Patent ID: 12208647

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure is suitably applied to a tire for motorcycles, but may be applied to tires for passenger cars, heavy duty vehicles and the like.

Further, the present disclosure can be applied to not only pneumatic tires but also non-pneumatic tires so called airless tires.

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

FIG.1is a cross-sectional partial view of a pneumatic tire1for running on rough terrain as an embodiment of the present disclosure.

This cross-sectional view is a tire meridian cross-sectional view including the tire rotation axis (not shown) under a normal state of the pneumatic tire1.

FIG.2is a developed partial view of the tread portion2of the pneumatic tire1.

In the case of a pneumatic tire, the normal state is such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load. In this application including specification and claims, various dimensions, positions and the like of a pneumatic tire refer to those under the normal state of the tire unless otherwise noted.

The standard wheel rim is a wheel rim officially approved or recommended for the tire by standards organizations, i.e. JATMA (Japan and Asia), T&RA (North America), ETRTO (Europe), TRAA (Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC (India) and the like which are effective in the area where the tire is manufactured, sold or used.
The standard pressure is the air pressure for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list, i.e. the “maximum air pressure” in JATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given in the “Tire Load Limits at Various Cold Inflation Pressures” table in TRA or the like.

In the tire meridian cross-section of the tire1, the radially outer surface of the tread portion2is curved in an arc shape which is convex toward the outside in the tire radial direction.

The tread portion2is provided with a directional tread pattern for which the tire rotation direction N is specified.

The tread portion2in the present embodiment is provided with a plurality of crown blocks5disposed on the tire equator C.

Each of the crown blocks5comprises a crown block main portion10and crown fin portions11.

The crown block main portion10is formed in a V-shape bent convexly toward a tire circumferential direction opposite to the intended tire rotation direction N, namely, toward the toe side in the intended tire rotation direction N.

The crown fin portions11protrude from the crown block main portion10toward the toe side in the intended tire rotation direction N.

In such crown block5, the crown fin portions11suppress the crown block main portion10from collapsing toward the circumferential direction opposite to the intended tire rotation direction N, and the crown block main portion10exerts an essential mud digging power to improve the traction performance of the tire.

For each of the crown blocks5, only two crown fin portions11are formed. Thereby, the region where mud is easily clogged, that is, the region between the crown fin portions11becomes one place for each crown block5, and the clogging of mud is reduced. As a result, the crown block main portion10can exert its edge effect at a high level.

The tread portion2in this example is further provided with middle blocks6located axially outside the crown blocks5, and shoulder blocks7located axially outside the middle blocks6.

In the present embodiment, as shown inFIG.4, on each side in the tire axial direction of each of the crown blocks5, one middle block6is disposed adjacently. But, the blocks5to7are separated from each other by a tread base portion2R.

FIG.3is an enlarged top view of the crown block5.

As shown inFIG.3, the crown block main portion10has

a ground contacting top surface12,a heel-side block edge13, namely, the edge of the ground contacting top surface12on the heel side in the intended tire rotation direction N,a toe-side block edge14, namely, the edge of the ground contacting top surface12on the toe side in the intended tire rotation direction N, anda pair of circumferential edges15extending in the tire circumferential direction from the axially outer ends of the heel-side block edge13to the axially outer ends of the toe-side block edge14.
Further, the crown block main portion10has a block side wall surface8extending from the heel-side block edge13, the toe-side block edge14and the circumferential edges15to the above-mentioned tread base portion2R.
Each of the circumferential edges15in this example extends straight and substantially parallel to the tire circumferential direction.
Here, the expression “substantially parallel to the tire circumferential direction” means that the inclination angle with respect to the tire circumferential direction is in a range from 0 to 10 degrees.

In the present embodiment, each of the heel-side block edge13and the toe-side block edge14is inclined to the heel side in the intended tire rotation direction N toward both outer sides in a block width direction in parallel to the tire axial direction from the center in the block width direction.

The heel-side block edge13has the toe-side end13epositioned on the most toe-side in the intended tire rotation direction N.

