Patent Description:
The present invention relates to a retreaded tire.

<CIT> has proposed a retreaded tire formed of a base tire, which is a used tire from which a tread rubber is removed, and a new tread rubber (tread rubber for retread, retreaded tread rubber) attached to the base tire. Related technology is known from <CIT>.

It is possible that damages such as a tread rubber peeling off from a base tire may occur to a retreaded tire during running.

The present invention was made in view of the above, and a primary object thereof is to provide a retreaded tire with improved peeling resistance of the tread rubber to peeling off from the base tire.

A retreaded tire according to claim <NUM> includes a base tire and a tread rubber for retread adhered to the base tire, wherein the tread rubber includes a first tread edge and a first shoulder circumferential groove adjacent to the first tread edge and extending continuously in a tire circumferential direction, and the first shoulder circumferential groove has a groove surface provided with a plurality of dimples.

By adopting the above configuration, the retreaded tire of the present invention can improve the peeling resistance of the tread rubber to peeling off from the base tire.

An embodiment of the present invention will now be described in conjunction with accompanying drawings. <FIG> is a lateral cross-sectional view of a retreaded tire <NUM> (hereinafter may be simply referred to as "tire <NUM>") showing an embodiment of the present invention. <FIG> is the lateral cross-sectional view of the tire <NUM> in a standard state passing all through a tire rotational axis. As shown in <FIG>, the tire <NUM> of the present embodiment includes a base tire (1a), which is obtained by removing a tread rubber from a used tire, and a tread rubber (2a) for retread. This tread rubber (2a) is adhered to the base tire (1a). In <FIG>, bead portions of the base tire (1a) are omitted. The tire <NUM> of the present embodiment is suitable for use as a pneumatic tire for light or medium trucks, for example, but the present invention is not limited to such a mode.

In the case of pneumatic tires for which various standards have been established, the term "standard state" refers to a state in which the tire <NUM> is mounted on a standard rim, inflated to a standard inner pressure, and loaded with no tire load. In the case of tires for which various standards are not established, the standard sate means a state of standard usage according to the purpose of use of the tire and a state in which the tire is not mounted on a vehicle and is loaded with no tire load. In the present specification, unless otherwise noted, dimensions and the like of various parts of the tire are the values measured in the standard sate.

The "standard rim" is a wheel rim specified for the concerned tire by a standard included in a standardization system on which the tire is based, for example, the "normal wheel rim" in JATMA, "Design Rim" in TRA, and "Measuring Rim" in ETRTO.

The "standard inner pressure" is air pressure specified for the concerned tire by a standard included in a standardization system on which the tire is based, for example, the maximum air pressure in JATMA, maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in TRA, and "INFLATION PRESSURE" in ETRTO.

The tire <NUM> includes a tread portion <NUM> including the tread rubber (2a), a pair of sidewall portions <NUM>, and a pair of the bead portions (not shown). The sidewall portions <NUM> are each connected to the tread portion <NUM> on a respective outer side in a tire axial direction and extend in a tire radial direction. The bead portions are each connected to a respective one of the sidewall portions <NUM> on an inner side in the tire radial direction. Further, although the tire <NUM> is provided with known configurations such as a carcass <NUM>, a tread reinforcing layer <NUM>, and the like, descriptions thereof will be omitted here.

The tread rubber (2a) includes a first tread edge T1 and a second tread edge T2. The first tread edge T1 and the second tread edge T2 correspond to axially outermost ground contact positions when the tire <NUM> in the standard state is in contact with a flat surface with zero camber angle by being loaded with <NUM>% of a standard tire load. Thereby, the tread rubber (2a) includes a ground contacting surface (<NUM>), a first buttress surface 8A, and a second buttress surface 8B. The ground contacting surface (<NUM>) is the surface that contacts the road surface when the tire is running and extends axially inward from the first tread edge T1 and the second tread edge T2. The first buttress surface 8A extends axially inward from the first tread edge T1. The second buttress surface 8B extends axially inward from the second tread edge T2.

In the case of pneumatic tires for which various standards have been established, the "standard tire load" refers to a tire load specified for the concerned tire by a standard included in a standardization system on which the tire is based, for example, the "maximum load capacity" in JATMA, maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in TRA, and "LOAD CAPACITY" in ETRTO. Further, in the case of tires for which various standards are not established, the "standard tire load" refers to the maximum load applicable to the use of the tire in accordance with the above-mentioned standards.

