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

A motorcycle tire with a plurality of oblique grooves in a tread portion is proposed in <CIT>. This motorcycle tire is expected to maintain wet performance and improve transient characteristics during cornering by specifying angles of the oblique grooves.

<CIT> discloses a motorcycle tire comprising the features according to the preamble of claim <NUM>.

<CIT> discloses a motorcycle tire comprising features according to a related technology.

<CIT> also discloses a motorcycle tire comprising features according to a related technology.

In recent years, there has been a demand for improvement in fuel efficiency of motorcycles. In addition, electric motorcycles, which are becoming popular in recent years, are expected to increase their driving range on a single charge. In order to meet these needs, a reduction in rolling resistance of motorcycle tires is required.

The present invention was made in view of the above, and a primary object thereof is to provide a motorcycle tire with reduced rolling resistance.

This object is satisfied by a motorcycle tire comprising the features according to claim <NUM>.

The motorcycle tire includes a tread portion, wherein the tread portion includes a first tread edge, a second tread edge, and a ground contact surface defined between the first tread edge and the second tread edge, the ground contact surface is curved in an arc shape so as to be convex outward in a tire radial direction, the ground contact surface includes a central region and a first outer region, the central region is configured to contact a ground during straight running with zero camber angle, and includes a first outer edge in a tire axial direction located on the first tread edge side and a second outer edge in the tire axial direction located on the second tread edge side, the first outer region is defined on the first tread edge side of the first outer edge of the central region, the ground contact surface is provided with a plurality of oblique grooves each including a portion inclined with respect to a tire circumferential direction, each of the oblique grooves extends across the central region and the first outer region, each of the oblique grooves includes a vertical groove portion extending at an angle α of <NUM> degrees or less with respect to the tire circumferential direction, and a minimum distance in the tire axial direction along the ground contact surface between the vertical groove portion and the first outer edge of the central region is <NUM>% or less of a maximum width in the tire axial direction of the central region along the ground contact surface.

It is possible that the motorcycle tire of the present invention reduces the rolling resistance by adopting the above configuration.

An embodiment of the present invention will now be described in conjunction with accompanying drawings. <FIG> shows a lateral cross-sectional view of a motorcycle tire <NUM> (hereinafter may simply be referred to as "tire") according to an embodiment of the present invention in a standard state. <FIG> is a development view showing a tread pattern of a tread portion <NUM> of the tire <NUM>. <FIG> is an A-A cross sectional view of <FIG>. The tire <NUM> is suitable for scooters, for example.

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 have not been established, the aforementioned standard state means the state of standard use of the tire for its intended purpose, unmounted on the vehicle and loaded with no tire load. In the present specification, unless otherwise noted, the dimensions and the like of various parts of the tire are the values measured in the standard state. Further, in the present specification, unless otherwise noted, known methods can be applied as appropriate to measure the dimensions.

The term "standard rim" refers to 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 term "standard inner pressure" refers to 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.

As shown in <FIG>, the tire <NUM> includes a first tread edge T1, a second tread edge T2, and a ground contact surface (<NUM>) therebetween. The first tread edge T1 and the second tread edge T2 correspond to the edges of the ground contact surface (<NUM>) and contact the road surface when cornering at the maximum camber angle. Further, the ground contact surface (<NUM>) is curved in an arc shape so as to be convex outward in a tire radial direction. The tire <NUM> configured as such can obtain sufficient ground contact area even during cornering with a large camber angle.

The tire <NUM> has internal components provided in a general motorcycle, such as a carcass, a belt layer, and the like. Known configurations may be employed as appropriate for these.

As shown in <FIG>, the tread portion <NUM> has a directional pattern in which a rotational direction (R) is specified. The rotational direction (R) is indicated by letters or symbols on sidewall portions <NUM> (shown in <FIG>), for example.

As shown in <FIG> and <FIG>, d. The central region <NUM> means a region that contacts a plane when the tread portion <NUM> of the tire <NUM> in the standard state is in contact with the plane with zero camber angle by being loaded with <NUM>% of a standard tire load. In <FIG>, outer edges (5e) of the central region <NUM> are indicated by a chain double-dashed line. The outer edges (5e) are a first outer edge (5el) positioned on the first tread edge T1 side and a second outer edge (5e2) positioned on the second tread edge T2 side.

