JPH11129706A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wet grip shortage in the initial period to middle period of wear caused by over curing of tread rubber, to stably develop the wet grip performance over the whole using period, and to suppress a drop in driving.braking capability in a rough ground. SOLUTION: A lateral groove Y extending from a tread edge Te in almost the tire axial direction and a longitudinal groove G connecting the lateral groove Y in a tire equator vicinity Qc are formed on a tread surface 2S. The longitudinal groove G consists of a crossing part with the lateral groove Y and a main part between the crossing parts, and the groove depth of the main part is formed 30-60% of the groove depth Hy of the lateral groove Y. The lateral groove Y on a tread surface 2Sa where the main part disappears of the longitudinal groove G caused by advancing wear consists of a lateral groove main remaining part where the groove width is constantly or gradually decreasingly extends toward a tire equator C from the tread edge Te and a lateral groove wide width remaining part continuing to the inner end of the lateral groove main remaining part and having the groove width wider than the groove width at the inner end.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic tire which can improve the shortage of wet grip during the initial to middle stages of wear and is particularly suitable for construction vehicles such as dump trucks.

[0002]

2. Description of the Related Art A heavy-duty pneumatic tire used for construction vehicles such as dump trucks, which is used on uneven terrain such as earth roads, is mainly used on uneven terrain. In order to secure the driving and braking performance in
As shown in FIG. 6, a lug pattern in which a long lug groove a (lateral groove) of a super deep groove type extending from the tread edge Te to the vicinity of the tire equator C is frequently used.

However, in this type of tire, since the tread rubber is formed thick, the vulcanization to the inside of the tread results in excessive vulcanization (over vulcanization) of the tread surface, and the tire has a high strength, an elastic modulus and the like. A phenomenon called reversion that greatly reduces rubber properties occurs. As a result, after the middle period of wear when the over-vulcanized rubber wears out, the rubber portion of the desired physical properties is grounded, so that sufficient drive and braking properties are exhibited, but the initial stage of wear when the over-vulcanized rubber is grounded. In particular, iron roads on good roads and work sites, especially in rainy weather,
When running on the cover of a groove, etc., the wet grip performance was insufficient, such as inducing a slip. This tendency is more remarkable when a natural rubber excellent in abrasion resistance and low heat generation is used for the tread rubber.

Therefore, the present inventors formed a shallow vertical groove b on the lug pattern as shown by the dashed line in FIG. 6 and drained only in the initial to middle wear periods in which the super-vulcanized rubber remained. The idea was to make it more responsive and compensate for the lack of wet grip.

However, since the vertical groove b reduces the horizontal edge component in the lug groove a, the vertical groove b is used for driving on uneven terrain.
It becomes a factor of the decrease in braking performance, and in the early to middle stages of wear,
Although the lug groove a can exhibit a sufficiently deep and high driving / braking property, the driving / braking performance of the tire as a whole tends to decrease. Also, after the middle wear period when the lug groove depth is halved,
Although the drive / braking performance is reduced by the disappearance of the flutes b and the puncture resistance is maintained, the drainage performance changes before and after the flute b disappears. The problem has to be found.

Accordingly, the present invention provides a tire having a shallow vertical groove formed on the lug pattern, wherein the lug groove (lateral groove) on the tread surface when the vertical groove disappears has a constant groove width from the tread edge. Or, to improve the shortage of wet grip in the initial to middle stages of wear, based on the fact that the inner end of the horizontal groove main remaining part that gradually decreases and has a groove width wider than the inner end of the horizontal groove main remaining part is provided. It is another object of the present invention to provide a heavy-duty pneumatic tire capable of suppressing a decrease in driving / braking performance due to the formation of the vertical groove and reducing a change in drainage performance before and after the disappearance of the vertical groove.

