JP3527673B2 - Pneumatic tire - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pneumatic tire capable of improving wandering performance.

[0002]

2. Description of the Related Art Pneumatic tires, particularly pneumatic tires for light trucks, have higher tread rigidity than tires for passenger cars. Easy to take the handle. Therefore, for small truck tires, there is a strong demand for improvement in such stable performance during rutting, that is, wandering performance.

Conventionally, in order to improve the wandering performance, methods such as reducing the radius of curvature in the meridional section of the tread surface and narrowing the tread width have been used, but these are steering stability. However, there is a problem that the various running performances of the tire are deteriorated.

Therefore, in recent years, as shown in FIG. 5, the camber thrust CT, which is the lateral force generated when a tire is given a camber angle θ and is rolled, is increased to the positive side, and this camber thrust CT is directed in a rut riding direction. It has been proposed to improve wandering performance by acting. The camber thrust CT is usually expressed as plus (+) when it acts on the inclined side and as minus (-) when it acts on the opposite side of the inclination.

Here, the camber thrust CT is presumed to be generated by the following mechanism. That is, as shown in FIG. 4, when the rolling tire is grounded with a camber angle θ, the tread point Pt on the tread surface before grounding is the tread point on the road surface due to tire deformation after grounding. Move to Pt '. Further, the belt point P on the outer surface of the belt layer B corresponding to the tread point Pt
After the ground contact, b moves to the belt point Pb '.

At this time, since the belt layer B is a non-stretchable body composed of a belt cord, the belt point is from Pb to Pb '.
However, since the tread rubber is stretchable, the tread point moves from Pt to Pt 'substantially parallel to the tire equatorial plane. Therefore, a lateral displacement D'is generated between the points Pt 'and Pb', and a lateral force F proportional to the displacement D'is generated.

The lateral force F is such that the tread point Pt 'is at the belt point Pb' in the tread outer area on the inclined side (left side in the figure).
It is displaced more toward the inclined side than the belt, and on the contrary, in the central region of the tread on the opposite side (the right side in the figure), the tread point Pt ′ is displaced toward the opposite side of the belt point Pb ′, and thus becomes negative. Occur. Then, a camber thrust CT is generated as a resultant force of each lateral force F on the entire ground contact surface S.

Therefore, in order to increase the camber thrust CT to the positive side (hereinafter, it may be referred to as improving the camber thrust CT), the ground contact surface shape is improved,
The proportion of the outer surface area portion So in which the lateral force F on the positive side is generated in the contact surface S is increased, or the value of the displacement D ′ itself in the outer area of the tread is increased, or the lateral force generated by this displacement D ′ is increased. It is necessary to increase the value of force F.

Even when the camber angle θ is 0 °, the point P
A lateral force is generated due to the displacement D (shown in FIG. 4) between t and Pb. However, since the displacement, the lateral force, the contact surface shape and the like are substantially symmetrical about the tire equator, the camber thrust itself is It becomes 0 (zero).

Therefore, in the present invention, the ratio Tc of the average thickness Tc in the central region of the tread rubber to the average thickness To in the outer region thereof is Tc.
/ To is basically set to 1 to 0.75, the displacement D'in the outer area can be increased, the camber thrust is improved, and the wandering performance is improved without changing the tread radius or tread width. The purpose of the invention is to provide a pneumatic tire.

[0011]

In order to achieve the above object, the invention of claim 1 of the present application comprises a carcass extending from the tread portion to the side wall portion to the bead core of the bead portion,
A pneumatic tire comprising a belt layer disposed inside the tread portion and outside in the radial direction of the carcass, wherein the tire tread edge side forms a radius of 6 ° with respect to the tire equator line in the tire meridian section. A contact point J with which a line segment inclining inward contacts is in the tread surface, and between the contact point J and the tire equator point of the tread rubber between the tread surface and the radial outer surface of the belt layer. The ratio Tc / To between the average thickness Tc of the central region of the above and the average thickness To of the outside region between the contact point J and the tread edge is smaller than 1 and larger than 0.75. Thus, the tread radius Rt which is the radius of the tread surface in the cross section is set to be larger than the belt radius Rb which is the radius of the outer surface in the radial direction of the belt layer.