<FIG> is a development view showing the ground contacting surface (<NUM>) of the tread rubber (2a). Various grooves are shaded by small dots in <FIG>. As shown in <FIG>, the tread rubber (2a) includes a first shoulder circumferential groove <NUM> adjacent to the first tread edge T1 and extending continuously in a tire circumferential direction. The tread rubber (2a) of the present embodiment includes a second shoulder circumferential groove <NUM> and a crown circumferential groove <NUM> extending continuously in the tire circumferential direction. The second shoulder circumferential groove <NUM> is adjacent to the second tread edge T2. The crown circumferential groove <NUM> is provided between the first shoulder circumferential groove <NUM> and the second shoulder circumferential groove <NUM>, and is located on a tire equator (C) in the present embodiment. Each of the circumferential grooves has a groove width in the range from <NUM> to <NUM>, for example. Further, each of the circumferential grooves has a depth in the range from <NUM> to <NUM>, for example.

The tread rubber (2a) of the present embodiment includes a plurality of land regions <NUM>. The land regions <NUM> includes a first shoulder land region <NUM>, a second shoulder land region <NUM>, a first crown land region <NUM>, and a second crown land region <NUM>. The first shoulder land region <NUM> is demarcated axially outside the first shoulder circumferential groove <NUM> and includes the first tread edge T1. The second shoulder land region <NUM> is demarcated axially outside the second shoulder circumferential groove <NUM> and includes the second tread edge T2. The first crown land region <NUM> is demarcated between the first shoulder circumferential groove <NUM> and the crown circumferential groove <NUM>. The second crown land region <NUM> is demarcated between the second shoulder circumferential groove <NUM> and the crown circumferential groove <NUM>. The tread rubber (2a) of the present embodiment is composed of these four land regions <NUM> but is not limited to such a manner.

<FIG> shows an enlarged perspective view showing a groove surface <NUM> of the first shoulder circumferential groove <NUM>. As shown in <FIG>, the groove surface <NUM> of the first shoulder circumferential groove <NUM> is provided with a plurality of dimples <NUM>. This improves the peeling resistance of the tread rubber (2a) to peeling off from the base tire (1a) (shown in <FIG>, and the same applies hereinafter). The reason for this is as follows. It should be noted that the dimples <NUM> are omitted in <FIG> and <FIG>.

Generally speaking, adhesion between the base tire and the tread rubber is low in retreaded tires. Therefore, the heat generated in the tread rubber during running tends to cause damage such as the tread rubber peeling off from the base tire. In particular, heat generation during running tends to occur at the shoulder portions, where the movement of the tread reinforcing layer is greater, thereby, it is important to reduce the heat generation at the shoulder portions of the tread rubber.

In contrast, in the present invention, heat dissipation around the first shoulder circumferential groove <NUM> is enhanced by a plurality of the dimples <NUM> on the groove surface of the first shoulder circumferential groove <NUM>, therefore, it is possible that the peeling resistance of the tread rubber (2a) to peeling off from the base tire (1a) (hereinafter may be simply referred to as "peeling resistance") is effectively improved.

Further, in an embodiment in which the tread rubber (2a) is adhered to the base tire (1a) by vulcanization and the dimples <NUM> mentioned above are formed by the mold during this vulcanization, since the dimples <NUM> are provided, heat from the mold is easily transferred to the contact area between the tread rubber (2a) and the base tire (1a). Thereby, that the vulcanization process time can be shortened. Further, the dimples <NUM> described above also help to create turbulence in the grooves and reduce noise caused by the first shoulder circumferential groove <NUM> during running. Furthermore, the dimples <NUM> described above can also be expected to have the effect of preventing foreign objects such as stones from getting caught in the first shoulder circumferential groove <NUM>.

Further detailed configurations of the present embodiment will be described below. It should be noted that each of the configurations described below indicates a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exert the effects described above even if it does not have the configurations described below. Further, even if any one of the configurations described below is applied alone to the tire of the present invention having the features described above, performance improvement can be expected in accordance with each configuration. Furthermore, when some of the configurations described below are applied in combination, a combined performance improvement can be expected according to each configuration.

