JP3021694B2 - Pneumatic radial tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire mounted on a vehicle such as an automobile.

[0002]

2. Description of the Related Art Conventionally, a tread 62 of a pneumatic radial tire 60 mounted on a vehicle such as an automobile shown in FIG.
The plurality of tread land portions 6 are formed by a main groove 64 along the circumferential direction of the tire surface and a lug groove 66 along the tire width direction.
It is divided into eight. As shown in the contact pressure distribution diagram P of the tread land portion 68 in FIG. 8 , the pneumatic radial tire 60
When the lateral force of the tire, that is, the so-called side force does not act on the tread land portions 68, the contact pressure of the tread land portions 68 is substantially equally distributed in each tread land portion 68.

[0003] As shown in FIG . 6 , the vehicle corners and the tread land portion 66 of the pneumatic radial tire 60 is turned on.
When the side force (arrow SF in FIG. 6 ) acts on the ground contact surface, as shown in the contact pressure distribution diagram P1 in FIG. 6 , the end of the tread land portion 66 on the side where the side force enters (the left side in FIG. 6 ) . The contact pressure of 66A increases, and the contact pressure of the end 66B on the side where the side force comes off (the right side in FIG. 6 ) decreases. Incidentally, the tread land portion 66 of the pneumatic radial tire 60 has high rigidity as a whole.
Although the overall deformation of the tread land 6 itself is small, when the contact pressure of the end 66A of the tread land portion 66 on the side where the side force enters (the left side in FIG. 6 ) increases, the end 66A of the tread land portion 66 becomes the tread land portion 66 as shown in FIG. It is caught between the contact surface and the road surface 72, and a part of the contact surface of the tread land portion 66 is separated from the road surface 72, and the contact area of the tread land portion 66 decreases.

That is, as shown in FIG. 9, the relationship between the slip angle SA and the side force SF is such that the side force SF increases as the slip angle SA increases, but when the side force SF increases, the land land SF increases. Since the end 66A of the portion 66 on the side where the side force SF enters is involved, the end 66A on the side where the side force SF enters does not bear the side force SF.

For this reason, the upper limit value S of the side force SF is
F1 is lower than the value SF0 determined by the friction coefficient μ of the tread rubber, and the grip performance at the time of cornering is lowered, and the tread land portion 66 is liable to cause uneven wear.

[0006]

SUMMARY OF THE INVENTION In consideration of the above fact, the present invention can prevent uneven distribution of the contact pressure of each tread land portion at the time of side force action, improve grip performance at cornering, and improve uneven wear. It is an object of the present invention to obtain a pneumatic radial tire capable of suppressing the occurrence of a tire.

[0007]

The present invention is defined by a main groove formed on a tread along a tire circumferential direction and a lug groove intersecting the main groove and formed along a tire width direction. A pneumatic radial tire having a tread land portion, wherein a depth of the tread land portion is smaller than a depth of the main groove and a depth of the lug groove, and is smaller than a width of the main groove and a width of the lug groove. width is characterized and the peripheral portion divided by a narrow minor groove, that is provided and a central portion that protrudes in a substantially spherical shape to the tire radially outwardly than the surrounded on an outer peripheral portion and the outer peripheral portion.

[0008]

According to the present invention having the above structure, the land portion is divided by the sub-groove having a depth smaller than the depth of the main groove and the lug groove and having a width smaller than the width of the main groove and the lug groove. An outer peripheral portion, and a central portion surrounded by the outer peripheral portion and protruding substantially spherically outward in the tire radial direction from the outer peripheral portion. For this reason, the contact pressure when the tread land portion contacts the road surface is higher in the central portion than in the outer peripheral portion.

When the side force acts on the contact surface, the contact pressure of the tread land portion near the end where the side force enters, that is, the contact pressure at the outer peripheral portion increases. However, since the contact pressure at the center portion is higher than that at the outer peripheral portion, the contact pressure is originally higher. Even when the contact pressure at the outer peripheral portion increases, the distribution of the contact pressure at the tread land portion is not biased toward the side for entering the side force of the tread land portion.