As a result, the value of the displacement D'in the outer region can be increased and the camber thrust can be improved.

Further, in the invention of claim 2, the contact J is
It is located on the tread surface between the 1/3 point that separates 1/3 times the tread half-width WT / 2 from the tire equator point and the 2/3 point that separates 2/3 times, and the position of the contact point J is It is characterized in that a circumferential groove extending in the circumferential direction of the passing tire is formed.

The tread rigidity is reduced by the circumferential groove, and the displacement D'in the outer region, which is outside the circumferential groove in the tire axial direction, can be further changed.

Further, in the invention of claim 3, the tread rubber has a gradually increasing region in which the thickness gradually increases outward in the tire axial direction, and the tread portion has a tread range centered on the tire equator and the carcass. And a belt layer formed between the belt layer and the belt layer, the cushion layer being formed of cushion rubber having a rubber hardness lower than that of the tread rubber and having a thickness reduced toward the outer side in the tire axial direction.

The cushioning layer reduces the rigidity under the belt layer in the central region, so that the belt layer itself easily moves in the lateral direction in the central region. As a result, the displacement D'in the central region is relatively reduced, and the camber thrust can be further improved.

Further, in the invention of claim 4, the tread rubber comprises a base rubber layer on the belt layer side and a cap rubber layer on the tread surface side having a rubber hardness smaller than that of the base rubber layer. And the ratio of the rubber thickness Mb of the base rubber layer to the rubber thickness Mk of the cap rubber layer Mk / M
b is the average value (Mk / Mb) c in the central region is 70 /
30 or more, the average value (Mk / Mb) o in the outer region is 70 /
It is characterized by being less than 30.

As a result, the rigidity of the tread rubber in the central region is reduced as compared with that in the outer region. Therefore, even if the value of the displacement D ′ is the same, the lateral force generated from the central region can be made smaller and the lateral force generated from the outer region can be made larger, and as a result, the camber thrust can be further improved. .

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a pneumatic tire 1 of the present invention, which is formed as a light truck tire, is mounted on a regular rim, and is filled with an internal pressure of 50 kPa.
The meridional section in the 0 kPa internal pressure state is shown.

The "regular rim" is a rim that is defined for each tire in the standard system including the standard on which the tire is based. For example, JATMA is a standard rim, and TRA is "Design Rim". , Or ETRTO means “Measuring Rim”. Further, the tire under an internal pressure of 50 kPa has a small internal strain and a minimum deformation, and is close to the tire shape in a state where the tire is vulcanized and molded in the mold.

In the figure, a pneumatic tire 1 comprises a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 located at an inner end of each sidewall portion 3. And with. A carcass 6 is bridged between the bead portions 4 and 4, and a strong belt layer 7 is wound inside the tread portion 2 and outside the carcass 6.

The carcass 6 is exemplified by a case where one or more carcass plies 6A and 6B, in which carcass cords are arranged at an angle of 75 ° to 90 ° with respect to the tire circumferential direction, are formed in this example. ing. As the carcass cord, organic fiber cords such as nylon, polyester, rayon, and aromatic polyamide are preferably used, but steel cords may also be used depending on the size and category of the tire, or requirements.

Further, the carcass 6 is folded back from the inner side to the outer side around the bead core 5 and locked on both sides of the main body portion 6a extending from the tread portion 2 to the side wall portion 3 to the bead core 5 of the bead portion 4. It has a folded-back portion 6b. A bead apex rubber 8 is provided between the main body 6a and the folded-back portion 6b so as to extend outward from the bead core 5 in the radial direction of the tire.

In this example, the folded-back portion 6b has a so-called high turn-up structure in which the height of the radially outer end from the bead base line BL is larger than the height of the bead apex rubber 8 at the radially outer end. None, it cooperates with the bead apex rubber 8 to reinforce the bead portion 4 and enhance the tire lateral rigidity. When the carcass 6 is formed by a plurality of plies as in this example, it is preferable that at least one carcass ply has a high turn-up structure.

