JP6790606B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

There is a movement to reduce the impact of tires on the fuel efficiency of vehicles and to consider the environment. With the introduction of the labeling system, many users place importance on rolling resistance when selecting tires. From this situation, the development of tires with small rolling resistance is underway.

The mass of the tire affects the rolling resistance. From the viewpoint of small rolling resistance, various studies have been conducted on reducing the weight of tires. An example of this study is disclosed in JP2012-205280.

Studless tires are known as tires for traveling on icy and snowy roads. Soft cross-linked rubber is usually used for the tread of this tire. As a result, the grip is improved and the braking performance on ice and snow roads is ensured.

JP2012-205280A

Weight reduction affects the rigidity of the tire. Therefore, when considering weight reduction due to a small rolling resistance, it is necessary to secure rigidity so that performance such as steering stability is appropriately maintained, for example.

As for studless tires, steering stability and rolling resistance are emphasized as in the case of tires (normal tires) that are considered for running on general road surfaces such as asphalt road surfaces. The studless tires are further required to have further improved braking performance so that the vehicle can run stably on ice and snow roads.

An object of the present invention is to provide a pneumatic tire in which improved braking performance on icy and snowy roads has been achieved.

The pneumatic tire according to the present invention includes a tread, a pair of sidewalls, a pair of clinches, a pair of beads, a carcass and a pair of first sub-apex. Each sidewall extends substantially inward in the radial direction from the end of the tread. Each clinch extends substantially inward in the radial direction from the edge of the sidewall. Each bead is located axially inside the clinch. The carcass spans between one bead and the other along the inside of the tread and sidewalls. Each first sub-apex extends radially outward along the carcass on the radial outside of the bead. In the contour of the carcass, the radial outer end of the contour is the first reference point, the straight line extending radially through the first reference point is the first reference line, and the axial outer end of the contour is the first. When two reference points are set and a straight line extending in the axial direction through the second reference point is used as the second reference line, this contour has a center on the first reference line and passes through the first reference point. Includes a center arc extending substantially outward in the axial direction from the reference point, and a lower arc having a center on the second reference line and passing through the second reference point and extending substantially inward in the radial direction from the second reference point. There is. The ratio of the radius of the lower arc to the radius of the center arc is 0.10 or more. The complex elastic modulus of the first sub-apex is 60 MPa or more.

Preferably, in this pneumatic tire, the distance from the bead baseline to the radial inner end of the lower arc is 0.6 or less of the distance from the bead baseline to the second reference point.

Preferably, in this pneumatic tire, the distance from the first reference line to the axially outer end of the center arc is 0.2 or more and 0.4 of the distance from the first reference line to the second reference point. It is as follows.

Preferably, in this pneumatic tire, the ratio of the radius of the lower arc to the radius of the center arc is 0.30 or less.

Preferably, the pneumatic tire further comprises a pair of second sub-apex. Each second sub-apex extends radially outward along the carcass inside the first sub-apex in the axial direction. The complex elastic modulus of the second sub-apex is 0.80 or more and 1.20 or less of the complex elastic modulus of the first sub-apex.

In the pneumatic tire according to the present invention, the first sub-apex has a high elastic modulus. This first sub-apex contributes to the in-plane torsional rigidity of the tire.

In a conventional tire, the ratio of the radius of the lower arc included in the contour of the carcass to the radius of the center arc is generally less than 0.10. On the other hand, in this tire, the ratio of the radius of the lower arc to the radius of the center arc is 0.10 or more. In this tire, the radius of the lower arc included in the contour of the carcass is larger than that of the conventional tire. The contour of the carcass including the lower arc contributes to the prevention of distortion concentration. In this tire, the force applied to the tire through the rim propagates throughout the tire without being concentrated in a particular area. In this tire, the energy loss due to deformation is effectively suppressed.

In this tire, the synergistic action of the first sub-apex and the contour of the carcass is aimed at dramatically improving the in-plane torsional rigidity. This tire has excellent steering stability. With this tire, the force input from the rim is efficiently propagated to the tread. This tire exhibits good braking performance on icy and snowy roads. Since energy loss is suppressed, this tire also suppresses an increase in rolling resistance.

With this tire, improvement in braking performance on icy and snowy roads is achieved while suppressing an increase in rolling resistance and a decrease in steering stability. According to the present invention, it is possible to obtain a pneumatic tire in which improved braking performance on icy and snowy roads is achieved.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG. FIG. 3 is a schematic view showing the outline of the carcass on the tire of FIG. FIG. 4 is an enlarged cross-sectional view showing a part of a pneumatic tire according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

FIG. 1 shows the pneumatic tire 2. In detail, FIG. 1 shows a part of a cross section of the tire 2 along a plane including the central axis of rotation of the tire 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, the alternate long and short dash line CL represents the equatorial plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equatorial plane except for the tread pattern.

The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of wings 8, a pair of clinches 10, a pair of beads 12, a carcass 14, a belt 16, a band 18, a pair of edge bands 20, an inner liner 22, and a pair. It is equipped with a chafer 24 and a pair of first sub-apex 26s. This tire 2 is a tubeless type. The tire 2 is mounted on a passenger car.

The tread 4 has a shape that is convex outward in the radial direction. The tread 4 forms a tread surface 28 that is in contact with the road surface. A groove 30 is carved in the tread 4. A tread pattern is formed by the groove 30. The tread 4 has a base layer 32 and a cap layer 34. The cap layer 34 is laminated on the base layer 32. The base layer 32 is made of crosslinked rubber having excellent adhesiveness. The cap layer 34 is made of crosslinked rubber having excellent wear resistance, heat resistance and grip.