As shown in <FIG>, a maximum width W1 of the central region <NUM> is appropriately adjusted according to various configurations such as curvature of the ground contact surface (<NUM>) of the tread portion <NUM>, the carcass, the belt layer, and the like. The maximum width W1 of the central region <NUM> is from <NUM>% to <NUM>% of a tread ground contacting width TW, for example. It should be noted that the maximum width W1 is the maximum width in a tire axial direction of the central region <NUM> along the ground contact surface (<NUM>) in the standard state. The tread ground contacting width TW is the distance along the ground contact surface (<NUM>) from the first tread edge T1 to the second tread edge T2 in the standard state.

As shown in <FIG>, the tread portion <NUM> includes a first tread portion 2A defined between the first tread edge T1 and a tire equator (C) and a second tread portion 2B defined between the second tread edge T2 and the tire equator C. The first tread portion 2A and the second tread portion 2B have a pattern that is substantially line symmetrical with respect to the tire equator (C), except that they are displaced in a tire circumferential direction of the tire. Therefore, the configuration described in the present specification for the first tread portion 2A can be applied to the second tread portion 2B. However, the present invention is not limited to such an aspect, and the pattern of the tread portion <NUM> may be asymmetric with respect to the tire equator (C).

The ground contact surfaces (<NUM>) include a first outer region <NUM> and a second outer region <NUM>. The first outer region <NUM> is a region on the first tread edge T1 side of the first outer edge (5e1) of the central region <NUM>. The second outer region <NUM> is a region on the second tread edge T2 side of the second outer edge (5e2) of the central region <NUM>. Further, the ground contact surface (<NUM>) is provided with a plurality of oblique grooves <NUM> including portions inclined with respect to the tire circumferential direction. The oblique grooves <NUM> are provided in each of the first tread portion 2A and the second tread portion 2B. The features of the present invention will be described below based on the oblique grooves <NUM> provided in the first tread portion 2A.

<FIG> shows an enlarged view of the first tread portion 2A of <FIG>. As shown in <FIG>, each of the oblique grooves <NUM> extends across the central region <NUM> and the first outer region <NUM>. Further, each of the oblique grooves <NUM> includes a vertical groove portion <NUM> extending at an angle α of <NUM> degrees or less with respect to the tire circumferential direction.

<FIG> shows an enlarged view of one of the oblique grooves <NUM>. As shown in <FIG>, a minimum distance L1 in the tire axial direction along the ground contact surface (<NUM>) between the vertical groove portion <NUM> and the first outer edge (5e1) in the first tread portion 2A of the central region <NUM> is <NUM>% or less of the maximum width W1 (shown in <FIG>) in the tire axial direction. It should be noted that the minimum distance L1 means the minimum distance from the above-mentioned first outer edge (5e) to the groove edge of the vertical groove portion <NUM>. The tire <NUM> of the present invention can reduce the rolling resistance by adopting the above configuration. The mechanism is as follows.

Motorcycle tires with the ground contact surface (<NUM>) curved in an arc shape have large distortion near the outer edges (5e) of the central region <NUM> of the tread portion <NUM> that touches the ground during straight running. This distortion also tends to increase the rolling resistance. In the present invention, the vertical groove portions <NUM> of the oblique grooves <NUM> are located near the outer edges (5e) of the central region <NUM>, therefore, the strain described above can be alleviated, thereby, the rolling resistance can be reduced. In addition, in the present invention, since the rolling resistance can be reduced independent of the rubber composition of the tread portion <NUM>, maintenance of handling performance and anti-wear performance can also be expected.

A more detailed configuration of the embodiment of the present invention will be described below. It should be noted that each configuration described below represents a specific aspect of the embodiment. Therefore, it goes without saying that the present invention can achieve the effects described above even if it does not have the configuration 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, an improvement in performance according to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a combined improvement in performance can be expected according to the combination.

