JPH03197206A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To restrain the partial wear of a tread part by positioning a stepped land part cellularized with a pair of peripheral sub-grooves within the specific range of the tread part, and setting a radial difference between the center part of the tread part and the end thereof within the specific range. CONSTITUTION:A land part 20 is formed on the tread part 12 of a tire 10 with a main groove 14 and a pair of sub-grooves 14 respectively extended in a tire peripheral direction. In this case, each sub-groove 16 is so formed as to have a distance K from a tread end to the center position of the land part 20 within a range 0.3 to 0.45 times tread width 2W. In addition, the surface of the land part 20 cellularized with each sub-groove 16 is positioned inward in a tire radial direction, thereby forming a stepped land part 18. Furthermore, a cut line 24 extended in a tire peripheral direction and curved inward in a radial direction is positioned at least on one side of the tread part 12. According to the aforesaid construction, a difference in a tire radial direction between the center and end of the tread part 12 is set to be 0.02 to 0.05 times the tread width 2W.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pneumatic tire that is applied to heavy-duty vehicles such as trucks and buses, and which suppresses the occurrence of uneven wear in the tread portion.

(Prior Art) As shown in Fig. 2, a carcass 1 consists of a plurality of cord layers in which cords are arranged radially in the radial direction of the tire, and cords are arranged in the tire circumferential direction or at a shallow angle to the tire circumferential direction. Radial tires, which are made of cords and belts 2 arranged around the outer circumference of the carcass, have excellent high-speed running performance and handling stability. It is also popular in heavy-duty vehicles such as

The tread pattern of the tires used in these vehicles takes advantage of the characteristics such as low rolling resistance, low skidding, and excellent wear resistance, and uses a plurality of main grooves 3 extending in the circumferential direction of the tire, A so-called rib pattern consisting of land portions 4 divided by main grooves has been preferably used.

(Problem to be Solved by the Invention) However, in tires with a rib pattern, uneven wear called railway wear or river wear occurs along the rib 4's length before the wear life of the tire is reached. In addition to this, uneven wear such as wave-like wear, shoulder drop, and rib punches may occur on the tread of tires used as front wheels or idlers of heavy-duty vehicles. However, if the tires are used continuously as they are, there is a problem in that the tire performance will drop significantly as wear progresses.

The present invention has been made in view of these problems, and one of its objectives is to provide a pneumatic tire for heavy loads that can advantageously suppress uneven wear in the trending portion of the tire.

(Means for Achieving the Object) In order to achieve this object, the present invention provides a heavy-duty pneumatic tire having grooves and land areas partitioned by these grooves on the surface of the tread portion of the tire. A stepped land portion defined by a pair of circumferential minor grooves spaced apart from each other in the width direction of the tire and extending in the circumferential direction thereof, and having a surface located inward in the tire radial direction from the contour line of the tread portion;
A cut is provided in the tread, which is provided within a range of 0.3 to 0.45 times the tread width (2W) from at least one tread end, and extends in the tire circumferential direction and curves inward in the radial direction. The difference in the tire radial direction between the center of the tread and the end of the tread (h
) is a value within the range of 0.02 to 0.05 times the tread width (2W).

(Function) Generally, when a tire rolls in the direction of vehicle travel under load, the ground contact area of the tread portion undergoes shear deformation in the tire tangential direction due to relative movement with the road surface.

However, since the tread of a tire has lower rigidity at its edges than at its center, the distribution of shear force acting on the ground contact area differs in the tire width direction, and the outer area in the tire width direction, that is, the tread The shearing force acting on a portion of the shoulder is larger than that acting on the central portion of the tread, and its direction is oriented in the braking direction.

However, since the surface of the stepped region located in a part of the shoulder is located inward in the tire radial direction from the surface of the tread portion, when the tire is transferred, the surface of the stepped land portion is dragged by the road surface, causing the Since the shear force directed in the braking direction is concentrated in the step area, the shear force in the braking direction that acts on the land area adjacent to the step area is reduced, making it possible to suppress the occurrence of uneven wear in the tread area, and eventually The crown radius R of the tread portion can be made large in order to reduce the drag caused by the difference in diameter between the center portion of the tread and its end portions.

However, during actual driving, in addition to the shear force that acts in the circumferential direction of the tire, side forces that are perpendicular to the equatorial plane of the vehicle also act as the vehicle turns.

However, since a notch is formed on the side surface of the tread portion that extends in the tire circumferential direction and has a bent portion cut inward in the tire radial direction, the rigidity at the tread end is reduced and the ground contact pressure is low. This suppresses the concentration of side force at the tread end, thereby advantageously suppressing the occurrence of uneven wear.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a tread portion 12 of a tire 10 according to the present invention.
It is a diagram showing a cross section of the tire, and since it has a substantially symmetrical structure with respect to the tire equatorial plane S, only half of it is shown. In addition,
Since its internal structure has a radial structure similar to that of the tire shown in FIG. 2, its explanation will be omitted here.