<FIG> is an enlarged development view conceptually illustrating the groove surface <NUM> of the first shoulder circumferential groove <NUM>. In <FIG>, a first groove edge (11a) and a second groove edge (11b) of the first shoulder circumferential groove <NUM> are shown by solid lines. The first groove edge (11a) is the groove edge on the first tread edge T1 side. The second groove edge (11b) is the groove edge on the tire equator (C) side. For ease of understanding the features of the present invention, the grooves and sipes (first shoulder lateral grooves <NUM>, shoulder sipes <NUM>, and crown sipes <NUM> shown in <FIG>) that are connected to these groove edges and extend in the tire axial direction are omitted in <FIG>. Further, fine ridge lines and the like formed on the groove surface <NUM> are also omitted. As shown in <FIG>, the groove surface <NUM> includes a pair of groove wall surfaces <NUM> and a groove bottom surface <NUM> between them. The pair of the groove wall surfaces <NUM> consists of a first groove wall surface <NUM> on the first tread edge T1 side and a second groove wall surface <NUM> on the tire equator (C) side. In <FIG>, a boundary (26a) between the first groove wall surface <NUM> and the groove bottom surface <NUM> and a boundary (26b) between the second groove wall surface <NUM> and the groove bottom surface <NUM> are shown by two-dot chain lines.

As shown in <FIG> and in a region (A) (first region) of <FIG>, the multiple dimples <NUM> are provided on at least one of the pair of the groove wall surfaces <NUM>, specifically, the multiple dimples <NUM> are provided at least on the first groove wall surface <NUM>. In the present embodiment, a plurality of the dimples <NUM> is also provided on the second groove wall surface <NUM>, and in a more preferred embodiment, a plurality of the dimples <NUM> are also provided on the groove bottom surface <NUM>. Thereby, the above-mentioned effects are reliably exerted. However, the present invention is not limited to such a manner. That is, the present invention can include an embodiment in which a plurality of the dimples <NUM> is provided only on the second groove wall surface <NUM>, or an embodiment in which a plurality of the dimples <NUM> is provided only on the groove bottom surface <NUM>.

In another embodiment, at least one of the dimples <NUM> may be formed over the groove bottom surface <NUM> and one of the pair of the groove bottom surfaces <NUM> so as to cross the boundary (26a) or (26b), as in the arrangement shown in a region (B) (second region) in <FIG>. In such an embodiment, the heat dissipation near the boundaries (26a) and (26b) can be further increased, therefore, it is possible that the peeling resistance is further improved. It should be noted that, in the present invention, one first shoulder circumferential groove <NUM> may include the arrangement shown in the region (A) and the arrangement shown in the region (B) in <FIG>. This makes it possible to obtain the above-described effects while maintaining steering stability on a dry road surface (hereinafter may be simply referred to as "steering stability").

As shown in <FIG>, the first shoulder circumferential groove <NUM> is connected with a plurality of the first shoulder lateral grooves <NUM> arranged in the tire circumferential direction and each extending from the first shoulder circumferential groove <NUM> in the tire axial direction on the ground contacting surface (<NUM>) of the tread rubber (2a). Thereby, a <NUM>-pitch area (Pa) is formed between two adjacent first shoulder lateral grooves <NUM> (between the groove center lines) in each pair of the first shoulder lateral grooves <NUM> adjacent to each other. As shown in <FIG>, in each <NUM>-pitch area (Pa), the groove surface <NUM> has one or more rows each having preferably two or more dimples <NUM> arranged in the tire circumferential direction (vertical direction in <FIG>), and more preferably <NUM> or more, even more preferably <NUM> or more, and preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less dimples <NUM> arranged in the tire circumferential direction. Thereby, the above-mentioned effects can be obtained while maintaining the rigidity around the first shoulder circumferential groove <NUM>. Therefore, the steering stability and the peeling resistance are improved in a good balance.

From a similar point of view, it is preferred that one of the groove wall surfaces <NUM> (each of the groove wall surfaces <NUM> in the present embodiment) included in one <NUM>-pitch area (Pa) has one or more rows each having <NUM> to <NUM> dimples <NUM> arranged in the tire radial direction (lateral direction on the groove wall surfaces <NUM> in <FIG>). In other words, it is preferred that one (or each) of the groove wall surfaces <NUM> has one or more rows each having <NUM> to <NUM> dimples <NUM> arranged in the tire radial direction in each <NUM>-pitch area (Pa). As a result, <NUM> to <NUM> dimple rows <NUM> in which a plurality of the dimples <NUM> are arranged in the tire circumferential direction are arranged on one groove wall surface <NUM>. In the present embodiment, one groove wall surface <NUM> has two dimple rows <NUM> arranged therein. However, the present invention is not limited to such a mode.