Usually, for the cap layer 34, a crosslinked rubber having a complex elastic modulus E * (hereinafter, may be simply expressed as an elastic modulus ET) set in the range of 5 MPa or more and 10 MPa or less is used.

In the present invention, the complex elastic modulus E * of each member constituting the tire 2 is measured in accordance with the provisions of "JIS K 6394". In this measurement, a plate-shaped test piece (length = 45 mm, width = 4 mm, thickness = 2 mm) is used. This test piece may be cut out from the tire 2, or a sheet may be prepared from a rubber composition for a member whose complex elastic modulus E * is to be measured and cut out from this sheet. The measurement conditions are as follows.
Viscoelastic spectrometer: "VESF-3" from Iwamoto Seisakusho
Initial distortion: 10%
Dynamic distortion: ± 1%
Frequency: 10Hz
Deformation mode: Tension measurement temperature: 70 ° C

Each sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is made of crosslinked rubber having excellent cut resistance and weather resistance. The sidewall 6 prevents damage to the carcass 14.

Each wing 8 is joined to each of the tread 4 and sidewall 6. The wing 8 is made of a crosslinked rubber having excellent adhesiveness.

Each clinch 10 extends substantially inward in the radial direction from the edge of the sidewall 6. The clinch 10 is located outside the bead 12 and the carcass 14 in the axial direction. The clinch 10 is made of crosslinked rubber having excellent wear resistance. The clinch 10 comes into contact with the flange of the rim.

Each bead 12 is located axially inward of the clinch 10. The bead 12 includes a core 36 and an apex 38 extending radially outward from the core 36. The core 36 is ring-shaped and includes a wound non-stretchable wire. A typical material for wire is steel. Apex 38 is tapered outward in the radial direction.

In this tire 2, the complex elastic modulus E * of Apex 38 (hereinafter, may be simply expressed as elastic modulus EA) is appropriately set in the range of 60 MPa or more and 70 MPa or less. The Apex 38 is made of a high hardness crosslinked rubber.

The carcass 14 includes a carcass ply 40. The carcass 14 of the tire 2 is composed of one carcass ply 40. The carcass 14 may be composed of two or more carcass plies 40.

In this tire 2, the carcass ply 40 is straddled between the beads 12 on both sides and runs along the inside of the tread 4 and the sidewall 6. The carcass ply 40 is folded back from the inside to the outside in the axial direction around each core 36. Due to this folding, the carcass ply 40 is formed with a main portion 42 and a pair of folding portions 44. The carcass ply 40 includes a main portion 42 and a pair of folded portions 44. The main portion 42 bridges between one core 36 and the other core 36. Each folded portion 44 extends radially outward from the core 36.

Although not shown, the carcass ply 40 consists of a large number of parallel cords and topping rubber. The absolute value of the angle each code makes with respect to the equatorial plane is 75 ° to 90 °. In other words, the carcass 14 has a radial structure. The cord consists of organic fibers. Preferred organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

The belt 16 is laminated with the carcass 14. The belt 16 reinforces the carcass 14. The belt 16 is composed of an inner layer 46 and an outer layer 48. Although not shown, each of the inner layer 46 and the outer layer 48 consists of a number of parallel cords and topping rubbers. Each cord is tilted with respect to the equatorial plane. The general absolute value of the tilt angle is 10 ° or more and 35 ° or less. The direction of inclination of the cord of the inner layer 46 with respect to the equatorial plane is opposite to the direction of inclination of the cord of the outer layer 48 with respect to the equatorial plane. The preferred material for the cord is steel. Organic fibers may be used for the cord. The axial width of the belt 16 is preferably 0.7 times or more the maximum width of the tire 2. The belt 16 may include three or more layers.

The band 18 is located on the outer side in the radial direction of the belt 16. In the axial direction, the width of the band 18 is equivalent to the width of the belt 16. Although not shown, the band 18 consists of a cord and a topping rubber. The cord is wound in a spiral. The band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 16 is restrained by this cord, the lifting of the belt 16 is suppressed. The cord consists of organic fibers. Preferred organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

Each edge band 20 is located on the radial outside of the belt 16 and near the end of the belt 16. Although not shown, the edge band 20 comprises a cord and a topping rubber. The cord is wound in a spiral. The edge band 20 has a so-called jointless structure. The cord extends substantially in the circumferential direction. Since the end of the belt 16 is restrained by this cord, the lifting of the belt 16 is suppressed. The cord consists of organic fibers. Preferred organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

The inner liner 22 is located inside the carcass 14. The inner liner 22 is joined to the inner surface of the carcass 14. The inner liner 22 is made of crosslinked rubber having excellent air shielding properties. A typical base rubber of the inner liner 22 is butyl rubber or halogenated butyl rubber. The inner liner 22 holds the internal pressure of the tire 2.

Each chafer 24 is located in the vicinity of the bead 12. When the tire 2 is incorporated into the rim, the chafer 24 comes into contact with the rim. This contact protects the vicinity of the bead 12. In this embodiment, the chafer 24 comprises a cloth and rubber impregnated in the cloth. The chafer 24 may be integrated with the clinch 10. In this case, the material of the chafer 24 is the same as that of the clinch 10.

Each first sub-apex 26 is located radially outside the bead 12. The radial inner portion of the first sub-apex 26 is located between the carcass 14 and the clinch 10 in the axial direction. The radial outer portion of the first sub-apex 26 is located between the carcass 14 and the sidewall 6 in the axial direction.