The toe-side block edge14has the toe-side end14epositioned on the most toe-side in the intended tire rotation direction N.

The toe-side ends13eand14ein the present embodiment are located on the tire equator C.

The angle θ1of the heel-side block edge13is preferably not less than 10 degrees, more preferably not less than 15 degrees, but preferably not more than 45 degrees, more preferably not more than 35 degrees with respect to the tire axial direction. Here, the angle θ1is that of a straight line drawn between the toe-side end13eand the intersecting point between the heel-side block edge13and one of the circumferential edges15.

As shown inFIG.4, the heel-side block edge13is inclined with respect to the tire axial direction continuously from each circumferential edge15to the toe-side end13eto the same direction toward the toe side in the intended tire rotation direction N.

The heel-side block edge13comprisestwo first outer portions13aextending from the respective circumferential edges15,a first inner portion13bincluding the toe-side end13e, andtwo first intermediate portions13cconnecting between the first inner portion13band the two first outer portion13a.
The first intermediate portions13care inclined at a larger angle with respect to the tire axial direction than the first outer portions13aand the first inner portion13b.
In the present embodiment, each of the first outer portions13aand the first intermediate portions13cextends in a straight line, andthe first inner portion13bextends in a V shape.

The difference (θ1c−θ1a) between the angle θ1aof the first outer portion13aand the angle θ1cof the first intermediate portion13c, each with respect to the tire axial direction, is preferably not less than 10 degrees, more preferably not less than 15 degrees, but preferably not more than 35 degrees, more preferably not more than 30 degrees.

The difference (θ1c−θ1b) between the angle θ1bof the first inner portion13band the angle θ1cof the first intermediate portion13c, each with respect to the tire axial direction, is preferably not less than 10 degrees, more preferably not less than 15 degrees, but preferably not more than 35 degrees, more preferably not more than 30 degrees.

The toe-side block edge14comprises an inner edge portion14A and two outer edge portions14B.

The inner edge portion14A extends axially inwardly from connection portions K between the crown block main portion10and the two crown fin portions11.

The two outer edge portions14B respectively extend axially outwardly from connection portions K between the crown block main portion10and the two crown fin portions11.

The inner edge portion14A includes the toe-side end14e.

The inner edge portion14A extends in a V shape.

In the present embodiment, the outer edge portions14B respectively extend to the circumferential edges15.

In the present embodiment, each of the outer edge portions14B extends in a straight line.

In the present embodiment, each of the two crown fin portions11is formed in a parallel quadrilateral shape in the top view of the block.

As shown inFIG.4, the crown fin portions11in this example each have

an outer edge11ein the block width direction,an inner edge11iin the block width direction,a heel-side edge11aon the heel side in the intended tire rotation direction N, anda toe-side edge11bon the toe side in the intended tire rotation direction N.
The outer edge11eand the inner edge11iin this example extend in parallel with the tire circumferential direction.
The first edge11aand the second edge11bin this example extend in parallel with the adjacent outer edge portion14B.
The inner edge11i, the outer edge11e, the heel-side edge11aand the toe-side edge11bdefine the radially outer surface11A of the crown fin portion11.

As shown inFIG.6, in the present embodiment, the radially outer surface11A is located radially outside the ground contacting top surface12of the crown block main portion10. However, the radially outer surface11A may be located at the same radial position as the ground contacting top surface12of the crown block main portion10.

The outer edges11eof the two crown fin portions11are located inside in the block width direction than the both ends10ein the tire axial direction of the crown block main portion10. As a result, the deformation of the crown fin portions11is ensured, and the effect of ejecting mud is enhanced.

The distance La in the tire axial direction between the two crown fin portions11is preferably set in a range of not less than 30%, more preferably not less than 35%, but not more than 50%, more preferably not more than 45% of the width W1in the tire axial direction of the crown block main portion10as shown inFIG.3.

Since the distance La is not less than 30% of the width W1, mud ejection becomes smooth. Since the distance La is not more than 50% of the width W1, the collapse of the crown block main portion10can be effectively suppressed.