The groove bottom surface <NUM> has a single row of the dimple row <NUM> in which multiple dimples <NUM> are arranged in the tire circumferential direction. A plurality of the dimple rows <NUM> may be arranged on the groove bottom surface <NUM>.

<FIG> shows a cross-sectional view of one of the dimples <NUM>. As shown in <FIG>, each of the dimples <NUM> has a circular opening, for example. Further, each of the dimples <NUM> extends in a depth direction thereof while maintaining this opening shape. Thereby, each of the dimples <NUM> has an inner space having a cylindrical or a truncated cone shape. However, the present invention is not limited to such an embodiment, and the opening shape of each of the dimples <NUM> may be an ellipse, a triangle, a rectangle, or the like, for example.

As shown in <FIG>, in the present invention, each of the dimples <NUM> has a maximum diameter A1 of <NUM> to <NUM>, preferably <NUM> to <NUM>. Further, each of the dimples <NUM> has a maximum depth (d1) of <NUM> to <NUM>. Therefore, the steering stability and the peeling resistance are improved in a good balance.

Each of the dimples <NUM> includes a concave conical portion having a taper angle θ1. The taper angle θ1 is <NUM> degrees or less, for example, preferably <NUM> to <NUM> degrees. It should be noted that the taper angle θ1 is the angle of an inner wall (25a) with respect to the depth direction of each of the dimples <NUM>. Owing to the above taper angle θ1, it is possible that a large volume of each of the dimples <NUM> is ensured while suppressing cracking of the rubber around the dimples <NUM>.

An angle θ2 between a bottom surface (25d) and the inner wall (25a) is in the range of from <NUM> to <NUM> degrees in each of the dimples <NUM>, for example. The dimples <NUM> configured as such exert excellent heat dissipation at the bottom surfaces (25d), therefore, the peeling resistance is further improved.

As shown in <FIG>, it is preferred that the dimples <NUM> are arranged at an interval (t1) of <NUM> or more and <NUM> or less from each other. Thereby, it is possible that the heat dissipation of the groove surface <NUM> of the first shoulder circumferential groove <NUM> is increased while the durability thereof is maintained. It should be noted the above interval (t1) corresponds to a distance between the edges of two dimples <NUM> adjacent immediately to each other. The interval (t1) shown in <FIG> indicates the distance between two dimples <NUM> in the tire circumferential direction, but the above numerical range also applies to the distance in the tire radial direction between two dimples <NUM> aligned in the tire radial direction.

As shown in <FIG>, the tread rubber (2a) is provided with a plurality of second shoulder lateral grooves <NUM> opening at the ground contacting surface (<NUM>) and the first buttress surface 8A. Each of the second shoulder lateral grooves <NUM> in the present embodiment extends with a constant groove width. On the first buttress surface 8A, a groove width W1 of each of the second shoulder lateral grooves <NUM> is <NUM>% or less of a <NUM>-pitch length P2 between each two of the multiple second shoulder lateral grooves <NUM> adjacent to each other. In a preferred embodiment, the groove width W1 is in the range from <NUM>% to <NUM>% of the <NUM>-pitch length P2. Therefore, the durability near the first tread edge T1 is improved.

<FIG> shows a cross-sectional view taken along A-A line of <FIG>. As shown in <FIG>, a maximum depth (d2) of each of the second shoulder lateral grooves <NUM> is <NUM>% or less of a maximum depth (da) (shown in <FIG> and is the maximum depth not including the dimples <NUM>) of the first shoulder circumferential groove <NUM>. Thereby, the durability near the first tread edge T1 is further improved.

In the cross section of the tread rubber (2a) passing all through the tire rotational axis, the first buttress surface 8A includes an inclined surface <NUM> extending from the first tread edge T1 and a concave arc surface <NUM> arranged radially inside the inclined surface <NUM>. A plane <NUM> is formed between the inclined surface <NUM> and the concave arc surface <NUM>.

The inclined surface <NUM> is a plane that slopes axially outward and radially inward from the first tread edge T1. The inclined surface <NUM> has an angle θ3 in the range from <NUM> to <NUM> degrees with respect to the tire radial direction, for example. Thereby, it is possible that uneven wear around the first tread edge T1 is suppressed.