The tread portion 12 has a main groove 14 extending in the tire circumferential direction in a half thereof, and a pair of circumferential grooves 14 formed in at least one shoulder portion apart from the main groove outward in the tire width direction. It includes sub-grooves 16 and land portions 18 defined by the sub-grooves 16 and extending in the circumferential direction of the tire.

Usually, the groove width W of the circumferential main groove 14 is selected within the range of 6% to 8% of the width of the tread portion 12 in the tire width direction, that is, the tread width (2W), although it varies depending on the specifications of each tire. The depth of the groove is determined mainly by considering the drainage performance of the tire.

On the other hand, a pair of circumferential minor grooves 16 that partition the land portion 18
．． 16 shall be provided at a position where the distance K from the tread edge to the center position of the land portion 18 is within a range of 0.3 to 0.45 times the tread width (2W), preferably approximately 0.35 times, The groove depth dS and groove width W5 of these minor grooves are the groove depth d5 and groove width W of the circumferential main groove 14.

are selected to satisfy values within the ranges of 90% to 135% and 7% to 38%, respectively. The surface of the land portion 18 defined by the pair of circumferential minor grooves 16.16 is positioned inward in the tire radial direction from the contour line of the tread portion 12 to form a stepped land portion.

This stepped land portion 18 has a width of 2% to 8%, preferably 4% to 6%, of the trend width (2W), and also extends from the bottom of the circumferential minor groove 16 to the surface thereof. , that is, the height d of the stepped land portion 18. , the groove depth d of the circumferential minor groove 16
, preferably 75% to 80%.

Here, the center portion of the step land portion 18 defined by the circumferential minor grooves 16.16 is measured from the tread end to the width (2W) of 0.
The reason why the stepped land portion 18 is formed in the range of 3 to 0.45 times is that if the stepped land portion 18 is arranged in an area smaller than 0.3 times the tread width (2W), the rigidity of the land portion at the tread end is small. This is because the area located closer to the center of the tread than that area is dragged by the road surface, and uneven wear is likely to occur in the central area. This is because if a region larger than 45 times is formed, the region will be dragged against the road surface when the tire is transferred, and uneven wear of the land portion located at the end of the tread cannot be sufficiently suppressed.

Further, the groove depth d of the circumferential direction minor groove 16 is set to a value within the range of 90% to 135% of the groove depth d of the circumferential direction main groove.
If it is less than 0%, it will not be possible to sufficiently suppress uneven wear after the middle stage of wear, and if it is more than 135%, cracks will occur from the groove bottom.

Then, the groove width Ws is set to 7 of the groove width W1 of the circumferential main groove 14.
% to 38%. If the value is smaller than 7% of the groove width W of the main groove, the groove width of the minor groove will become too small, and when the tire is transferred, it will face the side wall of the minor groove. Since the side walls of the stepped land portions contact each other and the sub groove and the stepped land portion 18 behave as one, the stiffness of the part of the tire including the stepped land portion is increased, and the side walls of the stepped land portion are closer to the center of the tire than those areas. This is because uneven wear tends to occur in the area located in the area where the groove width WS of the minor groove is 38% of the groove width W1 of the circumferential main groove
This is because if it exceeds this, the wear resistance performance will deteriorate.

On the other hand, when the width of the stepped land portion 18 is selected from within the above range, if the width of the stepped land portion is smaller than 2% of the tread width (2W), the rigidity of the stepped land portion 18 in the tire circumferential direction is small. As a result, the ground contact pressure with the road surface decreases more than necessary, and the shear force acting in the braking direction cannot be concentrated in the step area, and the adjacent land portion 20 divided by the circumferential sub-groove 16 The shear force in the braking direction that acts on the land portion 20 increases, making it impossible to effectively prevent uneven wear on the land portion 20. Furthermore, if the width of the step region exceeds 8% of the tread width (2W), , since the rigidity of the stepped land portion 18 in the tire circumferential direction becomes too high and the ground pressure against the road surface increases, the tread portion 1 including the stepped land portion
This is because the wear resistance of No. 2 decreases.

On the other hand, the height d of the stepped land portion 18. is selected from within the above range based on its height d. is larger than 90% of the groove depth dS of the circumferential sub-groove 16, the step land portion 18 will come into contact with the road surface even when a relatively small load is applied to the normal load, and the step land portion 18 will come into contact with the road surface. The shear force in the braking direction cannot be substantially concentrated on the land portion 18, and the height d of the stepped land portion. If it is made smaller than 50% of the groove depth d5 of the sub-groove 16, the stepped land portion 18 will contact the ground less frequently during the wear process, and concentration of shear force in the braking direction cannot be expected. It is.