FIG. 2 shows a part of the cross section of the tire 2 shown in FIG. In FIG. 2, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2.

In FIG. 2, the tire 2 is incorporated in the rim 50. This rim 50 is a regular rim. The state of the tire 2 shown in FIG. 2 is a state in which the tire 2 is incorporated in the rim 50 and the tire 2 is filled with air so as to have a normal internal pressure, that is, an inflated state.

In the present invention, unless otherwise specified, the dimensions and angles of each member of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. When the tire 2 is for a passenger car, the dimensions and angles are measured with an internal pressure of 180 kPa unless otherwise specified.

As used herein, the term "regular rim" means a rim defined in the standard on which Tire 2 relies. The "standard rim" in the JATTA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

As used herein, the normal internal pressure means the internal pressure defined in the standard on which the tire 2 relies. The "maximum air pressure" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

In the present specification, the normal load means the load defined in the standard on which the tire 2 relies. The "maximum load capacity" in the JATTA standard, the "maximum value" in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

In this tire 2, the first sub-apex 26 extends radially outward along the carcass 14 on the radial outside of the bead 12. A folded-back portion 44 is located between the first sub-apex 26 and the apex 38. The end 52 of the folded-back portion 44 is covered with the first sub-apex 26.

In this tire 2, the inner end 54 of the first sub-apex 26 is located inside the outer end 56 of the apex 38 in the radial direction. In this tire 2, the first sub-apex 26 overlaps with the apex 38 in the axial direction.

In this tire 2, the first sub-apex 26 has the maximum thickness near the outer end 56 of the apex 38. The first sub-apex 26 has an inwardly tapered shape on the inner side in the radial direction from the portion having the maximum thickness. The first sub-apex 26 has an outwardly tapered shape on the outer side in the radial direction from the portion having the maximum thickness.

FIG. 3 shows a part of the outline (also referred to as a case line) of the carcass 14. In FIG. 3, the vertical direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2.

The contour of the carcass 14 shown in FIG. 3 is specified on the inflated tire 2. Specifically, a cross-sectional image of the tire 2 taken by a computer tomography method using X-rays (hereinafter, X-ray CT method) is taken into a CAD (Computer-aided design), and the carcass 14 is displayed on the CAD. The outline of is specified. In particular, this contour is identified by a line drawn along the outer surface of the main portion 42 of the carcass ply 40. Although not shown, the outline of the carcass 14 may be specified by a line drawn along the cord included in the main portion 42. In specifying the contour of the carcass 14, no load is applied to the tire 2.

In FIG. 3, reference numeral P1 is the radial outer end of the contour of the carcass 14. In the present invention, this outer end P1 is referred to as a first reference point. The alternate long and short dash line L1 is a straight line extending in the radial direction. This straight line L1 passes through the first reference point P1. In the present invention, the straight line L1 extending in the radial direction through the first reference point P1 is referred to as the first reference line. In the tire 2, the first reference line L1 coincides with the equatorial plane CL. Reference numeral P2 is an axially outer end of the contour of the carcass 14. In the present invention, this outer end P2 is referred to as a second reference point. The solid line L2 is a straight line extending in the axial direction. This straight line L2 passes through the second reference point P2. In the present invention, the straight line L2 extending in the axial direction through the second reference point P2 is referred to as a second reference line.

In this tire 2, the contour of the carcass 14 includes a large number of arcs arranged in parallel in the axial direction. In particular, in this tire 2, the contour of the carcass 14 is composed of a large number of arcs arranged in parallel in the axial direction. One arc is in contact with another arc located next to this one arc.

In FIG. 3, the arrow Rc represents the radius of one arc that constitutes the contour of the carcass 14. Although not shown, the center of this arc is located on the first reference line L1. This arc passes through the first reference point P1. This arc extends substantially outward in the axial direction from the first reference point P1. Reference numeral Pc is the end of this arc, specifically, the axially outer end of this arc. In the present invention, an arc having a center on the first reference line L1 and extending substantially outward in the axial direction from the first reference point P1 is referred to as a center arc. In this tire 2, the contour of the carcass 14 includes a center arc. In the case of the passenger car tire 2, the radius Rc of this center arc is appropriately set in the range of 300 mm or more and 700 mm or less.

In FIG. 3, the arrow Ru represents the radius of an arc different from the above-mentioned center arc that constitutes the contour of the carcass 14. The symbol Cu is the center of this arc. As shown in FIG. 3, the center Cu of the arc having the radius Ru is located at the second reference line L2. This arc passes through the second reference point P2. This arc extends substantially inward in the radial direction from the second reference point P2. The symbol Pu is the end of this arc, specifically, the radial inner end of this arc. In the present invention, an arc having a central Cu on the second reference line L2 and extending substantially inward in the radial direction from the second reference point P2 is referred to as a lower arc. In the tire 2, the contour of the carcass 14 includes a lower arc in addition to the center arc described above. That is, the contour of the carcass 14 includes a center arc and a lower arc.

In this tire 2, the complex elastic modulus E * (hereinafter, may be simply expressed as the elastic modulus E1) of the first sub-apex 26 is 60 MPa or more. The first apex 38 has a high elastic modulus. The first sub-apex 26 is made of a high hardness crosslinked rubber. The first apex 38 contributes to the in-plane torsional rigidity of the tire 2.

From the viewpoint of in-plane torsional rigidity, the higher the elastic modulus E1 of the first sub-apex 26 is, the more preferable it is. However, if the elastic modulus E1 is too high, the riding comfort may be deteriorated. The elastic modulus E1 of the tire 2 is preferably 70 MPa or less from the viewpoint of maintaining a good ride comfort.