As shown in <FIG>, the oblique grooves <NUM> are inclined to a toe side in the rotational direction (R) as it goes from the tire equator (C) side to the first tread edge T1 side, for example. As a result, in each of the oblique grooves <NUM>, an inner end (10a) on the tire equator (C) side is positioned on a heel side, which comes into contact with the ground first, in the rotational direction (R), and an outer end (10b) on the first tread edge T1 side is positioned on a toe side, which comes into contact with the ground last, in the rotational direction (R). The oblique grooves <NUM> configured as such can exert excellent drainage performance by utilizing tire rotation.

The oblique grooves <NUM> are fit between tire equator (C) and the first tread edge T1. That is, the inner ends (10a) of the oblique grooves <NUM> are located on the first tread edge T1 side from the tire equator (C). The outer ends (10b) of the oblique grooves <NUM> are located on the tire equator (C) side from the first tread edge T1. However, the oblique grooves <NUM> are not limited to such an aspect, and may cross the tire equator (C) or open at the first tread edge T1. It should be noted that the inner end (10a) and the outer end (10b) are the ends of a groove centerline of each of the oblique grooves <NUM>.

A distance L2 in the tire axial direction from the tire equator (C) to the inner end (10a) of each of the oblique grooves <NUM> is <NUM>% or less of the tread ground contacting width TW. A distance L3 in the tire axial direction from the first tread edge T1 to the outer end (10b) of each of the oblique grooves <NUM> is <NUM>% or less of the tread ground contacting width TW. The distance L2 and distance L3 mentioned above mean the distances along the ground contact surface (<NUM>). Hereinafter, in the present specification, unless otherwise specified, the distances and lengths of various parts are meant to be along the ground contact surface (<NUM>).

In a preferred embodiment, in at least one pair of the oblique grooves <NUM> adjacent to each other in the tire circumferential direction, the inner ends (10a) are arranged at different positions in the tire axial direction from each other. Similarly, in at least one pair described above, the outer ends (10b) of the oblique grooves <NUM> are arranged at different positions in the tire axial direction. The arrangement of the oblique grooves <NUM> configured as such helps to suppress uneven wear near the tire equator (C) and near the first tread edge T1.

As shown in <FIG>, each of the oblique grooves <NUM> includes at least one bent portion <NUM>. Each of the oblique grooves <NUM> includes a plurality of the bent portions <NUM>. The bent portions <NUM> are portions where groove edges (10e) of the oblique grooves <NUM> are bent. Of the two groove edges (10e) forming each of the bent portions <NUM>, for the groove edge (10e) with the larger radius of curvature, the radius of curvature is smaller than the groove width of each of the oblique grooves <NUM>.

Each of the vertical groove portion <NUM> is formed between two bent portions <NUM>. The vertical groove portions <NUM> extend linearly. However, they are not limited to such a mode, and the vertical groove portions <NUM> may extend in a curved manner. It is preferred that a maximum groove width W2 (shown in <FIG>) of each of the vertical groove portions <NUM> is <NUM>% or more of the maximum groove width of each of the oblique grooves <NUM>. The oblique grooves <NUM> extend with a substantially constant groove width, and the groove width of each of the vertical groove portions <NUM> is the same as the groove width of the other portions of the oblique grooves <NUM>. The vertical groove portions <NUM> configured as such utilize the rotation of the tire to provide excellent drainage performance and help to improve the wet performance.

As shown in <FIG>, in each of the oblique grooves <NUM>, each of the vertical groove portions <NUM> has a length L4 of <NUM>% or more and <NUM>% or less of a total length of the oblique groove <NUM>. The vertical groove portions <NUM> configured as such can decrease the rolling resistance while maintaining the cornering performance. The total lengths of the oblique grooves <NUM> and the lengths L4 of the vertical groove portions <NUM> each mean a so-called periphery length along the groove centerline. The same applies to the lengths of various parts described below.

