JP2008308155A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire in which an eccentric wear characteristic of a tire shoulder part is improved by making its ground contact configuration and contact pressure distribution appropriate with competitive cost. <P>SOLUTION: The pneumatic radial tire includes a plurality of circumferential main grooves 1a, 1b, lug grooves 2 extending almost in a tire width direction and a tread pattern forming a plurality of land part lines 4a, 4b on a tire tread surface T. In the land part lines 4b of the tire shoulder parts including ground contact ends E, the lug grooves 2, which extend to the ground contact ends E from the circumferential main grooves 1b closest to the ground contact ends E, terminate near the ground contact ends E. Land parts L are formed which continue in a circumferential direction near the ground contact ends E. Intermittent slit secondary grooves 3 are formed almost parallel to the main grooves 1b on the main groove 1b side of the land part lines 4b of the tire shoulder parts. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, and more particularly, to a pneumatic radial tire that improves the uneven wear performance of a tire shoulder portion by optimizing the contact shape and contact pressure distribution while maintaining cost competitiveness.

  Today, in a pneumatic tire, for example, as described in Patent Document 1, by arranging a belt reinforcing layer between a belt layer and a tread, the tread portion of the tire has a radius due to centrifugal force during high-speed running. It is known that large diameter growth can be suppressed to the outside in the direction, and thus this reduces heat generation and distortion at the belt end to improve high-speed durability and improve steering stability. It is generally done.

However, without providing such a belt reinforcing layer, a conventional steel belt structure (hereinafter referred to as “hereinafter referred to as“ the steel belt structure ”) including only two belt plies in which steel cords inclined in opposite directions to the tire circumferential direction are embedded. Tires abbreviated as “two steel belt structures” are still widely used today because they do not have a belt reinforcement layer and thus have a small number of members and high cost competitiveness. In particular, for tires of a size that can be mounted on a light vehicle or a compact car, each automobile manufacturer adopts such a two-steel belt structure tire and emphasizes high cost competitiveness.
Japanese Patent Laid-Open No. 2005-112065

  However, the two-steel belt structure tire has a narrower belt width than the ground contact width for manufacturing and durability reasons, and therefore the ply diameter growth cannot be constrained by the belt layer near the belt end of the shoulder portion. It was inevitable that the tread surface grew greatly in the radial direction due to centrifugal force during high-speed running. Thus, when the diameter growth of the shoulder portion is large, there is a problem in that a circumferential length difference occurs between the center portion and shoulder uneven wear due to driving occurs in the shoulder portion having a long circumferential length.

  In addition, in the two steel belt structure, there is no belt reinforcement layer such as a cap or a layer, so that belt buckling occurs, and there is a risk of wiping trying to wrap the shoulder block inward within the ground plane. . The occurrence of uneven shoulder wear is also caused by the occurrence of shearing force in the tire width direction due to such wiping.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire that improves the uneven wear performance of the tire shoulder portion by optimizing the contact shape and contact pressure distribution while maintaining cost competitiveness.

  As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by employing a predetermined tread pattern and belt structure, and have completed the present invention.

In other words, the pneumatic radial tire of the present invention includes a plurality of circumferential main grooves and lug grooves extending substantially in the tire width direction on a tire road surface portion, and a pneumatic radial tire having a tread pattern that forms a plurality of land portion rows. In
In the shoulder portion land portion row including the ground contact end, a lug groove extending from the circumferential main groove closest to the ground contact end to the ground contact end terminates in the vicinity of the ground contact end and continues in the circumferential direction near the ground contact end. And a discontinuous slit subgroove substantially parallel to the main groove on the main groove side of the shoulder portion land portion row.

  In the pneumatic radial tire of the present invention, it is preferable that the groove width of the lug groove of the shoulder portion land portion row gradually decreases from the side communicating with the main groove toward the end side. In addition, a carcass layer whose both ends in the width direction are folded around a bead core and extend in a toroidal shape, and a steel cord disposed radially outside the carcass layer and inclined in directions opposite to each other in the tire circumferential direction And a belt layer composed of two belt plies embedded in the belt, and preferably does not include a belt protective layer for protecting the belt layer. Furthermore, it is preferable that a crown radius of curvature R1 of the shoulder portion is 500 mm or more and a radius of curvature R2 of the ground contact end portion of the shoulder portion is 20 mm or less.

  In the pneumatic radial tire of the present invention, it is possible to improve the uneven wear performance of the tire shoulder portion by making the contact shape and contact pressure distribution appropriate while maintaining cost competitiveness.