The distance Lb in the tire axial direction between the outer edge11eof each crown fin portion11and the adjacent axial end10eof the crown block main portion10is preferably not less than 15%, more preferably not less than 20%, but preferably not more than 35%, more preferably not more than 30% of the width W1in the tire axial direction of the crown block main portion10. As a result, the deformation of the crown fin portions11is ensured, and the effect of ejecting mud is enhanced.

The width W2in the tire axial direction of each crown fin portion11is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 20%, more preferably not more than 15% of the width W1in the tire axial direction of the crown block main portion10.

Since the width W2is not less than 5% of the width W1, it is possible to effectively suppress the collapse of the crown block main portion10.

Since the width W2is not more than 20% of the width W1, excessive increase in the rigidity of the crown fin portion11is suppressed, and the effect of ejecting mud is maintained.

In order to prevent the crown block main portion10from collapsing, the protruding length Lc (shown inFIG.3) in the tire circumferential direction of each crown fin portion11from the crown block main portion10is preferably not less than 50%, more preferably not less than 60% of the length L1(shown inFIG.3) in the tire circumferential direction of the crown block main portion10.

However, if the protruding length Lc is excessively large, the effect of ejecting mud may deteriorate, therefore, the protruding length Lc is preferably not more than 150%, more preferably not more than 110% of the length L1.

As shown inFIG.5, the connection portion K between the crown block main portion10and each crown fin portion11is provided with a shallow groove18for promoting deformation of a part of the crown fin portion11on the connection portion K side. Thus, such shallow grooves18help to smoothly eject the mud clogged between the crown fin portions11.

The shallow groove18extends from the inner edge portion14A to the outer edge portion14B so as to surround the above-said part of the crown fin portion11on the connection portion K side.

The shallow groove18extends along a part of the outer edge11e, the heel-side edge11a, and a part of the inner edge11i.

Thus, the shallow groove18extends in a U shape convex toward the heel side in the intended tire rotation direction N.

The shallow groove18allows the crown fin portion11to deform as if independent from the crown block main portion10, therefore, the traction performance on rough terrain is further improved.

FIG.6is a cross-sectional view taken along line A-A ofFIG.5.

As shown inFIG.6, the groove depth d1of the shallow groove18from the ground contacting top surface12of the crown block main portion10is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 25%, more preferably not more than 20% of the radial height H1of the crown block5from the tread base portion2R to the ground contacting top surface12.
Further, as shown inFIG.5, the width W3of the shallow groove18is preferably not less than 2%, more preferably not less than 5%, but preferably not more than 15%, more preferably not more than 10% of the width W1in the tire axial direction of the crown block main portion10.
As a result, the above-mentioned action is effectively exhibited, and the crown fin portions11and the crown block main portion10secure rigidity and generate a larger shearing force against mud and soil.

It is preferable that the distance Ld measured parallel to the tire circumferential direction from the heel-side end18eof the shallow groove18to the toe-side block edge14is not more than 60% of the length L1in the tire circumferential direction of the crown block main portion10.

Thereby, the rigidity in the tire circumferential direction of the crown block main portion10is maintained.

As a result, the effect of suppressing the collapse of the crown block5when contacting with the ground is highly exhibited.

The width W1in the tire axial direction of the crown block main portion10is preferably not less than 20%, more preferably not less than 25%, but preferably not more than 40%, more preferably not more than 35% of the developed tread width TW. As shown inFIG.2, the developed tread width TW is the distance measured in the tire axial direction between the tread edges Te when the tread portion2is unfolded flat.

FIG.7is a cross-sectional view taken along line B-B ofFIG.5.

As shown inFIG.7, the block side wall surface8of the crown block main portion10includes

a first side wall surface16extending radially inwardly from the heel-side block edge13, anda second side wall surface17extending radially inwardly from the toe-side block edge14.

The first side wall surface16comprises a radially outer portion16aand a radially inner portion16b.

