JP2001121923A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that controls a change in operation stability due to abrasion of tread. SOLUTION: A groove wall 28A on a shoulder side of a circumferential direction main groove 28 is formed in protruding arc shape and a groove wall 28B on a tire equatorial plane CL side is formed in recessed arc shape. Operation stability at the time of cornering is affected by characteristic of grounding region outside turning radius direction of the tire equatorial plane CL. When a tire is new, a direction of crushing force (summation: F1+F2) of the ground region outside turning radius direction of the tire equatorial plane CL is the same direction as cornering force CF to be a direction to enhance the cornering force CF. After the middle period of abrasion, the direction of crushing force (summation: F1+F2) is opposite to that of the cornering force CF for controlling an increasing change in the cornering force due to abrasion to control a change in operation stability originated from an increase of the cornering force CF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire provided with a plurality of circumferential main grooves extending in the tire circumferential direction in a tread, and more particularly to a pneumatic tire in which a change in steering stability due to tread wear is suppressed. About.

[0002]

2. Description of the Related Art In a general pneumatic tire, a plurality of circumferential main grooves extending along the tire circumferential direction are formed in a tread in order to ensure wet performance.

[0003]

In recent years, as the performance of vehicles has increased, it has been required to further improve the steering stability during high-speed running. However, as the tread wears, the steering stability changes. There is a problem, and a countermeasure is desired.

[0004] The present invention, in view of the above facts, relates to a pneumatic tire that suppresses a change in steering stability due to tread wear.

[0005]

As a result of various experiments, the inventor has found that the cornering force changes due to tread wear, which adversely affects the steering stability.

The invention described in claim 1 has been made in view of the above fact, and is a pneumatic tire provided with a plurality of circumferential main grooves extending in a tire circumferential direction on a tread, When comparing a first portion adjacent to the shoulder side of the circumferential main groove and a second portion adjacent to the tire equatorial plane side of the circumferential main groove in the land portion defined by the main direction groove. The crushing force generated on the land portion when the land portion comes into contact with the ground is larger in the second portion than in the first portion when the land portion is new. The crushing force generated in the first portion gradually decreases, and the crushing force generated in the first portion gradually increases.

Next, the operation of the pneumatic tire according to the first aspect will be described.

When the land portion of the tread formed of rubber (elastic body) comes into contact with the ground, a force acts on the land portion in the vicinity of the edge of the circumferential main groove so as to bulge toward the circumferential main groove side in parallel with the road surface. ,
A crushing force acts on the tread as a reaction to this force.

In the pneumatic tire according to the first aspect, an increase in cornering force due to abrasion of the tread is suppressed by utilizing the crushing force.

[0010] When the vehicle corners, the contact area increases outside the tire equatorial plane in the turning radius direction and decreases inside the tire equatorial plane in the turning radius direction. The load on the tread portion of the vehicle increases. That is, at the time of cornering, the tread portion on the outer side in the turning radial direction of the tire equatorial plane greatly affects the characteristics (steering stability and the like) of the tire.

In the pneumatic tire according to the first aspect, the land portion on the tire radial direction outside of the tire equatorial plane is:
When new, the crushing force of the second portion adjacent to the tire equatorial plane side (the direction is the tire equatorial plane) is smaller than the crushing force of the first portion adjacent to the shoulder side of the circumferential main groove (the direction is the shoulder direction). Direction) is large, but as the tread wears, the crushing force generated in the second portion gradually decreases and the crushing force generated in the first portion gradually increases. The direction of the outer crushing force (sum) is the same direction as the cornering force, and the direction of the cornering force is defined as the direction in which the cornering force is strengthened. In the opposite direction, the cornering force can be reduced, which reduces the cornering force due to tread wear. Suppressing large, it is possible to suppress the steering stability of changes due to an increase in cornering force.