In this tire 2, the ratio of the radius Ru of the lower arc to the radius Rc of the center arc is 0.10 or more. With conventional tires, this ratio is generally less than 0.10. In this tire 2, the radius Ru of the lower arc included in the contour of the carcass 14 is larger than that of the conventional tire. The contour of the carcass 14 including the lower arc contributes to the prevention of distortion concentration. In the tire 2, the force input to the tire 2 through the rim 50 propagates to the entire tire 2 without being concentrated on a specific part. In this tire 2, the loss of energy due to deformation is effectively suppressed. From this point of view, this ratio is preferably 0.14 or more.

In this tire 2, the in-plane torsional rigidity is dramatically improved by the synergistic action of the contours of the first sub-apex 26 and the carcass 14. The tire 2 has excellent steering stability. In the tire 2, the force input from the rim 50 is efficiently propagated to the tread 4. The tire 2 exhibits good braking performance on icy and snowy roads. Since energy loss is suppressed, the increase in rolling resistance is also suppressed in this tire 2. In particular, when the cap layer 34 of the tread 4 is soft as in a studless tire, the contours of the first sub-apex 26 and the carcass 14 act synergistically to dramatically improve braking performance on icy and snowy roads. improves.

With this tire 2, improvement in braking performance on icy and snowy roads is achieved while suppressing an increase in rolling resistance and a decrease in steering stability. According to the present invention, it is possible to obtain a pneumatic tire 2 in which the braking performance on an ice-snow road is improved.

In the tire 2, the ratio of the radius Ru of the lower arc to the radius Rc of the center arc is preferably 0.30 or less. This prevents the contour of the carcass 14 from becoming distorted at the bead 12. In this tire 2, strain is unlikely to concentrate on the bead 12 portion even when a large load is applied. This tire 2 has excellent durability. Moreover, since the force input from the rim 50 is efficiently propagated to the tread 4, good braking performance is maintained in the tire 2. Since energy loss is also suppressed, rolling resistance is unlikely to increase with this tire 2. From this point of view, this ratio is more preferably 0.26 or less.

In FIG. 3, the solid BBL is the bead baseline. The bead baseline is a line that defines the rim diameter of the rim 50 (see JATTA). This bead baseline extends axially. The double-headed arrow HB is the radial distance from the bead baseline to the second reference point P2. The double-headed arrow Hu is the radial distance from the bead baseline to the end Pu of the lower arc. The double-headed arrow H is the radial distance from the bead baseline to the first reference point P1.

In this tire 2, the distance Hu is preferably 0.6 or less of the distance HB. In other words, the ratio of the distance Hu to the distance HB is preferably 0.6 or less. By setting this ratio to 0.6 or less, the contour of the carcass 14 is configured such that the lower arc having a large radius Ru has a large length. The contour of the carcass 14 contributes to the prevention of distortion concentration. In the tire 2, the force input to the tire 2 through the rim 50 propagates to the entire tire 2 without being concentrated on a specific part. In this tire 2, the loss of energy due to deformation is effectively suppressed. The contour of the carcass 14 contributes to the in-plane torsional rigidity. Since the force input from the rim 50 is efficiently propagated to the tread 4, the tire 2 exhibits good braking performance on icy and snowy roads. From this point of view, this ratio is more preferably 0.5 or less, and even more preferably 0.4 or less. From the viewpoint of improving the performance of the tire 2, a smaller ratio is preferable, but from the viewpoint of easiness of manufacturing the tire 2, this ratio is preferably 0.2 or more.

In the tire 2, the distance HB with respect to the distance H from the viewpoint that the lower arc having a large length and a large radius Ru in the contour of the carcass 14 effectively contributes to the improvement of the in-plane torsional rigidity. The ratio of is preferably 0.4 or more, and preferably 0.7 or less.

In FIG. 3, the double-headed arrow WB is the axial distance from the first reference line L1 to the second reference point P2. The double-headed arrow Wc is the axial distance from the first reference line L1 to the end Pc of the center arc.

In this tire 2, the distance Wc is preferably 0.2 or more, preferably 0.4 or less of the distance WB. In other words, the ratio of the distance Wc to the distance WB is preferably 0.2 or more, and preferably 0.4 or less. By setting this ratio to 0.2 or more, the contour of the carcass 14 effectively contributes to the configuration of the flat tread surface 28. Since the tire 2 is in sufficient contact with the road surface, good braking performance and steering stability can be obtained with the tire 2. By setting this ratio to 0.4 or less, the influence of the contour of the carcass 14 on the ground pressure distribution is effectively suppressed. In this tire 2, it is difficult to form a portion having a locally high contact pressure on the contact patch. The tire 2 has excellent durability because uneven wear and the like are effectively prevented.

In the tire 2, the distance HB with respect to the distance WB from the viewpoint that the lower arc having a large length and a large radius Ru in the contour of the carcass 14 effectively contributes to the improvement of the in-plane torsional rigidity. The ratio of is preferably 0.8 or more, and preferably 1.4 or less.

In FIG. 2, the double-headed arrow H1 is the radial distance from the bead baseline to the outer end 58 of the first sub-apex 26. This distance H1 is the radial height of the first sub-apex 26. The double-headed arrow HF is the radial distance from the bead baseline to the end 52 of the folded portion 44. This distance HF is the height of the folded-back portion 44 in the radial direction. The double-headed arrow HA is the radial distance from the bead baseline to the outer edge 56 of the apex 38. This distance HA is the radial height of the Apex 38.