The vertical groove portions <NUM> may be disposed on the tire equator (C) side of the first outer edge (5e1) of the central region <NUM>, on the first tread edge T1 side of the first outer edge (5e1), or on the first outer edge (5e1) as long as the minimum distance L1 is in the above range. As a preferred aspect, the vertical groove portions <NUM> are located on the tire equator (C) side of the first outer edge (5e1). It is preferred that the minimum distance L1 (shown in <FIG>) between each of the vertical groove portions <NUM> and the first outer edge (5e1) is <NUM>% or less of the maximum width W1 of the central region <NUM>. As a result, the above-described effects are reliably exerted.

As shown in <FIG>, in at least one pair of the oblique grooves <NUM> adjacent to each other in the tire circumferential direction among the plurality of the oblique grooves <NUM>, it is preferred that the vertical groove portions <NUM> are arranged at different positions from each other in the tire axial direction. As a result, the transient characteristics of the response when leaning over the vehicle become linear (hereinafter this action may be referred to as "improving the transient characteristics"), and excellent cornering performance is obtained.

The oblique grooves <NUM> include first oblique grooves <NUM> and second oblique grooves <NUM> having different angles of the vertical groove portion <NUM>. The angle α of the vertical groove portion <NUM> of each of the first oblique grooves <NUM> is less than <NUM> degrees. The angle α of the vertical groove portion <NUM> of each of the second oblique grooves <NUM> is <NUM> degrees or more. As a result, pitch sounds generated by the oblique grooves <NUM> are turned into white noise, therefore, noise performance can be improved. It should be noted that the oblique groove <NUM> shown in <FIG> is the first oblique groove <NUM>.

It is preferred that the number of the first oblique grooves <NUM> is greater than the number of the second oblique grooves <NUM> over the entire circumference of the tire. As a result, the effect of reducing the rolling resistance is reliably exerted while improving the noise performance.

As shown in <FIG>, each of the oblique grooves <NUM> includes an inner groove portion <NUM>. The inner groove portion <NUM> is arranged axially inside the vertical groove portion <NUM> in each of the oblique grooves <NUM>. The inner groove portion <NUM> is continuous with the vertical groove portion <NUM> via one of the bent portions <NUM> and extends linearly while being inclined with respect to the tire circumferential direction. It is preferred that a maximum angle β of the inner groove portion <NUM> with respect to the tire circumferential direction is larger than the angle α of the vertical groove portion <NUM>. Specifically, the angle β is from <NUM> to <NUM> degrees. The inner groove portions <NUM> configured as such can provide drainage capacity while maintaining rigidity in the tire axial direction of the central region <NUM>.

It is preferred that the inner groove portion <NUM> has a length greater than the length L4 of the vertical groove portion <NUM> (shown in <FIG>). Specifically, in each of the oblique grooves <NUM>, the length of the inner groove portion <NUM> is from <NUM>% to <NUM>% of a total length of the oblique groove <NUM>. The inner groove portions <NUM> configured as such helps to improve steering stability and the wet performance in a good balance.

Each of the oblique grooves <NUM> includes an outer groove portion <NUM>. The outer groove portion <NUM> is positioned axially outside the vertical groove portion <NUM> in each of the oblique grooves <NUM>. In the oblique groove <NUM> shown in <FIG>, the outer groove portion <NUM> extends linearly over a length thereof. The outer groove portion <NUM> has a length greater than the length L4 of the vertical groove portion <NUM> (shown in <FIG>). In each of the oblique grooves <NUM>, the length of the outer groove portion <NUM> is from <NUM>% to <NUM>% of the total length of the oblique groove <NUM>. The outer groove portions <NUM> configured as such can improve the wet performance during cornering.

<FIG> shows an enlarged view of one of the oblique grooves <NUM> which is different from the one shown in <FIG>. The oblique groove <NUM> shown in <FIG> is the second oblique groove <NUM>. As shown in <FIG>, each of the outer groove portions <NUM> is not limited to one extending linearly, but may extend in a zigzag shape, for example. The outer groove portions <NUM> configured as such can provide frictional force in multiple directions by groove edges thereof, therefore, the transient characteristics during cornering can be improved.

As shown in <FIG>, the tread portion <NUM> is provided with a plurality of the oblique grooves <NUM> with the outer groove portions <NUM> extending linearly, and a plurality of the oblique grooves <NUM> with the outer groove portions <NUM> extending in a zigzag shape. The arrangement of the oblique grooves <NUM> configured as such helps to improve the transient characteristics during cornering and the wet performance in a good balance.