[0012] The invention according to claim 2 is a pneumatic tire provided with a plurality of circumferential main grooves extending in the tire circumferential direction on a tread, wherein the tire is viewed in a cross section along the tire rotation axis. The angle of the opening side portion with respect to the normal line set on the tread surface of the shoulder side groove wall of the circumferential main groove is θ1, the angle of the groove bottom side portion with respect to the normal line set on the tread surface of the shoulder side groove wall is θ2, The angle of the opening side portion with respect to the normal to the tread of the groove wall on the tire equatorial plane side of the circumferential main groove is θ3, and the angle of the groove bottom side to the normal to the tread of the groove wall on the tire equatorial plane side is the same. When the angle is θ4, θ1> θ2, θ3 <
It is characterized by satisfying θ1, θ2 <θ4, θ3 <θ4.

Next, the operation of the pneumatic tire according to claim 2 will be described.

The crushing force is affected by the angle of the groove wall of the circumferential main groove, and when the groove wall is lying (when the angle of the groove wall of the circumferential main groove with respect to the normal to the tread is large). In the case where the crushing force is small and the groove wall is raised (when the angle of the groove wall of the circumferential main groove to the normal to the tread is small)
The crushing force is large (because the crushing force increases as the amount of the swelling in the lateral direction increases).

In the pneumatic tire according to the second aspect, the angle of the opening side portion with respect to the normal to the tread surface of the groove wall on the shoulder side of the circumferential main groove is θ1, and the angle of the opening side portion is set on the tread surface of the groove wall on the shoulder side. The angle of the groove bottom side portion with respect to the normal line is θ2, the angle of the opening side portion with respect to the normal line on the tread surface of the groove wall on the tire equatorial plane side of the circumferential main groove is θ3, and the angle of the groove wall on the tire equatorial plane side is The angle of the groove bottom side with respect to the normal set on the tread is θ4
Where θ1> θ2, θ3 <θ1, θ2 <θ4,
Since θ3 <θ4 is satisfied, the crushing force of the first portion adjacent to the shoulder side of the circumferential main groove (at the time of a new product) in the land portion on the outer side in the turning radial direction of the tire equatorial plane of the pneumatic tire is new. The crushing force of the second portion adjacent to the tire equatorial plane side is larger than that of the shoulder direction (the direction is the tire equatorial plane direction), but the crushing generated in the second portion as the tread wears. Since the force gradually decreases and the crushing force generated in the first portion gradually increases, the crushing force (sum total) on the outer side of the tire equatorial plane in the turning radial direction is increased in the same direction as the cornering force when the product is new, and the cornering force is increased. After the middle stage of wear, the direction of the crushing force (total) outside the turning radius of the tire equatorial plane is set to the direction opposite to the cornering force. Can in the direction of decreasing the nulling force, thereby suppressing an increase in cornering force due to the wear of the tread, it is possible to suppress the steering stability of the change due to an increase in cornering force.

According to a third aspect of the present invention, in the pneumatic tire according to the second aspect, an angle of the shoulder-side groove wall with respect to a normal line erected on the tread surface is smooth from the opening side to the groove bottom side. And the angle of the groove wall on the tire equatorial plane side with respect to the normal set on the tread surface gradually increases from the opening side to the groove bottom side.

Next, the operation of the pneumatic tire according to claim 3 will be described.

In the pneumatic tire according to the third aspect, the angle of the shoulder-side groove wall with respect to the normal line formed on the tread surface smoothly gradually decreases from the opening side to the groove bottom side. Because the angle with respect to the normal line on the tread of the groove wall gradually increases from the opening side to the groove bottom side,
The change in crushing force accompanying tread wear becomes smooth.

According to a fourth aspect of the present invention, in the pneumatic tire according to the second aspect, the shoulder-side groove wall has a convex arc shape at a connection portion with the tread surface, and the tire equatorial plane-side groove wall has a groove. It is characterized in that the connecting portion with the bottom has a concave arc shape.

Next, the operation of the pneumatic tire according to claim 4 will be described.

In the pneumatic tire according to the fourth aspect, the shoulder-side groove wall has a convex arc shape at a connection portion with the tread surface, and the tire equatorial surface side groove wall has a concave arc shape at a connection portion with the groove bottom. Therefore, the angle of the groove wall with respect to the normal line on the tread surface changes smoothly, and the change in steering stability can be suppressed smoothly.