Hereinafter, embodiments of the present invention will be specifically described.
FIG. 1 is a developed view of a tread portion of a pneumatic radial tire (hereinafter abbreviated as “tire”) 10 according to a preferred embodiment of the present invention. In the tire 10 of the present invention, the tire road surface portion T includes a plurality of, in the illustrated preferred example, three circumferential main grooves 1a and 1b and lug grooves 2 extending substantially in the tire width direction. (Center part land part row | line | column 4a, shoulder part land part row | line | column 4b) are formed.

  Here, in the present invention, the lug groove 2 extending from the circumferential main groove 1b closest to the ground end to the ground end E is terminated in the vicinity of the ground end E in the shoulder portion land portion row 4b including the ground end E. However, it is important to form the land portion L that is continuous in the circumferential direction in the vicinity of the ground contact end portion E. Preferably, the groove width of the lug groove 2 of the shoulder portion land portion row 4b is gradually decreased from the side communicating with the main groove 1b toward the end 9 side.

  By preventing the lug groove 2 from being completely removed at the ground contact edge E, the shoulder land land row 4b including the ground contact edge E is formed as a continuous land L. As a result, the so-called heel-and-toe uneven wear at the ground contact edge E of the shoulder land portion row 4b can be suppressed.

  Further, by gradually reducing the width of the lug groove 2 of the shoulder portion land portion row 4b from the side communicating with the main groove 1b toward the terminal end 9 side, adjacent blocks in the shoulder portion land portion row 4b can be mutually connected. This is preferable because they are more constrained.

  Further, in the present invention, as shown in the figure, it is important to provide the intermittent slit sub-groove 3 substantially parallel to the main groove 1b on the main groove 1b side of the shoulder portion land portion row 4b. When the tread rubber of the shoulder portion is compressed and expanded in the circumferential direction at the time of grounding, the grounding length is increased. By expanding the rubber inside the slit sub-groove 3 provided in the shoulder block, the grounding length is increased. Can be prevented.

  Next, FIG. 2 shows a cross-sectional structure of the tire 10. As shown in FIG. 2, the tire 10 includes a pair of bead portions 13 each having a bead core 12 embedded therein, sidewall portions 14 extending from the bead portions 13 toward the outside in a substantially radial direction, and the sidewall portions 14. And a substantially cylindrical tread portion 15 for connecting the outer ends in the radial direction.

  Further, the tire 10 has a carcass layer 16 that extends between the bead cores 12 in a toroidal shape and reinforces the sidewall portions 14 and the tread portions 15, and both end portions in the width direction of the carcass layer 16 are around the bead cores 12. It is folded back from the axially inner side toward the axially outer side. The carcass layer 16 is composed of at least one carcass ply 17 and 18 in the illustrated preferred example, and the carcass plies 17 and 18 have a cord angle of 60 to 90 degrees with respect to the tire circumferential direction. A large number of mutually parallel carcass cords made of organic fiber cords such as nylon and aromatic polyamide or steel cords, which are crossed, that is, extending in the radial direction (meridian direction), are embedded.

  A belt layer 20 is disposed on the radially outer side of the carcass layer 16, and this belt layer 20 is formed by laminating at least two belt plies, preferably two inner belt plies 21 and outer belt plies 22 as shown. It is composed of two steel belt structures.

  Here, a plurality of mutually parallel steel cords are respectively embedded in the belt plies 21 and 22, and these steel cords are composed of stranded wires or monofilaments. The steel cords in the two belt plies 21 and 22 are inclined in the opposite direction to the tire circumferential direction and intersect each other. The driving angle of the steel cords in the belt plies 21 and 22 is preferably 10 ° to 40 ° with respect to the tire circumferential direction.

  By adopting a known two-steel belt structure that does not have a belt protective layer as in the above preferred example, a tire having high cost competitiveness can be obtained.

  Moreover, in the suitable example of this invention, it is preferable that the crown curvature radius R1 of the shoulder part 23 is 500 mm or more, and the curvature radius R2 of the grounding edge part 24 of the shoulder part 23 is 20 mm or less. In this way, by increasing the crown curvature radius R1 of the shoulder portion 23, the ground contact surface of the shoulder portion is brought into contact with the road surface at once, while the curvature radius R2 of the ground contact end portion 24 of the shoulder portion 23 is decreased. The contact pressure is concentrated on the end portion, and as a result, a large frictional force is generated, so that wiping can be suppressed as a stopper against shearing in the tire width direction.

  In the present invention, various grooves and sipes can be provided in the tread as long as the functions of the groove and belt structure described above are not impaired. In the preferred example shown, the lug groove 6 and the curved slit subgroove 7 communicating with the lug groove 6 are formed in the center land portion row 4a. In addition, the shoulder land land row 4b is formed with an intermittent slit sub-groove 3 and a slit sub-groove 5 that communicates in a substantially vertical direction at a substantially middle portion thereof. Furthermore, a short lug groove 8 is formed in the ground contact end portion E of the shoulder portion land portion row 4b.