In this way, the tire 10 having the stepped land portion 18 defined by the pair of circumferential minor grooves 16 located in a portion of at least one shoulder is able to resist shear in the braking direction that acts on the tread portion when traveling on a straight road. force to the step area 18
As a result, uneven wear of the shoulder portion caused by the difference in the tire radial direction of the crown-shaped tread portion, that is, the diameter difference, that is, the land portion 20 facing the step region 18, in particular, Uneven wear at the edges can be effectively prevented. In other words, the diameter difference caused by the crown shape of the tread portion 12 due to tire rotation can be set small, and uneven wear caused by the dragging of a part of the shoulder can be further reduced. The difference (h) in the tire radial direction between the tread edge and the tread edge is 0.02 to 0.05 times the trend width (2W), preferably 0.03 to 0. It was found that it is effective to double the previous value.

By the way, during actual driving, in addition to the shear force that acts in the braking direction of the tires, side force acts in a direction perpendicular to the equatorial plane as the vehicle turns, so a stepped land portion is formed in a part of the shoulder. For tires with a small diameter difference, that is, a tire with a large crown radius R of the tread, the side force tends to concentrate at the tread edge, and the ground pressure at the tread edge increases locally, causing the trend The end portion will be dragged against the road surface.

As a result, a nucleus of uneven wear is generated at the tread end, which progresses to edge wear and wavy wear.

Therefore, as shown in Fig. 1, in the invented tire opening, the rigidity at the tread end is lowered to reduce the ground contact pressure there, preventing a local increase in ground pressure, and In order to reduce drag of the tread end due to forces, at least one side surface 22 of the tread portion is provided with a notch 24 extending in the circumferential direction of the tire and curving inward in the radial direction. However, lowering the rigidity of the tread edge unnecessarily causes a local increase in ground pressure in the tread portion located from the tread edge to the center of the tread, and also increases the wear resistance of the tread edge. This results in a decrease in performance.

Therefore, the tire IO has an opening width of 5% to 75%, preferably 30% to 45%, of the groove width Wm of the circumferential main groove 14, and the tire is radially inward within a range (C) of 0% to 150% of the groove depth (dl) of the circumferential main groove 14, preferably about 70%
A notch 24 is provided in which the opening end is located, and the distance (B) from the notch 24 to the innermost side wall in the tread width direction is within the range of 0.5% to 10% of the tread width (2W). In addition, the groove bottom extends from 20% to 20% of the groove depth (d, ) of the circumferential main groove 14 inward in the tire radial direction from the tread edge.
180% range (A), and at least one bent portion 24b is formed in the middle thereof.

Here, the opening width of the notch 24 is defined as the groove width W of the circumferential main groove 14.
The reason for setting the value within the range of 5% to 75% is that if it is smaller than 5%, the inner walls of the notches 24 will come into contact with each other and become integrated when the tire is transferred, so the rigidity at the tread end will increase. This is because a local increase in ground pressure due to side force occurs, making it easy for uneven wear to occur.On the other hand, if the opening width exceeds 75% of the groove width of the main groove 14, the opening width will increase. This is because, since the large cut 24 is provided, the rigidity at the trend end becomes too low, and the tread end is dragged on the road surface in response to side force, which tends to cause uneven wear.

In addition, the opening end of the notch 24 is moved inward from the tread end in the tire radial direction by 0% to 150% of the groove depth of the circumferential main groove 14.
If it is provided within the range (C) of 1. if it is provided in a range smaller than 0% of the groove depth of the circumferential groove 14. This is because the distance between the notch 24 and the tread edge becomes smaller and the rigidity of the tread end decreases, resulting in the edge remaining in the tread wear process or tearing failure occurring in the notch. On the other hand, if the distance C exceeds 150% of the groove depth of the main groove 14, the rigidity of the tread end becomes high, and the side force acting on the end cannot be alleviated, causing uneven wear. This is because there is no suppressing effect.

Then, set the distance B of the notch 24 to the innermost side wall in the tread width direction from 0.5% to 1% of the tread width (2W).
The reason for locating it within the range of 0% is that if the distance B becomes smaller than 0.5%, the rigidity of the tread end cannot be reduced, and therefore, the local increase in ground pressure due to side force is suppressed. This is because, on the other hand, if the distance B exceeds 10%, the rigidity of the tread end becomes too small, and shoulder drop wear is likely to occur.