[0007]

In order to achieve the above-mentioned object, a heavy-duty pneumatic tire according to the present invention is provided on a tread surface with an opening at a tread edge and extending substantially in the tire axial direction, and having a circumferential interval. In addition to providing a separated horizontal groove and a vertical groove connecting the horizontal groove near the tire equator and extending in the circumferential direction, the vertical groove includes an intersection that intersects the horizontal groove and a main portion between the intersections, and By setting the groove depth of the main portion to 30 to 60% of the groove depth of the horizontal groove, the horizontal groove on the tread surface in which the main portion of the vertical groove has disappeared due to the progress of wear extends from the tread edge and has a groove width. From the main transverse groove remaining portion that is constant or gradually reduced toward the tire equator, and from the transverse groove wide remaining portion that is continuous at the inner end of the transverse groove main remaining portion on the tire equator side and the groove width is larger than the inner end of the transverse groove main remaining portion. Is characterized by becoming It is proposed.

The position P0 at which the groove cross-sectional area in the remaining portion of the wide groove is maximum is provided within a range of 10 to 22% of the tread width from the equator of the tire. A large-capacity portion having a groove cross-sectional area larger than the groove cross-sectional area at the inner end of the tread, and the circumferential length of the large-capacity portion is set to 5 to 10% of the tread width. It is preferable to enhance the effect of suppressing the decrease and the effect of reducing the change in drainage performance.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a heavy-load pneumatic tire 1 (hereinafter referred to as a tire 1) includes a tread portion 2.
And sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and bead portions 4 located at radially inner ends of the respective sidewall portions 3 in the tire radial direction. It is formed as an ultra deep groove type dump truck tire.

A carcass 6 is bridged between the bead portions 4 and 4 on the tire 1, and a belt layer 7 is wound around the carcass 6 and in the tread portion 2 in the circumferential direction.

The carcass 6 is formed from one or more carcass plies in which carcass cords are arranged at a cord angle of 70 to 90 ° with respect to the tire equator C, and each carcass ply is formed from the tread portion 2 to the sidewall portion. 3, the bead portion 4 is folded inward and outward around the bead core 5 of the bead portion 4 and locked. As the carcass cord, an organic fiber cord made of nylon, polyester, rayon, aromatic polyamide fiber or the like, or an inorganic fiber cord made of steel fiber or the like can be used.

In this embodiment, the carcass 6 is formed of one carcass ply 6A in which steel carcass cords are arranged at a cord angle of about 90 °. .

The belt layer 7 includes a plurality of belt plies,
In the present example, for example, 45 to 70 ° with respect to the tire equator C
The innermost first belt ply 7A inclined at an angle of about
And the second and third belt plies 7B and 7C in which the belt cord is inclined at a small angle of 10 to 25 degrees with respect to the tire equator C.
And a three-layer structure in which the belt cords are overlapped so that the belt cords cross each other between the plies.

As shown in FIG. 2, the tire 1 has, on a tread surface 2S, which is an outer surface of the tread portion 2, a plurality of lateral grooves Y opening at a tread edge Te and extending substantially in the tire axial direction. A pair of vertical grooves G, G that intersect with Y in the vicinity of the tire equator Qc and extend in the circumferential direction are provided.

Here, as shown in FIG. 1, the tread surface 2S has a convex curve such as an arc centered on the tire equatorial plane in a meridional section of the tire, and the tread edge Te
Is defined as the intersection of the tread surface 2S and the outer surface of the sidewall portion 3. In this example, in order to improve the wandering performance, the tread surface 2S has a tapered shoulder structure in which both end portions are formed by slopes. Therefore, the tread edge Te is defined by the intersection of the slope and the outer surface of the sidewall portion 3. Constitute. In addition, the tread portion 2 can adopt a round shoulder structure in which both end portions of the tread surface 2S are formed by an arc surface, in addition to the square shoulder structure in which the slope is removed. The tread edge Te is constituted by an intersection or a contact point with the outer surface of the sidewall portion.

The longitudinal groove G has a groove width Wg in the tire axial direction.
Is a zigzag groove having a width of at least 0.025 times the tread width TW, which is the width between the tread edges Te, Te, and in this example, about 0.072 times the tread width TW. % In the vicinity of the tire equator Qc which is a region separated by a distance of not more than%. Note that the vertical groove G may be a straight groove.