In this tire 2, the ratio of the height H1 of the first sub-apex 26 to the radial distance HB from the bead baseline to the second reference point P2 is preferably 0.8 or more, preferably 1.1 or less. By setting this ratio to 0.8 or more, the first sub-apex 26 effectively contributes to the in-plane torsional rigidity. With this tire 2, good braking performance and steering stability can be obtained. By setting this ratio to 1.1 or less, the influence of the first sub-apex 26 on the mass of the tire 2 can be suppressed. The tire 2 maintains a small rolling resistance.

In this tire 2, the ratio of the height HF of the folded-back portion 44 to the distance HB is preferably 0.4 or more, and preferably 0.6 or less. When this ratio is set to 0.4 or more, the folded-back portion 44 contributes to the rigidity. By setting this ratio to 0.6 or less, the influence of the folded-back portion 44 on the mass of the tire 2 can be suppressed.

In this tire 2, the ratio of the height HA of the Apex 38 to the distance HB is preferably 0.2 or more, and preferably 0.3 or less. By setting this ratio to 0.2 or more, the rigidity of the bead 12 is appropriately maintained. By setting this ratio to 0.3 or less, the influence of Apex 38 on the mass of the tire 2 can be suppressed.

In FIG. 2, the solid line LF is the normal of the outer surface of the first sub-apex 26. This normal LF passes through the end 52 of the folded-back portion 44. The double-headed arrow tf is the thickness of the first sub-apex 26 measured along this normal LF. In the present invention, this thickness tf is the thickness of the first sub-apex 26 at the end 52 of the folded-back portion 44. The solid line LA is the normal of the outer surface of the first sub-apex 26. This normal LA passes through the outer edge 56 of the Apex 38. The double-headed arrow ta is the thickness of the first sub-apex 26 measured along this normal LA. In the present invention, this thickness ta is the thickness of the first sub-apex 26 at the outer end 56 of the apex 38.

In this tire 2, the thickness tf is preferably 1 mm or more and 3 mm or less. By setting the thickness tf to 1 mm or more, the first sub-apex 26 effectively contributes to the in-plane torsional rigidity. With this tire 2, good braking performance and steering stability can be obtained. By setting this thickness tf to 3 mm or less, the influence of the first sub-apex 26 on the mass of the tire 2 can be suppressed. The tire 2 maintains a small rolling resistance.

In this tire 2, the thickness ta is preferably 3 mm or more and 5 mm or less. By setting the thickness ta to 3 mm or more, the first sub-apex 26 effectively contributes to the in-plane torsional rigidity. With this tire 2, good braking performance and steering stability can be obtained. Moreover, since the first sub-apex 26 arranges the folded-back portion 44 so as to be close to the main portion 42, the occurrence of looseness in the folded-back portion 44 is prevented. This tire 2 is also excellent in durability. By setting this thickness ta to 5 mm or less, the influence of the first sub-apex 26 on the mass of the tire 2 can be suppressed. The tire 2 maintains a small rolling resistance.

In this tire 2, the ratio of the thickness tf to the thickness ta is preferably 0.4 or more and 0.6 or less. When this ratio is set to 0.4 or more, the first apex 38 effectively contributes to the in-plane torsional rigidity as a whole. With this tire 2, good braking performance and steering stability can be obtained. By setting this ratio to 0.6 or less, the influence of the first sub-apex 26 on the mass of the tire 2 is effectively suppressed. The tire 2 maintains a small rolling resistance.

As described above, in this tire 2, the apex 38 is made of crosslinked rubber. The first sub-apex 26 is also made of crosslinked rubber. In the tire 2, from the viewpoint of productivity, the first sub-apex 26 is preferably made of a cross-linked rubber equivalent to the cross-linked rubber of the apex 38. In other words, it is preferred that the apex 38 and the first sub-apex 26 are formed by cross-linking the same rubber composition.

In the manufacture of the tire 2, a plurality of rubber members are assembled to obtain a low cover (unvulcanized tire 2). This low cover is put into the mold. The outer surface of the low cover is in contact with the cavity surface of the mold. The inner surface of the low cover abuts on the bladder or rigid core. The low cover is pressurized and heated in the mold. The low cover rubber composition flows by pressurization and heating. The rubber undergoes a cross-linking reaction by heating, and the tire 2 is obtained. By using a mold having an uneven pattern on the cavity surface, an uneven pattern is formed on the tire 2. From the viewpoint of easy control of the contour of the carcass 14, in the manufacture of the tire 2, a low cover is manufactured on a rigid core, and the rigid core is brought into contact with the inner surface of the low cover to form the inner surface of the tire 2. Is preferable.

FIG. 4 shows a part of the pneumatic tire 72 according to another embodiment of the present invention. FIG. 4 is a drawing corresponding to FIG. 2 described above. In FIG. 4, the vertical direction is the radial direction of the tire 72, the left-right direction is the axial direction of the tire 72, and the direction perpendicular to the paper surface is the circumferential direction of the tire 72.

The tire 72 is further provided with a second sub-apex 74. The tire 72 has the same configuration as the tire 2 shown in FIG. 1 except for the second sub-apex 74. Therefore, in FIG. 4, the same members as the members of the tire 2 of FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 4, reference numeral P2 is an axially outer end of the contour of the carcass 14. The solid BBL is the bead baseline.

The tire 72 includes a pair of second sub-apex 74s. Each second sub-apex 74 extends radially outward along the carcass 14 inside the first sub-apex 26 in the axial direction.