In the cross-sectional view, the radially outer portion16aextends substantially straight, radially inwardly from the heel-side block edge13, while inclining toward the toe side in the intended tire rotation direction N with respect to a straight line drawn normally to the ground contacting top surface12from the heel-side block edge13.

Here, the expression “extend substantially straight” means to extend parallel to not only a perfect straight line having an infinite radius of curvature but also an arc line having a radius of curvature of at least 200 mm.

The radially inner portion16bextends from the radially outer portion16ato the tread base portion2R while curving in an arc shape in the cross-sectional view. Such first side wall surface16can deeply dig into mud or soft ground.

The radially inner portion16bis formed with a single radius of curvature in the present embodiment.

Such radially inner portion16brelaxes the stress concentration acting on the radially inner portion16b, and further improve the traction performance. However, the radially inner portion16bmay be formed by a multi-radius curve.

The second side wall surface17in the present embodiment comprises a first portion17a, a second portion17b, and a third portion17c.

The first portion17aextends radially inwardly from the toe-side block edge14.

The second portion17bextends radially inwardly from the first portion17aand is inclined more gently than the first portion17a.

The third portion17cextends radially inwardly from the second portion17bto the tread base portion2R.

In the present embodiment, each of the first portion17aand the second portion17bextends linearly in the cross-sectional view. And the third portion17cis curved in an arc shape.

For example, the third portion17cis formed in an arc shape concave toward the heel side in the intended tire rotation direction N.

FIG.8shows the vicinity of the middle block6.

As shown inFIG.8, each middle block6is inclined to the heel side in the intended tire rotation direction N, while extending from the inside to the outside in the tire axial direction, and comprises a middle block main portion20having a parallelogram shape, and a middle fin portion21protruding toward the toe side in the intended tire rotation direction N from the middle block main portion20.

The middle block main portion20has a ground contacting top surface22, a heel-side middle edge23, a toe-side middle edge24, and a pair of circumferential middle edges25extending from both ends of the heel-side middle edge23, respectively, toward the toe side in the intended tire rotation direction N.

The pair of circumferential middle edges25is an axially inner circumferential middle edge25aadjacent one of the crown blocks5, and an axially outer circumferential middle edge25badjacent to one of the shoulder blocks7.

The circumferential middle edges25in this example extend linearly.

In the present embodiment, the middle block main portion20is provided with the two middle fin portions21. The two middle fin portions21arean axially outer middle fin portion21A connected to the axially outer circumferential middle edge25b, andan axially inner middle fin portion21B located axially inside the axially outer middle fin portion21A.

The axially outer middle fin portion21A is directly connected to the middle block main portion20.

The axially outer edge26of the axially outer middle fin portion21A and the axially outer circumferential middle edge25bare formed by a single straight line.

The axially inner middle fin portion21B is connected to the middle block main portion20, and along the junction between them, a middle shallow groove30is formed. The axially inner edge27of the axially inner middle fin portion21B and the axially inner circumferential middle edge25aextend in line across the middle shallow groove30. Since the deformation of the axially inner middle fin portion21B is promoted by the middle shallow groove30, the mud clogged between the middle fin portions21can be smoothly ejected.

The middle shallow groove30's edge30apositioned on the heel side in the intended tire rotation direction N and extending in the longitudinal direction forms the above-mentioned toe-side middle edge24in this example.

The groove width W4of the middle shallow groove30is preferably not less than 80%, more preferably not less than 90%, but preferably not more than 125%, more preferably not more than 110% of the groove width W3(FIG.5) of the shallow groove18of the crown block5.

The groove depth of the middle shallow groove30(not shown) is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 20%, more preferably not more than 15% of the block height of the middle block main portion20measured from the ground contacting top surface to the tread base portion2R.
The axial width W5(FIG.8) of the middle block main portion20is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 25%, more preferably not more than 20% of the developed tread width TW.

FIG.9is a top view of one of the shoulder blocks7.

As shown, the shoulder block7in this example is formed in a generally quadrilateral shape, more specifically trapezoidal shape in its top view.