As described above, the rise of the contact pressure acting on the end on the side where the side force enters is suppressed in the tread land portion when the side force acts, as compared with the tread land portion of the conventional structure. Is prevented, and the contact area of the tread land portion is prevented from being reduced. Therefore, the grip performance at the time of cornering can be improved and uneven wear of the tread land portion can be suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, in the tread 12 of the pneumatic radial tire 10 of this embodiment, four main grooves 14 are formed along the tire circumferential direction on the ground contact surface along the tire width direction. I have. On the tread 12, a lug is inclined from the vicinity of the tire equatorial plane 16 to the shoulder portion 18 of the tread 12 toward the tire rotation direction (the side that first comes into contact with the road surface, the lower side in FIG. 1) when the vehicle advances. Groove 2
0 are formed at predetermined intervals in the tire circumferential direction. Thus, the tread 12 has a plurality of tread land portions 2 divided by four main grooves 14 and a plurality of lug grooves 20.
2 are formed.

The tread land portion 22 is divided into an outer peripheral portion 28 and a central portion 26 surrounded by the outer peripheral portion 28 by a narrow groove 24 as a sub-groove.
6 and the outer peripheral portion 28 can be independently compressed and deformed.

The plane shape of the central portion 26 is the tread land portion 22.
Is formed in a shape substantially similar to the planar shape of
The contact area of No. 6 is 40 to 80% of the contact area of the outer peripheral portion 28. When the contact area of the central portion 26 is less than 40%, the ratio of the outer peripheral portion 28 to bear the contact pressure increases, and it is difficult to suppress the uneven distribution of the contact pressure of the tread land portion 22 at the time of side force action.
If the ground contact area exceeds 80%, when the tread land portion 22 is grounded, the rate at which the central portion 26 is compressed in the vertical direction of the ground contact surface decreases, and the outer peripheral portion 28 may not contact the road surface. In this embodiment, the central portion 2
The contact area of No. 6 is 50% of the contact area of the outer peripheral portion 28.

As shown in FIG. 2, the depth D1 of the main groove 14 is, for example, 8 mm in this embodiment. The central portion 26 has a central portion protruding in a substantially large spherical shape, and the ground contact surface of the central portion 26 is located radially outward with respect to the contact surface of the outer peripheral portion 28. The protruding dimension H of the central portion of the central portion 26 at the center of the contact surface is set to 5% or less, preferably 2 to 3% with respect to the depth D1 of the main groove 14,
If it is less than 2%, the rate of increase in the contact pressure of the central portion 26 is small, and if it is 5% or more, the contact pressure of the central portion 26 is too high and the outer peripheral portion 28 may not contact the road surface. In the present embodiment, the protruding dimension H of the central part of the central part 26 at the ground contact surface is, for example, 0.2 mm.

On the other hand, the depth D2 of the narrow groove 24 is in the range of 30 to 100% with respect to the depth D1 of the main groove 14, and the depth D2 of the narrow groove 24 is smaller than the depth D1 of the main groove 14. On the other hand, if it is less than 30%, when the central portion 26 contacts the road surface, the central portion 26 surrounded by the outer peripheral portion 28 cannot spread in the direction along the contact surface, and the contact pressure of the central portion 26 increases. There is a possibility that the outer peripheral portion 28 does not touch the road surface at the same time. In this embodiment, the depth D2 of the narrow groove 24 is, for example, 3 mm.

The width W of the narrow groove 24 is set so as not to contact the outer peripheral portion 28 when the central portion 26 is grounded and crushed and the outer peripheral portion facing the outer peripheral portion 28 of the central portion 26 is enlarged. It is at least 0.3 mm or more and 1 mm or less, preferably 0.5 mm or more and 1 mm or less, for example, 0.5 mm
It has been. If the groove width W of the narrow groove 24 exceeds 1 mm, the rigidity of the tread land portion 22 may decrease, which is not preferable.

Next, the operation of this embodiment will be described. In the pneumatic radial tire 10 of the present invention, the tread land portion 22 is divided into the central portion 26 and the outer peripheral portion 28 by the narrow groove 24, and the contact surface of the central portion 26 is in the tire radial direction with respect to the contact surface of the outer peripheral portion 28. It protrudes outward. For this reason, when the tread land portion 22 comes into contact with the road surface, the central portion 26 is compressed more than the outer peripheral portion 28, and as shown in the ground pressure distribution diagram P2 in FIG. The contact pressure is higher than the contact pressure near the outer peripheral portion 28.