Preferably, the convex arc-shaped portion of the shoulder-side groove wall is smoothly connected to the tread surface, and the concave arc-shaped portion of the tire equatorial plane-side groove wall is smoothly connected to the groove bottom. .

According to a fifth aspect of the present invention, in the pneumatic tire according to the fourth aspect, the radius of curvature of the arc-shaped portion of the groove wall is R, and the depth of the circumferential main groove is H. In addition, 0.5H ≦ R ≦ H is satisfied.

Next, the operation of the pneumatic tire according to claim 5 will be described.

In the case where the groove wall has an arc shape, if the curvature radius R is less than 0.5H, as shown in FIG. 5, the radius of curvature of the convex arc portion of the shoulder side groove wall is too small to increase the cornering force. The effect disappears immediately,
The effect of suppressing the cornering force does not appear unless the radius of curvature of the concave arc portion of the groove wall on the tire equatorial plane side is too small and wears considerably, and there is no smoothness in the effect of suppressing the increase of the cornering force, or the cornering force In some cases, it is not possible to suppress an increase in the vehicle stability, and it is not possible to suppress a change in steering stability.

When the radius of curvature R of the arc shape of the groove wall exceeds the groove depth H, the groove width of the circumferential main groove is increased as shown in FIG. 6 and the ground contact area is reduced, or as shown in FIG. The angle with respect to the normal line on the tread of the shoulder-side groove wall when it is new is too small, the effect of increasing the cornering force when it is new is reduced, and the tread on the tire equatorial surface side at the groove bottom side In some cases, the angle with respect to the line cannot be increased, and the effect of suppressing the cornering force in the latter stage of wear decreases, and the increase in the cornering force cannot be suppressed as a whole, making it impossible to suppress changes in steering stability. is there.

[0027]

Next, an embodiment of the pneumatic tire of the present invention will be described with reference to FIGS.

As shown in FIGS. 1 and 2, the pneumatic tire 10 of the present invention includes a carcass 14 that straddles from one bead portion 12 to the other bead portion 12 in a toroidal manner.

In the present embodiment, the carcass 14 is composed of one carcass ply 16, and the carcass ply 16 has the bead core 18 folded back from the inner side to the outer side in the tire radial direction. May be.

A belt 20 is disposed outside the carcass 14 in the tire radial direction.

A tread 26 made of thick rubber is disposed outside the belt 20 in the tire radial direction.

A plurality of (four in the present embodiment) circumferential main grooves 28 having a depth H are formed on the tread 26 so as to extend in the tire circumferential direction and to be spaced apart in the tire width direction. A portion 29 (the land portion may be a rib continuous along the tire circumferential direction, or may be a block provided with a lateral groove).

In the circumferential main groove 28, the shoulder-side groove wall 28A has an arc shape with a radius of curvature r1 in which the connection side with the tread surface 30 is convex outward of the tire, and the groove wall 28B on the tire equatorial plane CL side is a groove. It has an arc shape with a radius of curvature r2 in which the connection side with the bottom 28C is concave.

The arc-shaped portion having a radius of curvature r1 of the groove wall 28A and the tread surface 30 are smoothly connected.
The arc-shaped portion of B having a radius of curvature r2 is smoothly connected to the groove bottom portion 28C.

Here, in the present embodiment, r1 = r2 = H
(Groove depth) = 8 mm, and the opening side of the groove wall 28A is the tread surface 3
0 smoothly (θ1 in the present invention: 90
°), on the groove bottom side, it is substantially perpendicular to the groove bottom 28C (θ2: 0 ° in the present invention).

The opening side of the groove wall 28B is substantially perpendicular to the tread surface 30 (θ3 = 0 ° in the present invention), and the groove wall 28B is smoothly connected to the groove bottom 28C on the groove bottom side (θ4 in the present invention). : 90 °). (Operation) Next, the operation of the pneumatic tire 10 of the present embodiment will be described.

Tread 26 made of rubber (elastic body)
When the land portion 29 of the tread 26 comes into contact with the road surface, a force to bulge in the vicinity of the edge of the circumferential main groove 28 toward the circumferential main groove 28 side in parallel with the road surface acts on the land portion 29 of the tread 26. Crushing forces F1 and F2 act as reaction forces of the force.