In the present embodiment, the horizontal grooves Y are circumferentially spaced at a pitch substantially equal to the zigzag pitch of the vertical grooves G. The lateral groove Y is a super-deep groove type lug-shaped groove extending substantially in the tire axial direction from an outer end Eo opened at the tread edge Te.
This vertical groove G is divided into an intersection 10 with the horizontal groove Y and a main portion 11 between the intersections 10 and 10.

The main portion 11 of the vertical groove G has a groove depth Hg of 0.30 to 0.6 of the groove depth Hy of the horizontal groove Y.
It has a shallow depth of 0 times, so that the main portion 11 can disappear after the middle stage of wear. The groove width Wg of the vertical groove G
Is less than 0.025 TW, the replenishment of the wet grip performance becomes insufficient, and if it exceeds 0.10 TW, the drive / braking performance is remarkably reduced, which is not preferable. On the other hand, when the groove depth Hg is less than 0.30 Hy, the longitudinal groove G may be lost earlier than the super-vulcanized rubber, and after the middle period of wear when the groove volume of the lateral groove Y is reduced by half, the longitudinal groove G When the groove depth Hg is greater than 0.60 Hy, the driving / braking performance is greatly reduced. Therefore, it is preferable that the groove depth Hg be 0.30 Hy to 0.50 Hy.

Here, as shown in FIG. 1, the lateral groove Y has a substantially constant depth over a range of at least 40% or more of the lateral groove length Ly in the tire axial direction. And the lateral groove Y has a depth of the constant depth region 12.
Is defined as the groove depth Hy. This groove depth Hy is 15m
m, and in this example, 20.0 to 23.0 mm.

In the lateral groove Y, the angle α of the center of the groove width with respect to the tire axial direction is set to 10 degrees or less, preferably 5 degrees or less, thereby ensuring the driving and braking performance on uneven terrain. The lateral groove Y may be formed in a straight line, but may be formed in a curved line or a broken line. At this time, the angle α of a straight line connecting the center of the groove width at the outer end Eo and the inner end Ei is set in the above range. And

In the present embodiment, the inner end Ei of the lateral groove Y terminates at a position beyond the vertical groove G and a distance from the tire equator C.
A rib-shaped land portion 1 extending continuously between the inner ends Ei in the circumferential direction.
By forming 3, smooth rolling properties are maintained. Therefore, the distance L of the inner end Ei from the tire equator C is
1 is preferably 4% or more of the tread width TW for smooth rolling properties.

Further, the main portion 11 of the vertical groove Y is formed by the progress of wear.
In the worn tread surface 2Sa in which the groove has disappeared, the lateral groove Y extends from the tread edge Te toward the tire equator C while the groove width in the tire circumferential direction is constant or gradually reduced as shown in FIGS. It is formed of a main remaining portion 15 and a wide groove wide width remaining portion 16 that is continuous with the inner end 15 e of the horizontal groove main remaining portion 15. In FIG. 4, in order to explain the lateral groove Y, the groove volume portion is shown in a block shape on the contrary.

This wide groove wide remaining portion 16 is made up of the horizontal groove main remaining portion 15.
Is a wide portion having a groove width W2 larger than the groove width W1 at the inner end 15e. As shown in FIGS. 5A and 5B, the lug groove a of the conventional lug pattern has a groove width from the outer end ao to the inner end ai on both the new tread surface and the worn tread surface. Has a constant or gradually decreasing profile toward the tire equator C, and is therefore largely different from the present invention in the lateral groove wide width remaining portion 16.