As shown in FIG. 4, when the vehicle corners and a side force (arrow SF in FIG. 4) acts on the contact surface of the tire, the contact pressure of the tread land portion 22 is increased to the end of the tread land portion 22 on the side where the side force enters. In this case, the contact pressure at the end 28A of the outer peripheral portion 28 on the side where the side force enters is increased. However, the contact pressure of the central portion 26 is reduced to the outer peripheral portion 28.
Therefore, even if the ground pressure near the end of the tread land portion 22 on the side where the side force enters, ie, near the end 28A of the outer peripheral portion 28 on the side where the side force enters, increases, the side force is increased. The contact pressure in the vicinity of the end 28A on the entry side does not exceed the contact pressure of the central portion 26. As a result, as shown in the contact pressure distribution diagram P3 in FIG. The contact pressure is substantially equalized and the end 2 on the side where the side force enters
Only the contact pressure near 8A does not significantly increase as compared to the portion other than the vicinity of end 28A.

Further, since the central portion 26 is surrounded by the outer peripheral portion 28, the side force shown in FIG.
Not only in the direction of F) but also when the side force opposite to the side force shown in FIG. 4 acts, the ground pressure acting on the tread land portion 22 is substantially equalized. Therefore, when mounting the pneumatic radial tire 10 on a vehicle, there is no need to distinguish between the left and right sides of the tire.

As described above, since the uneven distribution of the contact pressure of the tread land portion 22 at the time of the side force action is prevented, as shown by the imaginary line in FIG.
2 approaches the value SF0 determined by the friction coefficient μ of the tread rubber, whereby the grip performance at the time of cornering can be improved and uneven wear can be suppressed.

Furthermore, even when a force along the tire circumferential direction acts on the tread land portion 22 during braking and driving of the vehicle, the side of the tread land portion 22 where the force along the tire circumferential direction enters. The contact pressure acting on the tread land portion 22 is substantially equalized only without significantly increasing the contact pressure in the vicinity of the end.

The tread land portion 22 has a central portion 26 and an outer peripheral portion 28 which are separated from each other and independently compressed and deformed. Each of the 28 contact surfaces is worn by substantially the same size. (Experimental example) Pneumatic radial tire 10 of the embodiment (tire size 2
25 / 50R16) and a conventional pneumatic radial tire 60 (FIG. 5) are mounted on wheels 8J-16, respectively.
At an internal pressure of 2.8 kg / cm ² , a load of 400 kg, and a speed of 50 km / h, the maximum side force SF was measured at a slip angle SA of 0 ° to 15 °. Table 1 shows the maximum side force of a conventional pneumatic radial tire. The index was expressed as an index with SF being 100.

[0024]

[Table 1]

The above results clearly show that the pneumatic radial tire 10 of the embodiment is superior to the pneumatic radial tire 60 of the conventional example.

[0026]

Since the present invention has the above-described structure, uneven distribution of the ground pressure on each tread land portion at the time of side force action can be prevented, grip performance at cornering can be improved, and uneven wear can be suppressed. It has an excellent effect that it can be performed.

[Brief description of the drawings]

FIG. 1 is a plan view showing a tread of a pneumatic radial tire according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a meridional sectional view showing a contact pressure distribution on a tread land where a side force is not acting.

FIG. 4 is a meridional sectional view showing a contact pressure distribution on a tread land portion on which a side force acts.

FIG. 5 is a plan view showing a tread of a conventional pneumatic radial tire.

FIG. 6 is a meridional sectional view showing a contact pressure distribution of a tread land portion when a side force acts on a conventional pneumatic radial tire.

FIG. 7 is a cross-sectional view showing a state in which a tread land portion of a conventional pneumatic radial tire is deformed by a side force.

FIG. 8 is a meridional sectional view showing a contact pressure distribution when a conventional pneumatic radial tire is stopped.

FIG. 9 is a graph showing a relationship between a slip angle and a side force.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Pneumatic radial tire 12 Tread 14 Main groove 20 Lug groove 22 Tread land part 24 Narrow groove (sub groove) 26 Central part 28 Outer part

Claims (1)

(57) [Claims] 1. A pneumatic radial having a tread land portion defined on a tread by a main groove formed along a tire circumferential direction and a lug groove intersecting the main groove and formed along a tire width direction. The tire is divided into the tread land portion by a sub-groove having a depth smaller than the depth of the main groove and the lug groove and a width smaller than the width of the main groove and the width of the lug groove. Outer periphery and front
A pneumatic radial tire is characterized by providing a central portion that protrudes in a substantially spherical shape is surrounded by the serial peripheral portion and the radially outward than the outer peripheral portion.