Hereinafter, the present invention will be specifically described based on examples.
Example 1
A tire having the tread pattern and the two steel belt structure shown in FIG.
Tire size: 155 / 65R13 73S
Tread width TW: 120mm
Negative rate: 32%
Width of circumferential main groove 1a: 8 mm, width of 1b: 9.1 mm
Depth of circumferential main grooves 1a and 1b: 6.0 mm
Width of the portion of the lug groove 2 communicating with the circumferential main groove 1b: 2.5 to 4.5 mm (varies depending on the pitch)
Lug groove 2 depth: 5 mm
Width L of land L: 5mm
Intermittent slit secondary groove 3 width: 1.5 mm
Intermittent slit sub-groove 3 depth: 5 mm
Curvature radius R1: 1000mm
Curvature radius R2: 5mm

(Conventional example 1)
A known tire having the tread pattern and the two steel belt structure shown in FIG.
Tire size: 155 / 65R13 73S
Tread width: 110mm
Negative rate: 28%
Curvature radius R1: 90m
Curvature radius R2: 17mm

(Evaluation methods)
In this evaluation method, the rim size is 4.00B × 13, and the internal pressure is based on the pneumatic-load capability correspondence table corresponding to the radial ply tire size defined by JATMEAREAR BOOK (1992, Japan Automobile Tire Association Standard). Set.
The test tire was mounted on an actual vehicle, the vehicle traveled on a distance of 7500 km, and the following evaluation items were tested.
1) Ratio of wear amount between the shoulder portion and the center portion of the front wheel (wear ratio)
= Shoulder wear / center wear (the closer to 1, the more uniform wear)
2) Step amount on the shoulder block and stepped side on the kick side = Heel and toe step amount (The smaller the step, the better)
The obtained results are shown in Table 1 below.

  From the evaluation results in Table 1, it was confirmed that the tire of Example 1 had higher shoulder-to-shoulder wear resistance and heel-and-toe uneven wear performance than the tire of Conventional Example 1.

(Example 2)
In addition to the tread pattern shown in FIG. 4 and the two steel belt structure, a tire having one belt reinforcing layer and satisfying the following conditions was manufactured as a prototype.
Tire size: 195 / 65R15 91H
Tread width TW: 140mm
Negative rate: 34%
Width of circumferential main groove 1a: 9 mm, width of 1b: 10.5 mm
Depth of circumferential main grooves 1a and 1b: 7.5 mm
Width of the portion of the lug groove 2 communicating with the circumferential main groove 1b: 2.5 to 4.5 mm (varies depending on the pitch)
Lug groove 2 depth: 5 mm
Width L of land L: 5mm
Intermittent slit secondary groove 3 width: 2 mm
Intermittent slit secondary groove 3 depth: 6 mm
Curvature radius R1: 145mm
Curvature radius R2: 36mm

(Conventional example 2)
In addition to the tread pattern shown in FIG. 5 and the two steel belt structure, a known tire having one belt reinforcing layer and satisfying the following conditions was adopted as Conventional Example 2.
Tire size: 195 / 65R15 91H
Tread width: 140mm
Negative rate: 34%
Width of circumferential main groove 1a: 9 mm, width of 1b: 10.5 mm
Depth of circumferential main grooves 1a and 1b: 7.5 mm
Width of the portion of the lug groove 2 communicating with the circumferential main groove 1b: 2.5 to 4.5 mm (varies depending on the pitch)
Lug groove 2 depth: 5 mm
Curvature radius R1: 145mm
Curvature radius R2: 36mm

(Wear energy measurement method)
FIG. 6 is a schematic diagram showing a method for measuring wear energy. In Example 2 and Conventional Example 2, the wear energy at points A to G on the tires 30 and 31 shown in FIGS. 4 and 5 was measured according to the following method. A and B are points at the end of the shoulder portion (SHO2) of the tire, C to E are points at the inside of the shoulder portion of the tire (SHO1), and F and G are points of the center portion (CL) of the tire. It is a point.
1) The point to be measured among the points A to G on the tires 30 and 31 shown in FIGS. 4 and 5 is Y, and when this Y rolls on the measurement table 32, the point X on the measurement table 32 Set to pass through.
2) The tires 30 and 31 are rolled at a speed of 0.2 km / h, and the point Y on the tires 30 and 31 is kicked again by the 3-component force sensor embedded in the X point with the force when stepping on the X point. The deviation (movement amount) of the point Y at the moment of dashi is observed with a non-contact optical motion sensor (manufactured by Applied Research Laboratory), the wear energy (unit: J / m) is measured, and the wear ratio (1 And the difference in wear energy tickling (unit: J / m) was determined.
The obtained results are shown in FIGS.