As shown in FIG. 4, in the radial direction, the position of the inner end 76 of the second sub-apex 74 substantially coincides with the position of the outer end 56 of the apex 38. The inner end 76 of the second sub-apex 74 may be located radially inside the outer end 56 of the apex 38. In this case, in order to suppress the influence on the mass of the tire 72, the second sub with respect to the outer end 56 of the apex 38 so that the overlapping length of the second sub apex 74 and the apex 38 is 5 mm or less. The position of the inner end 76 of the apex 74 is adjusted. The inner end 76 of the second sub-apex 74 may be located radially outside the outer end 56 of the apex 38, but in this case the second sub-apex to avoid sudden fluctuations in rigidity. The position of the inner end 76 of the second sub-apex 74 with respect to the outer end 56 of the apex 38 is adjusted so that the distance between the 74 and the apex 38 is 5 mm or less.

In this tire 72, the outer end 78 of the second sub-apex 74 is located near the axially outer end P2 of the contour of the carcass 14. As shown in FIG. 4, the outer end 78 of the second sub-apex 74 is covered with the first sub-apex 26. The outer end 78 of the second sub-apex 74 is located radially inside the outer end 58 of the first sub-apex 26. The outer end 78 of the second sub-apex 74 may be located radially outside the outer end 58 of the first sub-apex 26. By the way, when the position of the outer end 78 of the second sub-apex 74 coincides with the position of the outer end 58 of the first sub-apex 26 in the radial direction, the strain is concentrated on the outer end 58 and the outer end 78. There is a fear. Therefore, from the viewpoint of suppressing the concentration of strain and maintaining good durability, the outer end 78 of the second sub-apex 74 should not coincide with the outer end 58 of the first sub-apex 26 in the radial direction. The position of the outer end 58 of the first sub-apex 26 with respect to the outer end 78 of the second sub-apex 74 is adjusted. In this case, the first sub-apec with respect to the outer end 78 of the second sub-apex 74 so that the distance from the outer end 78 of the second sub-apex 74 to the outer end 58 of the first sub-apex 26 is 3 mm or more. The position of the outer end 58 of the screw 26 is adjusted.

As described for tire 2 shown in FIG. 1, the first sub-apex 26 has the maximum thickness near the outer end 56 of the apex 38. The first sub-apex 26 has an inwardly tapered shape on the inner side in the radial direction from the portion having the maximum thickness. The first sub-apex 26 has an outwardly tapered shape on the outer side in the radial direction from the portion having the maximum thickness. On the other hand, the second sub-apex 74 has a substantially uniform thickness as a whole. The second sub-apex 74 has a sheet shape. As shown in FIG. 4, the volume of the second sub-apex 74 is smaller than the volume of the first sub-apex 26.

In this tire 72, the first sub-apex 26 has a high elastic modulus. As will be described later, the second sub-apex 74 also has the same elastic modulus as the first sub-apex 26. The second sub-apex 74 is made of a high hardness crosslinked rubber. In the tire 72, the first sub-apex 26 and the second sub-apex 74 synergistically contribute to the in-plane torsional rigidity of the tire 72.

In the tire 72, as in the tire 2 shown in FIG. 1, the ratio of the radius Ru of the lower arc to the radius Rc of the center arc is 0.10 or more. In this tire 72, the radius of the lower arc included in the contour of the carcass 14 is larger than that of the conventional tire 2. The contour of the carcass 14 including the lower arc contributes to the prevention of distortion concentration. In the tire 72, the force input to the tire 72 through the rim 50 propagates to the entire tire 72 without concentrating on a specific part. In the tire 72, the loss of energy due to deformation is effectively suppressed.

In this tire 72, the in-plane torsional rigidity is dramatically improved by the synergistic action of the contours of the first sub-apex 26, the second sub-apex 74, and the carcass 14. The tire 72 has excellent steering stability. In the tire 72, the force input from the rim 50 is efficiently propagated to the tread 4. The tire 72 exhibits good braking performance on icy and snowy roads. Since the energy loss is suppressed, the increase in rolling resistance is also suppressed in this tire 72. With the tire 72, improvement in braking performance on icy and snowy roads is achieved while suppressing an increase in rolling resistance and a decrease in steering stability.

As described above, the second sub-apex 74 of the tire 72 has the same elastic modulus as the first sub-apex 26. In particular, in this tire 72, the complex elastic modulus E * of the second sub-apex 74 (hereinafter, may be simply expressed as the elastic modulus E2) is the complex elastic modulus E * of the first sub-apex 26, that is, The elastic modulus E1 is preferably 0.80 or more, and preferably 1.20 or less. In other words, the ratio of the elastic modulus E2 to the elastic modulus E1 is preferably 0.80 or more, and preferably 1.20 or less. When this ratio is set to 0.80 or more, the second sub-apex 74 together with the first sub-apex 26 effectively contributes to the in-plane torsional rigidity. Since the force input to the tire 72 through the rim 50 propagates to the entire tire 72 without being concentrated on a specific part, energy loss is effectively suppressed. With this tire 72, rolling resistance is unlikely to increase. From this point of view, this ratio is more preferably 0.90 or more. By setting this ratio to 1.20 or less, the influence of the second sub-apex 74 on the rigidity balance of the entire tire 72 can be appropriately suppressed. Good braking performance and steering stability are properly maintained in the tire 72. From this point of view, this ratio is more preferably 1.10 or less.

In FIG. 4, the double-headed arrow H2 is the radial distance from the bead baseline to the outer end 78 of the second sub-apex 74. This distance H2 is the radial height of the second sub-apex 74. The double-headed arrow HB is the radial distance from the bead baseline to the outer end P2.

