above, in a tire with a belt that is nearly flat, when the tire bends under load, there is little deflection of the crown portion including the belt, and bending due to deflection tends to concentrate on the side portion. Thereby, the problem on the tire appearance that a crack arises in a side surface layer part has arisen.
In order to suppress cracking of the side surface layer portion, that is, to suppress distortion of the side surface layer portion, it is conceivable to increase the bending rigidity of the side portion so as to suppress the deflection of the side portion. However, as described above, the bending due to the bending is concentrated on the side portion in order to reduce the deformation in the tread portion and reduce the energy loss of the tread portion. It is necessary to reduce the surface strain. The present inventors tried various ways to reduce the side surface distortion while keeping the side part deflection large, and made the folding height CSEh from the bead part of the carcass ply higher than the maximum width height SWh. Thus, it was confirmed that the distortion of the side surface layer portion can be suppressed. At the maximum width position W _MAX of the tire where the bending of the side part is concentrated, the carcass ply folding part is overlapped with the carcass ply body part to double the movement, and the neutral axis of bending at this part moves to the surface layer side. I am letting. As a result, the distortion of the surface layer can be suppressed.

That is, with reference to FIG. 5, a compressive stress acts on the inner side of the bending neutral axis, and a tensile stress acts on the outer side. Rubber has high rigidity against compressive stress but low rigidity against tensile stress. Therefore, as shown in FIG. 5 (a), if the distance d from the neutral axis of the bending to the side surface is large, the tensile strain acting on the outside of the neutral axis of the bending becomes large, so that this portion is likely to crack. . Therefore, as shown in FIG. 5B, if the distance d from the neutral axis of the bending to the side surface is decreased, the tensile strain acting on the outer side of the neutral axis of the bending is reduced, so that it is difficult for cracks to occur in this portion. .
In the present invention, the folding height CSEh from the bead portion of the carcass ply is made higher than the maximum width height SWh, so that the carcass ply is doubled at the maximum width position W _MAX of the tire where the bending of the side portion is concentrated. Thus, the neutral axis of the bending can be moved to the surface layer side, and the distortion of the surface layer of the side portion can be suppressed.
In addition, since only the turn-up height CSEh of the carcass ply is changed, the deflection of the entire tire is not greatly affected.

It is important that the ratio CSEh / SWh of the folded height CSEh to the maximum width height SWh is greater than 1, but preferably 1.02 or more and 2.0 or less. More preferably, it is 1.02 or more and 1.25 or less.
The ratio when CSEh / SWh is 1, i.e., when the tip 2OE of the folded portion 2O of the carcass ply is in the maximum width position _{W MAX,} becomes the tip 2OE of the folded portion 2O in the center of the bend is positioned, the folded portion 2O There is a risk of cracking starting from the tip 2OE. Therefore, it is important that the ratio CSEh / SWh is larger than 1.
The reason why the lower limit of the preferable range of the ratio CSEh / SWh is 1.02 is that the folding height CSEh varies slightly due to manufacturing, and the folding height CSEh always exceeds the maximum width height SWh.
On the other hand, the upper limit of the suitable range of the ratio CSEh / SWh is set to 2.0 because the effect of suppressing surface distortion is not improved even if the folding height CSEh is further increased beyond the maximum width height SWh. is there. Furthermore, in many tires, when this ratio exceeds 2.0, the tip 2OE of the folded portion 2O of the carcass ply has a positional relationship exceeding the belt end. Further, if the folded portion 2O is excessively large, the deflection is also affected, and there is a possibility that the riding comfort is deteriorated due to an increase in the vertical spring.
As will be described later, it is confirmed that the effects of the present invention can be sufficiently obtained when the ratio CSEh / SWh is 1.25.

Next, as shown in FIG. 2, the maximum width position W _CMAX of the main body of the carcass 2 is parallel to the tire rotation axis with respect to the distance CSH in the tire radial direction between the radially outermost side of the carcass 2 and the bead toe 10. It is preferable that the ratio CSWh / CSH of the shortest distance CSWh between the line segment drawn on the bead 10 and the line segment drawn on the bead toe 10 in parallel with the rotation axis of the tire is 0.6 or more and 0.9 or less. More desirably, it is 0.7 or more and 0.8 or less.