The ground contacting top surface7aof the shoulder block7has an axially outer edge41, an axially inner edge42, a toe-side edge43, and a heel-side edge44.

The axially outer edge41extends in the tire circumferential direction, and in this example, forms a part of the tread edge Te.

The axially inner edge42extends in the tire circumferential direction in this example.

The toe-side edge43extends in parallel with the tire axial direction from the axially outer edge41toward the axially inner edge42in this example.

The heel-side edge44extends from the axially inner edge42to the axially outer edge41while inclining with respect to the tire axial direction, for example, toward the intended tire rotation direction N in this example.

Each of the shoulder blocks7is provided with a shoulder shallow groove45in this example.

As shown inFIG.9, the shoulder shallow groove45extends in a V shape in the top view of the shoulder block7.

Such shoulder shallow groove45promotes the deformation of the shoulder block7, and helps to eject the mud clogged between the shoulder block7and the adjacent middle block6.

The shoulder shallow groove45is composed of a circumferential portion46extending in the tire circumferential direction, and an axial portion47extending in the tire axial direction.

The circumferential portion46extends at an angle of not more than 45 degrees with respect to the tire circumferential direction.

The axial portion47extends at an angle of more than 45 degrees with respect to the tire circumferential direction.

In this example, the circumferential portion46extends in parallel with the tire circumferential direction from the toe-side edge43toward the heel side in the intended tire rotation direction N, and ends within the shoulder block7.

In this example, the axial portion47extends from the axially inner edge42toward the outside in the tire axial direction, and is connected to the end of the circumferential portion46. The axial portion47extends in parallel with the heel-side edge44.

Such shoulder shallow groove45further promotes deformation of the shoulder block7.

The groove width W6of the shoulder shallow groove45is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 25%, more preferably not more than 20% of the axial width W7(FIG.9) of the shoulder block7. The groove depth of the shoulder shallow groove45is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 20%, more preferably not more than 15% of the block height of the shoulder block7measured from the ground contacting top surface to the tread base portion2R.

The axial width W7of the shoulder block7is preferably not less than 5%, more preferably not less than 7%, but preferably not more than 20%, more preferably not more than 15% of the developed tread width TW.

It is preferable that the tread rubber2G (FIG.1) by which the above-mentioned blocks5to7are formed has a rubber hardness of not less than 70 degrees, and not more than 90 degrees.

Here, the rubber hardness means the durometer A hardness measured at a temperature of 23 degrees C. according to the Japanese Industrial Standard (JIS) K6253.

While detailed description has been made of a preferable embodiment of the present disclosure, the present disclosure can be embodied in various forms without being limited to the illustrated embodiment.

Comparison Tests

Based on the tread pattern shown inFIG.2, pneumatic tires for a rear wheel of a motorcycle for running on rough terrain were experimentally manufactured as test tires (Working example tires Ex.1-Ex.6 and Comprehensive example tire Ref.1).

Specifications of the test tires are shown in Table 1.

The test tires were tested for the traction performance, braking performance and overall performance, using a 450 cc motorcycle for motocross competition having the following rim sizes and tire sizes.

front wheel rim size: 21×1.60rear wheel rim size: 19×2.15front tire size: 80/100-21rear tire size: 120/80-19
In the test, the rear tire was changed, but the front tire was not changed and an identical tire was used. (tire pressure: 80 kPa)
The test method was as follows.
<Traction Performance/Brake Performance/Overall Performance>

The traction performance, brake performance and overall performance when the above-mentioned motorcycle was run on rough terrain covered with mud were evaluated by the test rider.

Here, the “traction performance” is an evaluation of the traction force at the time of accelerating during straight running and cornering, made by the test rider.

The “brake performance” is an evaluation of the braking force at the time of braking during straight running and cornering, made by the test rider.

The “overall performance” is an evaluation of the running stability at the time of accelerating and braking during straight running and cornering, made by the test rider.

The test rider evaluated each performance on a ten-point scale, and the results are shown in Table 1.