In this tire 72, the ratio of the height H2 of the second sub-apex 74 to the radial distance HB from the bead baseline to the second reference point P2 is preferably 0.8 or more, preferably 1.1 or less. By setting this ratio to 0.8 or more, the second sub-apex 74 effectively contributes to the in-plane torsional rigidity. With this tire 72, good braking performance and steering stability can be obtained. By setting this ratio to 1.1 or less, the influence of the second sub-apex 74 on the mass of the tire 72 is suppressed. The tire 72 maintains a small rolling resistance.

In FIG. 4, the double-headed arrow H1 is the radial height of the first sub-apex 26, the double-headed arrow HF is the radial height of the folded-back portion 44, and the double-headed arrow HA is the radial height of the apex 38. is there. Further, the double-headed arrow ta is the thickness of the first sub-apex 26 measured along the normal line LA, and the double-headed arrow tf is the thickness of the first sub-apex 26 measured along the normal line LF. ..

Also in this tire 72, as in the tire 72 shown in FIG. 1, the ratio of the height H1 of the first sub-apex 26 to the distance HB is preferably 0.8 or more, and preferably 1.1 or less. The ratio of the height HF of the folded-back portion 44 to the distance HB is preferably 0.4 or more, and preferably 0.6 or less. The ratio of the height HA of Apex 38 to the distance HB is preferably 0.2 or more, and preferably 0.3 or less. The thickness tf is preferably 1 mm or more and 3 mm or less. The thickness ta is preferably 3 mm or more and 5 mm or less. The ratio of the thickness tf to the thickness ta is preferably 0.4 or more and 0.6 or less.

In this tire 72, the apex 38 is made of crosslinked rubber. The first sub-apex 26 is also made of crosslinked rubber. As described above, the second sub-apex 74 is also made of crosslinked rubber. From the viewpoint of productivity, the first sub-apex 26 is preferably made of a cross-linked rubber equivalent to the cross-linked rubber of the apex 38. From the same viewpoint, the second sub-apex 74 is preferably made of a cross-linked rubber equivalent to the cross-linked rubber of the apex 38. Particularly preferably, the first sub-apex 26 and the second sub-apex 74 are made of a cross-linked rubber equivalent to the cross-linked rubber of the apex 38, that is, the apex 38, the first sub-apex 26 and the second sub-apex. 74 is formed by cross-linking the same rubber composition.

Hereinafter, the effects of the present invention will be clarified by Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.

[Example 1]
The tire shown in Fig. 1-3 was manufactured. The size of this tire is 215 / 60R16. In Example 1, the radius Rc of the center arc was 540 mm. The ratio (Ru / Rc) of the radius Ru of the lower arc to the radius Rc was 0.19. The ratio (Hu / HB) of the radial distance Hu from the bead baseline to the inner end Pu of the lower arc to the radial distance HB from the bead baseline to the second reference point P2 was 0.33. The ratio (Wc / WB) of the distance Wc from the first reference line L1 to the outer end Pc of the center arc to the axial distance WB from the first reference line L1 to the second reference point P2 was 0.24. .. The elastic modulus E1 of the first sub-apex was 65 MPa.

In this Example 1, the ratio of the height HA of the apex to the radial distance HB from the bead baseline to the outer end P2 was 0.24. The elastic modulus EA of Apex was 65 MPa.

[Comparative Example 1]
Comparative Example 1 is a conventional tire. The first sub-apex is not provided in this comparative example 1. The specifications of this Comparative Example 1 are as shown in Table 1 below.

[Example 2-6]
In the same manner as in Example 1 except that the radius Ru of the lower arc was changed so that the ratio (Ru / Rc) and the ratio (Hu / HB) were as shown in Table 1 below. I got a tire.

[Example 7-10]
Tires of Example 7-10 were obtained in the same manner as in Example 1 except that the ratio (Wc / WB) was as shown in Table 2 below.

[Examples 11-13 and Comparative Example 2]
Tires of Examples 11-13 and Comparative Example 2 were obtained in the same manner as in Example 1 except that the elastic modulus E1 was set as shown in Table 3 below.

[Example 14]
A tire of Example 13 was obtained in the same manner as in Example 1 except that the second sub-apex shown in FIG. 4 was further provided. The elastic modulus E2 of this second sub-apex was 65 MPa. The ratio of elastic modulus E2 to elastic modulus E1 (E2 / E1) was 1.00.

[Example 15-18]
Tires of Examples 15-18 were obtained in the same manner as in Example 14 except that the elastic modulus E1 and elastic modulus E2 and the ratio (E2 / E1) were as shown in Table 4 below.

[Rolling resistance coefficient]
The rolling resistance coefficient (RRC) was measured under the following measurement conditions using a rolling resistance tester.
Rim used: 6.5JJ (made of aluminum alloy)
Internal pressure: 210 kPa
Load: 5.42 kN
Speed: 80km / h
The results are shown in the index in Table 1-4 below. The smaller the value, the more preferable.

[Brake property (ICE)]
The tire was assembled into a regular rim and the tire was filled with air so that the internal pressure was 220 kPa. This tire was installed in a passenger car with a displacement of 1200 cc. The driver was allowed to drive this passenger car on a mirror burn-like ice road test course in an environment of -5 ° C, and evaluated the braking performance on ice. In this evaluation, the stopping distance required to step on the lock brake at a speed of 20 km / h and stop it was measured. The results are shown in the index in Table 1-4 below. The larger the value, the shorter the stopping distance, which is preferable.