  According to this rule, the carcass line of the tire side portion has a region that is locally bent particularly at a position close to the road surface, and the bending rigidity is reduced at this portion. Then, since the periphery of the bent portion, which is on the outer side in the width direction than the belt width, is greatly deformed when loaded, deformation at the tread portion is reduced. That is, the shear deformation in the cross section can be reduced in the tread. As a result of various trials of dimensions for effectively reducing deformation during loading, it was found that the ratio CSWh / CSH was 0.6 or more and 0.9 or less.

  Moreover, as shown in FIG. 2, it is preferable that ratio SWh / SH of the maximum width height SWh with respect to the cross-sectional height SH of a tire is 0.5 or more and 0.8 or less. More preferably, it is 0.6 or more and 0.75 or less.

  Now, it is important to originally define the shape of the side portion with a carcass line that is a skeleton. However, in the phenomenon that energy loss occurs inside the rubber and contributes to rolling resistance, the side portion is no exception. In other words, it can be said that taking the shape of the side portion following the carcass line and different from that of the conventional tire leads to efficient improvement. This means, for example, that the side rubber is thinned. If it is obvious that the side rubber can be eliminated, this dimension indicates the same position as the maximum width of the carcass line. Actually, since it is necessary to give the side rubber a predetermined thickness from the role of protecting the carcass when contacting the curbstone, the maximum width position of the side part at this time is compared with the tire cross section height, It was found to be in the ratio range. Moreover, in the tire design, the design of the vulcanization mold is also an important point, so it is necessary as a tire design method to define it as the outer surface dimension.

Next, another embodiment of the tire of the present invention will be described with reference to FIGS. 6 and 7.
In FIG. 6, the carcass 2 is composed of two layers of carcass plies 2 a and 2 b, and the tip 2 a OE of the folded portion 2 a O of the carcass ply 2 a arranged on the innermost side in the radial direction and the bead toe 10 are drawn parallel to the tire rotation axis. The shortest distance CSEh from the line segment is larger than the maximum width height SWh.
In FIG. 7, the carcass 2 includes two layers of carcass plies 2 a and 2 b, and the turn-up height CSEh of the carcass ply 2 a and the carcass ply 2 b is larger than the maximum width height SWh.
As shown in FIG. 6 and FIG. 7, when the carcass 2 is composed of two layers of carcass plies 2a and 2b, the folding height CSEh of the innermost carcass ply 2a is larger than the maximum width height SWh. At the maximum width position W _MAX , the carcass ply is triple or more, and the neutral axis of bending at this position can be moved to the surface layer side to suppress the distortion of the surface layer of the side portion.

As shown in FIGS. 6 and 7, when the carcass 2 is composed of two layers of carcass plies 2 a and 2 b, the tire radial direction between the outermost radial direction of the carcass ply 2 a of the innermost layer and the bead toe 10 is used. The ratio of the shortest distance CSWh between the line segment drawn parallel to the tire rotation axis and the bead toe 10 parallel to the tire rotation axis to the maximum width position W _CMAX of the carcass ply 2a body relative to the distance CSH CSwh / CSH is preferably 0.6 or more and 0.9 or less.

Conventional tires of the size 195 / 65R15, invention tires and comparative tires were prototyped according to the specifications shown in Table 1, and for each prototype tire, the side wall cracking durability performance, rolling resistance and wear resistance performance The test was conducted and will be described below.
Conventional tires have the tire shape and structure shown in FIG.
The invention example tire and the comparative example tire both have the tire shape and structure shown in FIG. 2, and the height CSEh and the maximum width height SWh of the folded portion of the carcass ply are changed. The thickness from the tire inner surface to the tire outer surface at the tire maximum width position W _MAX is substantially the same.

  The endurance test for the occurrence of cracks in the side part was carried out by mounting each test tire on a standard rim, adjusting the internal pressure to 210 kPa, and then loading conditions 2.5 times the normal load (conditions that promote the occurrence of side cracks) Below, the running distance until a crack generate | occur | produces in the side part was measured using the drum tester (speed: 80.0 km / h) which has an iron plate surface of a diameter of 1.7 m. The measurement results are indexed, indicating that cracks are less likely to occur as the value increases.