TABLE 1Ref.Ex.Ex.Ex.Ex.Ex.Ex.Tire1123456number of crown fin3222222portions per blockangle θ1 (deg.)15.717.417.417.417.417.417.4La/W1 (%)30203838385045W2/W1 (%)12888888Lc/L1 (%)130969696969696(P)resence/(A)bsenceAPAPPPPof shallow grooved1/H1 (%)—10—10101010W3/W1 (%)—3—3333Ld/L1 (%)—38—38383838tread rubber70707070807070hardness (deg.)traction performance4.56.566.5766.5brake performance4.5666.5766overall performance4.56.566.5766.5

From the test results, it was confirmed that the traction performance and braking performance on rough terrain of the working example tires were improved as compared with the comparative example tire.

STATEMENT OF THE PRESENT DISCLOSURE

The present disclosure is as follows:—

Disclosure 1: A tire for running on rough terrain for which an intended tire rotational direction is specified, and which comprises a tread portion provided with crown blocks disposed on the tire equator, wherein

each of the crown blocks comprises
a V-shaped crown block main portion which bends convexly toward a circumferential direction opposite to the intended tire rotation direction, and
only two crown fin portions projecting from the crown block main portion toward the above-said circumferential direction opposite to the intended tire rotation direction.
Disclosure 2: The tire for running on rough terrain according to Disclosure 1, whereineach of said only two crown fin portions has an outer edge in a block width direction which is located inside in the block width direction than both axial ends of the crown block main portion.
Disclosure 3: The tire for running on rough terrain according to Disclosure 1 or 2, whereinthe distance in the tire axial direction between said only two crown fin portions is in a range from 30% to 50% of the width in the tire axial direction of the crown block main portion.
Disclosure 4: The tire for running on rough terrain according to Disclosure 1, 2 or 3, whereinthe width in the tire axial direction of each of said only two crown fin portions is in a range from 5% to 20% of the width in the tire axial direction of the crown block main portion.
Disclosure 5: The tire for running on rough terrain according to Disclosure 1, 2, 3 or 4, whereinthe protruding length of each of said only two crown fin portions measured in the tire circumferential direction from the crown block main portion is not less than 50% of the length in the tire circumferential direction of the crown block main portion
Disclosure 6: The tire for running on rough terrain according to Disclosure 1, 2, 3, 4 or 5, whereina connection portion K between the crown block main portion and each of the crown fin portions is provided with a shallow groove for promoting deformation of a part of the crown fin portion on the connection portion side.
Disclosure 7: The tire for running on rough terrain according to Disclosure 6, whereinthe crown block main portion has a ground contacting top surface and a toe-side block edge,the toe-side block edge comprises
an inner edge portion extending inward in the tire axial direction from the connection portion, and
an outer edge portion extending outward in the tire axial direction from the connection portion, andthe shallow groove extends from the inner edge portion to the outer edge portion so as to surround said part of the crown fin portion on the connection portion side.
Disclosure 8: The tire for running on rough terrain according to Disclosure 6 or 7, whereinthe depth of the shallow groove is in a range from 5% to 25% of the radial height of the crown block main portion.
Disclosure 9: The tire for running on rough terrain according to any one of Disclosures 6 to 8, whereinthe width of the shallow groove is in a range from 2% to 15% of the width in the tire axial direction of the crown block main portion.
Disclosure 10: The tire for running on rough terrain according to any one of Disclosures 6 to 9, whereinthe crown block main portion has a ground contacting top surface and a toe-side block edge, andthe distance in the tire circumferential direction between the toe-side block edge and a heel-side end of the shallow groove is not more than 60% of the length in the tire circumferential direction of the crown block main portion.
Disclosure 11: The tire for running on rough terrain according to any one of Disclosures 1 to 10, whereinthe crown block main portion has a heel-side block edge, andthe angle of the heel-side block edge with respect to the tire axial direction is in a range from 10 to 45 degrees.

DESCRIPTION OF THE REFERENCE SIGNS

1tire for running on rough terrain2tread portion5crown block10crown block main portion11crown fin portionN intended tire rotational direction