<FIG> shows a B-B cross sectional view of <FIG>. As shown in <FIG>, each of the oblique grooves <NUM> has a pair of the groove edges (10e). Further, of the pair of the groove edges (10e) of each of the oblique grooves <NUM>, a chamfered portion <NUM> is formed on the groove edge (10e) on the toe side in the rotational direction (R). The chamfered portion <NUM> includes a sloping surface (20a) extending obliquely between one of groove walls of the oblique groove <NUM> and the ground contact surface. On the other hand, the groove edge (10e) on the heel side in the rotational direction (R) is not provided with a chamfered portion. As a result, excessive deformation of the land pieces divided by the oblique grooves <NUM> is suppressed, thereby, the rolling resistance is further decreased.

As shown in <FIG>, the tread portion <NUM> has a land ratio from <NUM>% to <NUM>%, for example. The tread portion <NUM> configured as such helps to improve the wet performance and the anti-wear performance in a good balance. It should be noted the land ratio is the ratio of the area of the actual ground contact surface (<NUM>) to the area of the virtual ground contact surface in which all the grooves provided in the tread portion <NUM> are filled.

While detailed description has been made of the motorcycle tire according to an embodiment of the present invention, the present invention can be embodied in various forms within the scope of the appended claims.

Motorcycle tires of size <NUM>/<NUM>-<NUM> having the basic structure of <FIG> and the tread pattern of <FIG> were made by way of test. Further, as a Reference, motorcycle tires having the basic structure shown in <FIG> and the tread pattern shown in <FIG> were made by way of test. As shown in <FIG>, the tread portion of the tires in the Reference are provided with a plurality of oblique grooves (a) without vertical groove portions. The rolling resistance was measured for these tires. The mounting rim, the inner pressure, and the measurement methods are as follows.

The tires in the Reference and Examples were run on a rolling resistance tester under the following conditions, and their rolling resistance was measured. The results are indicated by an index based on the rolling resistance of the Reference being <NUM>, wherein the larger the numerical value, the smaller the rolling resistance is, which is better.

Claim 1:
A motorcycle tire (<NUM>) comprising a tread portion (<NUM>), wherein
the tread portion (<NUM>) includes a first tread edge (T1), a second tread edge (T2), and a ground contact surface (<NUM>) defined between the first tread edge (T1) and the second tread edge (T2),
the ground contact surface (<NUM>) is curved in an arc shape so as to be convex outward in a tire radial direction,
the ground contact surface (<NUM>) includes a central region (<NUM>) and a first outer region (<NUM>),
the central region (<NUM>) is configured to contact a ground during straight running with zero camber angle, and includes a first outer edge (5e1) in a tire axial direction located on the first tread edge (T1) side and a second outer edge (5e2) in the tire axial direction located on the second tread edge (T2) side,
the first outer region (<NUM>) is defined on the first tread edge (T1) side of the first outer edge (5e1) of the central region (<NUM>),
the ground contact (<NUM>) surface is provided with a plurality of oblique grooves (<NUM>) each including a portion inclined with respect to a tire circumferential direction,
each of the oblique grooves (<NUM>) extends across the central region (<NUM>) and the first outer region (<NUM>),
each of the oblique grooves (<NUM>) includes a vertical groove portion (<NUM>) extending at an angle α of <NUM> degrees or less with respect to the tire circumferential direction,
a minimum distance (L1) in the tire axial direction along the ground contact surface (<NUM>) between the vertical groove portion (<NUM>) and the first outer edge (5e1) of the central region (<NUM>) is <NUM>% or less of a maximum width (W1) in the tire axial direction of the central region (<NUM>) along the ground contact surface (<NUM>), and
each of the oblique grooves (<NUM>) includes a pair of groove edges (<NUM>0e),
characterized in that
the motorcycle tire (<NUM>) is bound with an intended tire rotational direction, and
in the pair of the groove edges (10e), the groove edge on a toe side in the tire rotational direction is formed with a chamfered portion (<NUM>).