As shown in FIG. 4, the wide groove wide remaining portion 16 has a groove cross-sectional area position P0 at which the groove cross-sectional area becomes a maximum value S0 in a plane parallel to the tire equatorial plane CO. The distance L3 of P0 from the tire equator C is in the range of 10 to 22% of the tread width TW. In this example, the groove cross-sectional area position P0 coincides with the position Pm of the maximum value W2m of the groove width W2 of the horizontal groove wide width remaining portion 16. Note that the lateral groove Y
Is a variable depth region 1 in which the groove depth is gradually reduced from the constant depth region 12 toward the inner end Ei, for example, in a stepped manner.
Therefore, depending on the change of the groove depth, the position P0 of the groove cross-sectional area may be different from the position Pm of the maximum groove width.

It should be noted that the horizontal groove wide width remaining portion 16 is
Are formed in the change depth region 17 so as to substantially overlap with the intersections 10.

The wide-width-remaining portion 16 of the lateral groove is the same as the main-remaining portion 1 of the lateral groove.
5 has a large volume portion 16A having a groove cross section larger than the groove cross section S1 at the inner end 15e of the inner end 15e.
The circumferential length L2 of 6A is 5 to 5 of the tread width TW.
10% and the maximum value S0 of the groove cross-sectional area is increased to 1.5 to 1.8 times the groove cross-sectional area S1 at the inner end 15e.

As described above, the provision of the wide groove wide width portion 16 having a groove width of W2> W1 enhances drainage when the vertical groove G disappears, reduces the degree of change in wet grip performance, and reduces wear from the beginning to the end of wear. And stable wet grip performance can be achieved. In particular, the large volume portion 16A has a length L2.
, The effect of improving drainage can be more reliably and effectively exerted. In addition, before the disappearance of the vertical groove G, the horizontal groove wide width portion 16 enhances the driving / braking property particularly by increasing the groove volume, and can offset the adverse effect on the driving / braking property caused by the formation of the vertical groove G. In particular, the remaining width of the wide groove 16
Is preferably formed so as to overlap with the intersection 10 of the vertical groove G in order to perform the above-mentioned cancellation in a well-balanced manner.

The distance L3 at the groove cross-sectional area position P0 is:
When the tread width is less than 10% of the TW and the large volume portion 16
When the length L2 of A exceeds 10% of the tread width TW, the rigidity of the rib-shaped land portion 13 is locally reduced, which causes uneven wear and lowers rolling performance. Conversely, when the distance L3 exceeds 22% of the tread width TW, and when the length L2 is less than 5% of the tread width TW, the contact pressure at the groove cross-sectional area position P0 decreases and the groove volume itself decreases. Since the increase is insufficient, the effects on drainage and driving / braking tend to be insufficient.

When the maximum value S0 of the groove cross-sectional area is less than 1.5 times the groove cross-sectional area S1, the effects on drainage and driving / braking tend to be insufficient, and conversely, when the value exceeds 1.8 times. This causes problems such as uneven wear.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The tire having the structure shown in FIG.
A 22.5 dump truck tire was prototyped based on the specifications in Table 1, and the prototype tire was tested for wear resistance, wet grip performance, wet turning performance, and driving and braking performance on uneven terrain. Each of the test tires has the same configuration except for the tread pattern.

Each test method is as follows. Wear resistance Each new test tire was used with a rim (7.50 × 22.
5) Under the condition of internal pressure (8.0 kgf / cm ² ), it was mounted on the driving wheel of a dump vehicle, and when it traveled a distance of 20,000 km on a test course (dry road surface), the amount of wear was measured and the reciprocal thereof was calculated. The comparison was made using an index with the comparative example as 100. The higher the value, the better. Wet grip performance When new, mid-wear when vertical grooves disappear, and horizontal groove balance 1.
Using each of the test tires at the wear limit of 6 mm, with the constant load (10 tons) loaded on the dump vehicle, a time trial run was performed on the wet circuit surface with a depth of 3 mm at the limit travel speed at that time. The reciprocal of the running time was compared with an index when the tire of Comparative Example 1 was 100 when the tire was new. The higher the value, the better. Wet turning performance Using new test tires, medium wear, and wear limit tires, with a constant load (10 tons) loaded on the dump vehicle, a water depth of 3 m on an asphalt road surface with a radius of 100 m
m, the vehicle is approached on a course provided with a puddle having a length of 20 m while gradually increasing the speed, the lateral acceleration (lateral G) is measured, and the average lateral G of the front wheels at a speed of 60 km / h is calculated. Calculated. The results were compared by an index with the tire of Comparative Example 1 being 100 when new. The higher the value, the better.