  FIG. 7 is a graph showing the wear energy distribution at points A to G, and FIG. 8 is a graph showing the average value of the wear energy at the center portion and the shoulder portion. In FIG. 7, ◯ indicates Example 2, and ▲ indicates Conventional Example 2. Further, in FIG. 8, the plain indicates Example 2 and the shaded portion indicates Conventional Example 2. In FIG. 7, the difference in wear energy was small in the center portion (points F and G), whereas in the shoulder portion, the difference in wear energy was small in Example 2, whereas in Conventional Example 2, There was a large difference in wear energy, particularly at points A and B. In FIG. 8, the difference in wear energy between Example 2 and Conventional Example 2 was small at the center (points F and G), but Example 2 and Conventional Example 2 were obtained at the shoulder (A to E). The wear energy was significantly different.

  FIG. 9 is a graph showing the wear ratio of the shoulder portion with respect to the center portion. It is the ratio of the average value of the wear energy at the shoulder portion to the average value of the wear energy at the center portion, and the closer the wear ratio is to 1, the more the wear is prevented. As shown in FIG. 9, in Example 2, the wear ratio is 1.25, whereas in Conventional Example 2, the wear ratio is 1.79, and the tire of Example 2 is more than the tire of Conventional Example 2, It was shown that the wear was prevented.

FIG. 10 is a graph showing the heel and toe evaluation of the shoulder portion end. The wear energy tickling difference (J / m) was determined by EW ₂ −EW ₁ with the wear energy at point B being (EW ₂ ) and the wear energy at point A being (EW ₁ ). In Example 2, it was 0.02 × 10 ³ (J / m), whereas in Conventional Example 2, it was 0.15 × 10 ³ (J / m).

  From the evaluation results of FIGS. 7 to 10, it was confirmed that the tire of Example 2 had higher shoulder-to-shoulder wear resistance and heel-and-toe uneven wear performance than the tire of Conventional Example 2.

FIG. 3 is a development view in which a tread portion of a tire according to a preferred embodiment of the present invention is developed. FIG. 2 is a cross-sectional view in the width direction of the tire shown in FIG. 1. FIG. 6 is a development view in which a tread portion of a tire of Conventional Example 1 is developed. FIG. 3 is a development view in which a tread portion of a tire according to a preferred embodiment of the present invention is developed. FIG. 6 is a development view in which a tread portion of a tire of Conventional Example 2 is developed. It is a schematic diagram which shows the measuring method of wear energy. It is a graph which shows the wear energy distribution in points A-G. It is a graph which shows the average value of the wear energy in a center part and a shoulder part. It is a graph which shows the wear ratio of the shoulder part with respect to a center part. It is a graph which shows the heel and toe evaluation of a shoulder part edge part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Circumferential main groove 2 Lug groove 3 Intermittent slit subgroove 4a Center part land part row 4b Shoulder part land part row 5 Slit subgroove 6,8 Lag groove 7 Curved slit subgroove 9 Termination 10, 30, 31 Tire 12 Bead core 13 Bead portion 14 Side wall portion 15 Tread portion 16 Carcass layer 17, 18 Carcass ply 20 Belt layer 21 Inner belt ply 22 Outer belt ply 23 Shoulder portion 24 Grounding end portion 32 Measuring base CL Tire center portion SHO1 Tire shoulder Inside SHO2 tire shoulder end

Claims (4)

In a pneumatic radial tire having a tread pattern that includes a plurality of circumferential main grooves and lug grooves extending substantially in the tire width direction on a tire road surface portion, and forms a plurality of land portion rows,
In the shoulder portion land portion row including the ground contact end, a lug groove extending from the circumferential main groove closest to the ground contact end to the ground contact end terminates in the vicinity of the ground contact end and continues in the circumferential direction near the ground contact end. And a discontinuous slit subgroove substantially parallel to the main groove on the main groove side of the shoulder portion land portion row.   The pneumatic radial tire according to claim 1, wherein the width of the lug groove of the shoulder portion land portion row gradually decreases from the side communicating with the main groove toward the end side.   A carcass layer whose ends in the width direction are folded around a bead core and extend in a toroidal shape, and a steel cord that is disposed radially outside the carcass layer and is inclined in opposite directions to the tire circumferential direction is embedded inside A pneumatic radial tire according to any one of claims 1 to 3, further comprising a belt layer made of two belt plies and having no belt protective layer for protecting the belt layer.   The pneumatic radial tire according to claim 3, wherein a crown radius of curvature R1 of the shoulder portion is 500 mm or more and a radius of curvature R2 of the ground contact end portion of the shoulder portion is 20 mm or less.

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