Furthermore, the groove bottom of the notch 24 is moved inward in the tire radial direction from the trend end by 20% to 20% of the groove depth (d, ) of the circumferential main groove 14.
The reason for positioning it within the range of 180% is that if the distance A is smaller than 20% of the groove depth of the circumferential main groove 14, the cut 24 in the cross-sectional shape of the tire will have a linear shape, and cracks will occur at the groove bottom of the cut 24. This is because if it exceeds 180%, part of the cut 24 will remain on the tire surface when puffing is performed to remove tread rubber during tire retreading, causing problems in the retreading work.

The reason for providing a bent part in the middle of the cut 24 is that when the cut is a straight line, when the tire is rotated, a load is repeatedly applied to the bottom of the groove of the cut 24 in response to the movement of the tread end, and as a result, the groove is bent. This is because bottom cracks are likely to occur.
This is because by providing the bent portion in the intermediate portion, stress concentration at the groove bottom can be reduced and groove bottom cracks can be effectively suppressed.

Incidentally, in order to investigate the occurrence of uneven wear in the tread portion of the tire of the present invention, a comparison test was conducted with the conventional tire shown in FIG. 2, and the results are shown in the following table. The tires used in the comparative test had two main grooves in the circumferential direction, and the size was 100.
It has a radial structure of OR20.

◎Test tire/invented tire: A tire with the structure shown in Figure 1, with a tread width (
2W) is 200 mm, and the groove width (Wl) of the circumferential main groove is 1.
4 mm, the groove depth (d,) is 14 mm, and the distance (K) from the tread edge to the center of the stepped land part is 65 mm (
) 33% of red width), groove width of each minor groove (WS)
3 mm (21% of the groove width of the circumferential main groove), and its groove depth (
d,) to 14 mm (100% of the groove depth of the circumferential main groove),
The width of the step land (D) is 10 mm (5% of the red width),
Its height (d,) is 11 mm (7 mm of the groove depth of the circumferential minor groove).
9%), the distance in the tire radial direction from the tread edge to the center of the opening of the notch 6 mm ()3% of the tread width), the distance inward in the tire radial direction from the tread edge to the groove bottom of the notch 24 (A ) to 18 mm (1 of the groove depth of the circumferential main groove)
29%), and the distance (B) from the notch 24 to the innermost side wall in the tread width direction is 7 mm (3.5 mm of the tread width).
%), the distance (C) inward in the tire radial direction from the tread edge to the opening end of the notch 24 is 4 mm (29% of the groove depth of the circumferential main groove), and the opening width is 4 mm (circumferential main groove depth). A tire with a groove width of 29%).

- Conventional tire: A tire with the structure shown in Figure 2, with a tread width (2W) of 200 mm and a circumferential main groove width of 13 mm.
mm, and the tire has a groove depth of 14 mm.

◎Test method The difference in the tire radial direction between the center of the tread and the end of the tread, that is, the diameter difference (h), is determined by measuring 0.04 times the tread width (8 mm).
) and 0.09 times (18mm) test tires were assembled on regular rims and regular internal pressure was applied, and they were installed alternately on the front wheels of a 2D-4 car. Amount of change in diameter difference at the end (T, ) and width of uneven wear that occurred along the edge of the land portion along the minor groove (E,)
were measured to evaluate uneven wear resistance.

◎Test results The test results are shown in the table below.

・Amount of change in diameter difference (T,) ・Uneven wear width (Ew) As is clear from this table, in the tire of the present invention, uneven wear in the tread portion can be reduced without substantially increasing the diameter difference in the tread portion. It can be seen that the occurrence of can be suppressed.

(Effects of the Invention) According to the present invention, it is possible to provide a pneumatic tire for heavy loads in which uneven wear does not substantially occur in the tread portion of the tire.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a half part of a pneumatic tire for heavy loads according to the present invention with respect to its equatorial plane, and FIG. 2 is a sectional view of a half part of a conventional pneumatic tire for heavy loads with respect to its equatorial plane. It is a diagram. 1 Carcass 3.14 Main groove 10 Tire 16 Circumferential minor groove 24 Notch 24b Bent part 2 Belt 4.20 Land part 12 Tread part 18 Step land part 24a Opening part Fig. 1 0 /4ffi direction main wing

Claims (1)

[Scope of Claims] 1. A heavy-duty pneumatic tire having grooves and land areas defined by these grooves on the surface of the tread portion of the tire, which extend in the circumferential direction of the tire while being spaced apart from each other in the width direction of the tire. A step land section is defined by a pair of circumferential minor grooves and has a surface located radially inward from the contour line of the tread section.
) is provided within a range of 0.3 to 0.45 times, and extends in the circumferential direction of the tire and is curved inward in the radial direction.
A pneumatic tire for heavy loads, characterized in that the difference (h) in the tire radial direction between the center of the tread and the end of the tread is set to a value within the range of 0.02 to 0.05 times the tread width (2W). .