Driving / braking performance on uneven terrain Using the test tires at the time of new, middle wear, and wear limit, the dump vehicle was loaded with a constant load (10 tons), and the terrain (diameter 2 to 2) was loaded. Road surface covered with 3cm gravel)
At a speed of 60 km / h, and measure the braking distance. The reciprocal of the braking distance at that time was compared with an index when the tire of Comparative Example 1 was 100 when the tire was new. The higher the value, the better.

[0033]

[Table 1]

As shown in Table 1, it can be confirmed that it is possible to improve the shortage of the wet grip from the time of a new article (early wear) to the middle of wear, and also to suppress the reduction of the driving / braking property due to the formation of the longitudinal groove. .

[0035]

Since the present invention is configured as described above,
Improves shortage of wet grip in the early to middle wear due to over-vulcanization of tread rubber, stabilizes wet grip performance over the entire service period, and reduces drive and braking performance on uneven terrain. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tire according to an embodiment of the present invention.

FIG. 2 is a plan view showing the tread pattern.

FIG. 3 is a plan view showing a horizontal groove when a vertical groove disappears.

FIG. 4 is a perspective view showing a horizontal groove when a vertical groove disappears.

FIGS. 5A and 5B are plan views showing examples of tread patterns of tires used in Comparative Examples in Table 1. FIGS.

FIG. 6 is a diagram illustrating a conventional technique.

[Explanation of symbols]

 2S Tread surface 10 Intersection 11 Main part 15 Main part of horizontal groove 15e Inner end of main part of horizontal groove 16 Horizontal groove wide remaining part 16A Large volume G Vertical groove Hg Groove depth of main part Hy Horizontal groove depth L3 Periphery of large volume Length in the direction Qc Near the tire equator S0 Maximum value of groove cross-sectional area at the remaining wide part of the lateral groove S1 Groove cross-sectional area at the inner end of the main remaining part of the lateral groove Te Tread edge Y Lateral groove

Claims (3)

[Claims] 1. A tread surface is provided with a lateral groove which is open at a tread edge and extends substantially in the tire axial direction and is circumferentially spaced apart from each other, and a longitudinal groove which connects the lateral grooves near the tire equator and extends in a circumferential direction. In addition, the vertical groove includes an intersection portion intersecting with the horizontal groove and a main portion between the intersection portions, and the groove depth of the main portion is 30 to 60% of the groove depth of the horizontal groove.
By doing so, the horizontal groove on the tread surface where the main part of the vertical groove has disappeared due to the progress of wear, the horizontal groove main residual part extending from the tread edge and the groove width is constant or gradually decreasing toward the tire equator, and the horizontal groove main residual part A heavy-load pneumatic tire, comprising: a lateral groove wide width remaining portion which is continuous at an inner end on the tire equator side and has a groove width larger than an inner end of the lateral groove main remaining portion. 2. The position of the lateral groove on the tread surface where the main portion has disappeared is set at a position P0 where the groove cross-sectional area in the remaining wide part of the lateral groove becomes the maximum value, from the tire equator to the position 10-2 of the tread width.
2. The method according to claim 1, wherein the distance is set within a range of 2%.
The pneumatic tire for heavy loads according to the description. 3. The lateral groove on the tread surface where the main portion has disappeared, wherein the lateral groove wide remaining portion has a large volume portion having a groove sectional area larger than a groove sectional area at the inner end of the lateral groove main residual portion. 2. The heavy-duty pneumatic tire according to claim 1, wherein a circumferential length of the large volume portion is 5 to 10% of the tread width.