When the vehicle corners, the ground contact area increases outside the tire equatorial plane CL in the turning radius direction and decreases inside the tire equatorial plane CL in the turning radial direction.

As shown in FIG. 1A, in the land portion 29 on the outer side in the turning radial direction of the tire equatorial plane CL of the pneumatic tire 10 (in the direction of the arrow OUT in FIG. Near the opening end on the tire equatorial plane CL side (in the direction of the arrow IN in the figure) than the crushing force F1 near the opening end on the shoulder side (the direction of the arrow OUT in the figure) (the first part of the present invention) (the present invention). The crushing force F2 of the second portion) becomes large (because the angle of the groove wall 28A> the angle of the groove wall 28B in the ground contact portion), and when the tire is new, the tread 26 is located outside the tire equatorial plane CL in the turning radial direction. Since the crushing force (total: F1 + F2) is in the same direction as the cornering force CF, the direction is to increase the cornering force CF (here, the greater the length of the arrow F, the greater the force). .

On the other hand, after the middle stage of wear, as shown in FIG. 1B, the crushing force F1 near the shoulder-side opening end of the circumferential main groove 28 is smaller than the crushing force F1 near the opening end on the tire equatorial plane CL side. The lashing force F2 becomes small (because the angle of the groove wall 28A <the angle of the groove wall 28B at the ground contact portion), and the crushing force (total: F1 + F2) of the tread 26 on the tire equatorial plane CL in the turning radial direction is reduced. Since the direction is opposite to that of the cornering force CF, the direction is a direction in which the cornering force CF is suppressed.

Therefore, the increase in the cornering force CF due to the wear of the tread 26 is suppressed, and the change in the steering stability due to the increase in the cornering force CF is suppressed.

In this embodiment, r1 = r2 = H =
8 mm, but when H = 8 mm, r1 and r
2 may be between 4 and 8 mm.

As shown in FIG. 3, r1 <H and r2 <H
In this case, it is preferable that the arc-shaped portion having the curvature radius r1 of the groove wall 28A and the tread surface 30 be smoothly connected, and the arc-shaped portion having the curvature radius r2 of the groove wall 28B be smoothly connected to the groove bottom portion 28C.

The increase or decrease of the cornering force CF due to the creshing force is large in a low load region where the spread of the contact with the ground and the progress thereof have not yet tended to plateau, and the cornering force C is large.
An increase in F manifests its effect on the rear wheels and increases the stability of the vehicle. (Other Embodiments) In the above embodiment, the shoulder-side groove wall 28A has an arc shape with a radius of curvature r1 in which the connection side with the tread surface 30 is convex to the outside of the tire.
The groove wall 28B on the L side has an arc shape with a radius of curvature r2 in which the connection side with the groove bottom 28C is concave. However, the present invention is not limited to this, and the angle with respect to the normal HL set on the tread surface 30 is changed to the groove bottom side. If the angle with respect to the normal HL tends to increase toward the groove bottom side, the cross-sectional shapes of the groove walls 28A and 28B are shapes other than the arc shape having a single radius of curvature. There may be.

For example, the cross-sectional shape of the groove walls 28A and 28B may be a curved shape having a plurality of radii of curvature, a bent shape having a plurality of bent portions (a plurality of straight portions are connected at an angle). Shape). (Test Example) In order to confirm the effect of the present invention, a tire of a conventional example and a tire of the embodiment to which the present invention was applied were prepared, and the cornering power of each tire was 40% lower than that of a new tire by a test machine in a room. It was measured at the time of wear. -Example tire: The tire described in the above embodiment, the groove depth of the circumferential main groove is 8 mm, the radius of curvature r1 of the shoulder-side groove wall is 8 mm, and the radius of curvature of the groove wall on the tire equatorial plane side is This is a tire with r2 of 8 mm. Conventional tire: As shown in FIG. 3, the groove depth H is 8 mm.
A tire having a circumferential groove 32 whose cross-sectional shape is bilaterally symmetrical (substantially U-shaped) with respect to a normal HL standing on the tread surface.