The concave arc surface <NUM> is concave toward the tire equator (C) (shown in <FIG>) and is curved in an arc shape in a cross section thereof. It is possible that the concave arc surface <NUM> configured as such effectively suppresses heat generation of the first buttress surface 8A. From the point of view of improving the durability and the peeling resistance of the first buttress surface 8A in a good balance, it is preferred that a radius of curvature (r1) of the concave arc surface <NUM> is in the range from <NUM> to <NUM>.

As shown in <FIG>, in the tire <NUM> of the present embodiment, the configuration on the first tread edge T1 side from the tire equator (C) and the configuration on the second tread edge T2 side from the tire equator (C) are substantially the same. That is, the configuration of the first shoulder circumferential groove <NUM> described above can be applied to the second shoulder circumferential groove <NUM>. Further, the configuration of the first buttress surface 8A can be applied to the second buttress surface 8B on the opposite side.

The retreaded tire <NUM> of the present invention can be manufactured by various manufacturing methods. The tire <NUM> of the present invention may be manufactured by attaching the tread rubber (2a) made of unvulcanized rubber to the base tire (1a) and integrating them by vulcanization molding, for example. In this case, it is preferred that the dimples <NUM> (shown in <FIG>) are formed by the mold used during the above-mentioned vulcanization molding. In another manufacturing method, the tire <NUM> of the present invention may be manufactured by, for example, adhering a vulcanized tread rubber (2a) on which the above-mentioned dimples <NUM> are arranged to the base tire (1a), or after the vulcanized tread rubber (2a) without the dimples <NUM> is adhered to the base tire (1a), the dimples <NUM> may be formed on the tread rubber (2a).

While detailed description has been made of the tire according to an embodiment of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiment.

Retreaded tires of size <NUM>/85R16 having the basic structure shown in <FIG> were made by way of test according to the specifications listed in Table <NUM>. As Reference, tires not provided with the dimples on the first shoulder circumferential groove were made by way of test. The tires in the Reference were substantially the same as the tires in Examples except for the above-mentioned items. Each of the test tires was tested for the peeling resistance and other damage. The common specifications and test methods for each test tire are as follows.

Each of the test tires was placed on a drum testing machine and kept running at a speed of <NUM>/h with a vertical load of <NUM> kN, and then the running distance when the retreaded tread peeled off from the base tire was measured. The results are indicated by an index based on the running distance of the Reference being <NUM>, wherein the larger the numerical value, the better the peeling resistance is.

Claim 1:
A retreaded tire comprising:
a base tire (1a); and
a tread rubber (2a) for retread adhered to the base tire (1a),
wherein the tread rubber (2a) includes a first tread edge (T1) and a first shoulder circumferential groove (<NUM>) adjacent to the first tread edge (T1) and extending continuously in a tire circumferential direction, and
the first shoulder circumferential groove (<NUM>) has a groove surface (<NUM>) provided with a plurality of dimples (<NUM>),
the first shoulder circumferential groove (<NUM>) is connected with a plurality of first shoulder lateral grooves (<NUM>) arranged in the tire circumferential direction and each extending in a tire axial direction on a ground contacting surface (<NUM>) of the tread rubber (2a), and
in a <NUM>-pitch area (Pa) between two first shoulder lateral grooves (<NUM>) adjacent to each other, the groove surface (<NUM>) of the first shoulder circumferential groove (<NUM>) is provided with one or more rows each having <NUM> to <NUM> dimples (<NUM>) arranged in the tire circumferential direction,
the tread rubber (2a) includes the ground contacting surface (<NUM>) extending axially inward from the first tread edge (T1) and a first buttress surface (8A) extending inward in a tire radial direction from the first tread edge (T1),
the tread rubber (2a) is provided with a plurality of second shoulder lateral grooves (<NUM>) each opening at the ground contacting surface (<NUM>) and the first buttress surface (8A), and
on the first buttress surface (8A), each of the second shoulder lateral grooves (<NUM>) has a groove width (W1) of <NUM>% or less of a <NUM>-pitch length (P2) between two second shoulder lateral grooves (<NUM>) adjacent to each other,
characterized in that
wherein each of the second shoulder lateral grooves (<NUM>) has a maximum depth (d2) of <NUM>% or less of a maximum depth (da) of the first shoulder circumferential groove (<NUM>).