In the rolling resistance test, each test tire was mounted on a standard rim, the internal pressure was adjusted to 210 kPa, and then the axle rolling was performed using a drum testing machine (speed: 80 km / h) having a steel plate surface with a diameter of 1.7 m. This was done by determining the resistance. The rolling resistance was measured according to ISO18164, using a smooth drum and force type. The measurement results shown in Table 1 are indexed with the rolling resistance of the conventional tire as 100, and the smaller the value, the lower the rolling resistance.
The longitudinal spring performance is obtained by measuring the amount of deflection during the rolling resistance test and indexing the spring calculated by “load / deflection amount”, and indicates that the greater the value, the less the deflection. That is, it means that the smaller the value is, the more flexible and the ride comfort is. The amount of deflection is determined by the tire shaft height when there is no load minus the shaft height when the load is applied.

In the abrasion resistance test, each test tire was mounted on a standard rim, the internal pressure was adjusted to 210 kPa, and then an indoor drum test having a safety walk on the surface with a diameter of 1.7 m under the same load conditions as the rolling resistance test. Machine (speed: 80 km / h). Input is 10 minutes for free rolling and 0.1G for 10 minutes in the braking direction. Under these conditions, the wear weight (amount of worn rubber) after traveling 1200 km was measured. The measurement results shown in Table 1 are indexed assuming that the wear weight of the conventional tire is 100, and the smaller the wear weight, the better, and a difference of less than 5% is considered equivalent, and there is a difference of more than 10% There are significant differences.
In this test method, since the worn weight is compared, the meaning of the wear resistance test is strong. However, tires with poor partial wear performance wear early, and can be detected in this test. That is, this view can be viewed from both sides of uneven wear resistance and wear resistance.

From Table 1, it can be seen that the inventive tire has improved rolling resistance performance and wear resistance performance compared to the conventional tire. Furthermore, it turns out that the durability example with respect to a side crack is improving the invention example tire compared with the comparative example tire.
Until the ratio CSEh / SWh is 1.25 (Invention Examples 1 to 3, 5 to 8), the durability against side cracks is improved, but even if the ratio CSEh / SWh is changed from 1.25 to 1.36. (Comparison of Invention Examples 3 and 4) Since the durability performance against side cracks is improved only by 1 and the longitudinal spring performance is greatly increased to 2.6, the ratio CSEh / SWh is 1.25 or less. It can be said that the effects of the present invention are sufficiently obtained.
On the other hand, in the comparative tires 1 and 2 in which the ratio CSEh / SWh is 1.0 or less, the durability performance against side cracking tends to surely decrease.
From the above results, it was confirmed that the durability against cracking of the side portion can be improved by setting the ratio CSEh / SWh to exceed 1.0.

1 Bead core 2 Carcass 2a Carcass ply 2b Carcass ply (outermost layer)
2O Carcass ply turn-up part 3a Inclined belt layer 3b Inclined belt layer (outermost layer)
4 circumferential belt layer 5 tread 6 tire 7 rim 10 bead toe

Claims (4)

A carcass made of a carcass ply formed by wrapping a pair of bead cores between the bead portions in a toroidal shape and folded back from the inner side to the outer side in the tire width direction around the bead core, and radially outside the crown portion of the carcass A pneumatic tire in which a belt having at least one inclined belt layer and a tread are arranged in order,
The ratio of the diameter difference BD between the widthwise central portion and the widthwise end of the outermost layer to the width BW of the outermost layer of the inclined belt layer in the tire widthwise cross-section when the tire is mounted on the applicable rim. In the pneumatic tire whose BD / BW is 0.01 or more and 0.04 or less,
The shortest distance CSEh between the tip of the folded portion of at least one layer of the carcass ply and the line segment drawn parallel to the tire rotation axis on the bead toe is the line segment drawn parallel to the tire rotation axis at the maximum tire width position. And a bead toe, which is greater than the shortest distance SWh between a line segment drawn parallel to the tire rotation axis.   With respect to the distance CSH in the tire radial direction between the outermost radial direction of the carcass and the bead toe, the line segment drawn parallel to the tire rotation axis at the maximum width position of the carcass and the bead toe are drawn parallel to the tire rotation axis. 2. The pneumatic tire according to claim 1, wherein a ratio CSWh / CSH of the shortest distance CSWh to the line segment is 0.6 or more and 0.9 or less.   The pneumatic tire according to claim 1 or 2, wherein a ratio SWh / SH of the shortest distance SWh to a cross-sectional height SH of the tire is 0.5 or more and 0.8 or less. The pneumatic tire according to any one of claims 1 to 3, wherein the ratio CSEh / SWh is 1.02 or more and 1.25 or less.

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