The belt layer 7 is composed of two or more, in this example, two belt plies 7A, 7 in which high elastic belt cords are inclinedly arranged at an angle of 10 ° to 35 ° with respect to the tire circumferential direction.
A case of being formed from B will be exemplified. Each belt ply 7
A and 7B are arranged in different directions so that the belt cords intersect each other between the plies. The triangle structure of the cords enhances the belt rigidity, and the tread portion 2 is reinforced with a hoop effect. To do. As the belt cord, a steel cord or a highly elastic fiber cord having strength close to steel, such as aromatic polyamide fiber or aromatic polyester fiber, is preferably used.

Further, in this embodiment, the inner belt ply 7A is formed to be slightly wider than the outer belt ply 7B to relieve the stress concentration acting on the outer end of the belt.

Further, in the present application, when the tread surface 2S is divided into a central region Yc on the tire equator C side and an outer region Yo outside thereof in the meridional section of the tire, this central region Yc
Average thickness Tc of the tread rubber 2G and the outer region Y
The thickness ratio Tc / To with the average thickness To of the tread rubber 2G at o is set to be smaller than 1 and larger than 0.75, whereby the tread radius Rt which is the radius of curvature of the tread surface 2S is set to Radial outer surface 7S of the belt layer 7
The radius of curvature is larger than the belt radius Rb.

Here, the central area Yc is a point at which a line segment X having an angle α of 6 ° with respect to the tire equator line CX and having the tread edge TE side inclined radially inward is in contact with the tread surface 2S ( When the contact point) is J, it means a region between the contact point J and the tire equator point C1. The outer region Yo means a region between the contact point J and the tread edge TE. Further, the tire equator line CX means a tire axial direction line passing through a point (tire equator point) C1 on the tread surface 2S in the tire equator C.

The average thickness Tc means the tread surface 2
It is the average of the thickness T between S and the radial outer surface 7S of the belt layer 7 in the central region Yc, and specifically, the average value (Tmax + Tmin) of the maximum value Tmax and the minimum value Tmin in the central region Yc. ) / 2. Therefore, even if the outer side of the belt layer 7 has a so-called band layer 9 formed by spirally winding an organic fiber cord such as nylon in the tire circumferential direction, the thickness T is equal to the thickness of the band layer 9. It will be the included value. Similarly, the average thickness To is the average of the thickness T between the tread surface 2S and the radial outer surface 7S of the belt layer 7 in the outer region Yo, specifically, in the outer region Yo. Maximum value Tmax and minimum value Tmi
The average value with n is (Tmax + Tmin) / 2. When the belt layer 7 is interrupted inside the tire axial direction with respect to the tread edge TE, the thickness T is measured using a virtual extension line of the outer surface 7S.

By the way, as is clear from FIG. 4 which shows a grounded state in which a camber angle is given, a point P due to grounding is applied.
It can be seen that the displacement D'between t'and Pb 'tends to increase as the thickness of the tread rubber increases.

Therefore, as in the present application, the thickness ratio Tc /
To is reduced to the range of 1.0 to 0.75 and tread rubber 2
By relatively increasing the average thickness To of the outer region Yo of G relative to the average thickness Tc of the central region Yc, the displacement D ′ itself in the outer region Yo can be increased, and the camber The thrust can be increased to the plus side, that is, the camber thrust can be improved.

At this time, if the tread radius Rt is increased, the wandering performance is deteriorated by this, so that the effect of improving the camber thrust of the present application cannot be effectively exhibited. Therefore, the tread radius Rt
Is the same as that of the conventional tire, that is, the belt radius Rb is wider than that of the conventional tire while maintaining 3.8 to 5.1 times the tread half width WT / 2 which is the distance from the tire equator C to the tread edge TE. The thickness ratio Tc / To
Needs to be set in the range of 1.0 to 0.75.

When the thickness ratio Tc / To is 1.0 or more,
The displacement D'cannot be secured sufficiently large, and the camber thrust becomes too small. On the contrary, at 0.75 or less,
As a result, the cornering force is reduced and the steering stability is reduced. Therefore, the thickness ratio Tc / To is preferably 0.9 or less.

Here, the reason why the angle α of the line segment X for defining the contact point J which is the boundary between the central region Yc and the outer region Yo is set to 6 ° is that it is used for a passenger car tire or a light truck tire. This is because the camber angle θ at which ruts become a problem is usually about 6 °. Therefore, the displacement D'in the outer region Yo determined by the angle α of 6 °
By increasing the, the wandering performance is improved according to actual vehicle driving.