[Brake property (SNOW)]
The tire was assembled into a regular rim and the tire was filled with air so that the internal pressure was 220 kPa. This tire was installed in a passenger car with a displacement of 1200 cc. The driver was asked to drive this passenger car on a snowy road test course and evaluated the braking performance on snow. In this evaluation, the stopping distance required to step on the lock brake at a speed of 20 km / h and stop it was measured. The results are shown in the index in Table 1-4 below. The larger the value, the shorter the stopping distance, which is preferable.

[In-plane torsional rigidity]
The in-plane torsional rigidity was measured under the following measurement conditions using a sidewall rigidity tester.
Rim used: 6.5JJ
Internal pressure: 230 kPa
The results are shown in the index in Table 1-4 below. The larger the value, the greater the in-plane torsional rigidity.

[durability]
The tire was incorporated into a regular rim, and the tire was filled with air to set the internal pressure to 250 kPa. This tire was mounted on a drum type running tester, and a vertical load of 9.14 kN was applied to the tire. The tire was run at a speed of 100 km / h on a drum with a radius of 1.7 m. The mileage until the tire broke was measured. The results are shown in the index in Table 1-4 below. The larger the value, the more preferable.

As shown in Table 1-4, the tires of the examples have a higher evaluation than the tires of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

The configuration described above can also be applied to various tires.

2, 72 ... Tires 4 ... Treads 6 ... Sidewalls 10 ... Clinch 12 ... Beads 14 ... Carcass 16 ... Belts 26 ... First Sub Apex 36 ...・ Core 38 ・ ・ ・ Apex 40 ・ ・ ・ Carcass ply 42 ・ ・ ・ Main part 44 ・ ・ ・ Folded part 50 ・ ・ ・ Rim 52 ・ ・ ・ Folded part 44 end 54 ・ ・ ・ First sub apex 26 Inner end 56 ・ ・ ・ Outer end of apex 38 58 ・ ・ ・ Outer end of first sub-apex 26 74 ・ ・ ・ Second sub-apex 76 ・ ・ ・ Inner end of second sub-apex 74 78 ・・ ・ Outer end of the second sub-apex 74

Claims (4)

It has a tread, a pair of sidewalls, a pair of clinches, a pair of beads, a carcass and a pair of first sub-apex.
Each sidewall extends substantially inward in the radial direction from the end of the tread.
Each clinch extends substantially inward in the radial direction from the edge of the sidewall.
Each bead is located axially inside the clinch above,
The bead has a core and an apex extending radially outward from this core.
The apex is made of crosslinked rubber having a complex elastic modulus of 60 MPa or more and 70 MPa or less.
The carcass spans between one bead and the other along the inside of the tread and sidewalls.
Each first sub-apex extends radially outward along the carcass on the radial outside of the bead.
The radial inner portion of the first sub-apex is located between the carcass and the clinch in the axial direction, and the radial outer portion of the first sub-apex is the carcass and the sidewall in the axial direction. Located between and
In the contour of the carcass, the radial outer end of the contour is the first reference point, the straight line extending radially through the first reference point is the first reference line, and the axial outer end of the contour is the first. When the two reference points are set and the straight line extending in the axial direction through the second reference point is set as the second reference point,
This contour has a center arc centered on the first reference line, passes through the first reference point, and extends substantially outward in the axial direction from the first reference point, and has a center on the second reference line and is the first. It includes a lower arc that passes through the two reference points and extends substantially inward in the radial direction from this second reference point.
The ratio of the radius of the lower arc to the radius of the center arc is 0.10 or more and 0.30 or less .
A pneumatic tire having a complex elastic modulus of 60 MPa or more in the first sub-apex. It has a tread, a pair of sidewalls, a pair of clinches, a pair of beads, a carcass and a pair of first sub-apex.
Each sidewall extends substantially inward in the radial direction from the end of the tread.
Each clinch extends substantially inward in the radial direction from the edge of the sidewall.
Each bead is located axially inside the clinch above,
The bead has a core and an apex extending radially outward from this core.
The apex is made of crosslinked rubber having a complex elastic modulus of 60 MPa or more and 70 MPa or less.
The carcass spans between one bead and the other along the inside of the tread and sidewalls.
Each first sub-apex extends radially outward along the carcass on the radial outside of the bead.
The radial inner portion of the first sub-apex is located between the carcass and the clinch in the axial direction, and the radial outer portion of the first sub-apex is the carcass and the sidewall in the axial direction. Located between and
In the contour of the carcass, the radial outer end of the contour is the first reference point, the straight line extending radially through the first reference point is the first reference line, and the axial outer end of the contour is the first. When the two reference points are set and the straight line extending in the axial direction through the second reference point is set as the second reference point,
This contour has a center arc centered on the first reference line, passes through the first reference point, and extends substantially outward in the axial direction from the first reference point, and has a center on the second reference line and is the first. It includes a lower arc that passes through the two reference points and extends substantially inward in the radial direction from this second reference point.
The ratio of the radius of the lower arc to the radius of the center arc is 0.10 or more.
The complex elastic modulus of the first sub-apex is 60 MPa or more.
The distance from the first reference line to the axially outer end of the center arc, is 0.2 to 0.4 of the distance from the first reference line of the to the second reference point, air-filled tires. The pneumatic tire according to claim 1 or 2 , wherein the distance from the bead baseline to the radial inner end of the lower arc is 0.6 or less of the distance from the bead baseline to the second reference point. It also has a pair of second sub-apex
Each second sub-apex extends radially outward along the carcass inside the first sub-apex in the axial direction.
The pneumatic tire according to any one of claims 1 to 3 , wherein the complex elastic modulus of the second sub-apex is 0.80 or more and 1.20 or less of the complex elastic modulus of the first sub-apex.

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