Each of the tires had a tire size of 195.
/ 65R14.

The results of the test are as described in Table 1 below. The results are indexed with the cornering power of the conventional tire at the beginning of wear (when the tire is new) as 100. The larger the numerical value, the greater the cornering power and the better the maneuverability.

[0048]

[Table 1]

As a result of the test, it is understood that the tire of the example to which the present invention is applied has a smaller change in the cornering power as compared with the conventional tire. Accordingly, it is clear that the tire of the example has a smaller change in steering stability due to tread wear than the conventional tire.

[0050]

As described above, the pneumatic tires according to claims 1 to 5 have the above-described structure.
It has an excellent effect that a change in steering stability due to tread wear can be suppressed.

Since the pneumatic tires according to the third to fifth aspects have the above-described structure, the pneumatic tire has an excellent effect that a change in steering stability can be suppressed smoothly.

[Brief description of the drawings]

FIG. 1A is a sectional view of a tread when a pneumatic tire according to an embodiment of the present invention is new, and FIG. 1B is a sectional view of the tread when worn.

FIG. 2 is a cross-sectional view along a tire axis of the pneumatic tire according to one embodiment of the present invention.

FIG. 3 is a sectional view of a tread of a pneumatic tire according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view along a tire axis of a pneumatic tire according to a conventional example.

FIG. 5 is a cross-sectional view of the circumferential main groove when the radius of curvature of the arc-shaped portion of the groove wall is too small.

FIG. 6 is a cross-sectional view of the circumferential main groove when the radius of curvature of the arc-shaped portion of the groove wall is too large (Example 1).

FIG. 7 is a cross-sectional view of the circumferential main groove when the radius of curvature of the arc-shaped portion of the groove wall is too large (Example 2).

[Explanation of symbols]

 Reference Signs List 10 Pneumatic tire 20 Belt 26 Tread 28 Circumferential main groove 28A Groove wall 28B Groove wall F1 crushing force F2 crushing force

Claims (5)

[Claims] 1. A pneumatic tire having a plurality of circumferential main grooves extending in a tire circumferential direction on a tread, wherein a shoulder of the circumferential main groove is provided on a land portion defined by the circumferential main groove. Force generated in the land portion when the land portion comes into contact with the ground when the first portion adjacent to the ground portion and the second portion adjacent to the tire equatorial plane side of the circumferential main groove are compared. When the new part, the second part is larger than the first part, and the crushing force generated in the second part gradually decreases as the tread wears, The pneumatic tire according to claim 1, wherein the generated crushing force is gradually increased. 2. A pneumatic tire having a plurality of circumferential main grooves extending in a tire circumferential direction in a tread, wherein a shoulder of the circumferential main groove when viewed in a cross section along a tire rotation axis. The angle of the opening side portion with respect to the normal line formed on the tread surface of the side groove wall is θ1, the angle of the groove bottom side portion with respect to the normal line formed on the tread surface of the shoulder side groove wall is θ2, the tire of the circumferential main groove is When the angle of the opening side with respect to the normal set on the tread of the equatorial plane groove wall is θ3, and the angle of the groove bottom side with respect to the normal set on the tread of the equatorial plane groove wall is θ4. , Θ1> θ2, θ3 <θ1, θ2 <θ4, θ
A pneumatic tire characterized by satisfying 3 <θ4. 3. An angle of the shoulder-side groove wall with respect to a normal line formed on the tread surface gradually decreases gradually from the opening side to the groove bottom side, and a normal line formed on the tread surface of the groove wall on the tire equatorial plane side. 3. The pneumatic tire according to claim 2, wherein the angle with respect to the opening gradually increases from the opening side to the groove bottom side. 4. The groove wall on the shoulder side has a convex arc shape at the connecting portion with the tread surface, and the groove wall on the tire equatorial plane has a concave arc shape at the connecting portion with the groove bottom. 3. The pneumatic tire according to 2. 5. When the radius of curvature of the arc-shaped portion of the groove wall is R, and the groove depth of the circumferential main groove is H, 0.5
The pneumatic tire according to claim 4, wherein H ≦ R ≦ H is satisfied.