However, even if the displacement D'in the outer region Yo increases, if the area of the outer region Yo is small, the effect of improving the camber thrust also becomes small. Therefore, in order to secure the area of the outer region Yo as a minimum, the contact point J is set to 1/3 point that separates 1/3 times of the tread half width WT / 2 from the tire equatorial point C1 as shown in FIG. 2/3 points J2 separating J1 and 2/3 times
It is preferable to be located between and.

At this time, it is preferable to form a tread groove including the circumferential groove 10 extending in the tire circumferential direction through the position of the contact J on the tread surface 2S. The circumferential groove 10 divides the blocks in the outer region Yo and the central region Yc and makes it easier to deform in the outer region Yo, so that the displacement D ′ can be further increased. In such a case, as shown in FIG. 3, the angle βA with respect to the normal line on the tread surface of the groove wall surface 10A on the central region Yc side of the circumferential groove 10 is set on the tread surface of the groove wall surface 10B on the outer region Yo side. It is preferable that the angle is smaller than the angle βB with respect to the normal line.

Next, in the tread rubber 2G, in order to prevent the thickness T from abruptly changing between the central region Yc and the outer region Yo to deteriorate the grounding property and the uneven wear resistance, It is preferable to include a gradually increasing region V in which the thickness gradually increases toward the outer side in the tire axial direction. This gradual increase area V is as in this example.
It is preferable to form at least the central region Yc.

In the present example, the tread rubber 2G is
In the case where the base rubber layer Gb on the belt layer 7 side and the cap rubber layer Gk on the tread surface 2S side having a rubber hardness Hsk smaller than the rubber hardness Hsb of the base rubber layer Gb are formed in a two-layer structure. To illustrate. This base rubber layer G
The rubber hardness Hsb of b is 64 to 70 degrees, and the cap rubber layer G is
It is preferable that the k has a rubber hardness Hsk of 62 to 68 degrees, and the rubber hardness difference (Hsb-Hsk) is 2 degrees or more. As a result, the soft cap rubber layer Gk ensures excellent grounding and gripping properties, while the hard base rubber layer Gb can exhibit excellent steering stability and rolling performance.

At this time, the ratio M between the rubber thickness Mb of the base rubber layer Gb and the rubber thickness Mk of the cap rubber layer Gk.
In this example, k / Mb is the average value (M
k / Mb) c is 70/30 or more, and the average value (Mk / Mb) o in the outer region Yo is less than 70/30.

As a result, the rigidity of the tread rubber 2G in the central region Yc is reduced as compared with the outer region Yo. As a result, even if the value of the displacement D ′ is the same, the lateral force generated from the central region Yc can be made smaller and the lateral force generated from the outer region Yo can be made larger, and the camber thrust can be further improved. Is possible. Therefore, it is more preferable that the average value (Mk / Mb) c is 65/35 to 55/45 and the average value (Mk / Mb) o is 75/25 to 90/10.

Further, in this embodiment, the tread portion 2 has a thickness in the range of the tread portion 2 centered on the tire equator C and between the carcass 6 and the belt layer 7 toward the outer side in the tire axial direction. A buffer layer 11 made of cushion rubber 11G that reduces t1 is provided. This cushion rubber 1
1G is smaller than the rubber hardness Hst of the tread rubber 2G,
When the tread rubber 2G has a two-layer structure as in this example, it is made of a soft rubber smaller than the base rubber layer Gb, preferably smaller than the cap rubber layer Gk. At this time, the difference between the rubber hardness Hsc of the cushion rubber 11G and the rubber hardness Hst or Hsb or Hsk is preferably 5 degrees or more.

The rubber hardness is JIS-K6 in the present application.
It is defined as hardness according to durometer type A according to 253.

This buffer layer 11 (cushion rubber 11G)
Reduces the rigidity under the belt layer 7 in the central region Yc. Therefore, the belt layer 7 itself easily moves in the lateral direction especially in the central region Yc. As a result, the central area Y
The displacement D ′ at c is relatively reduced, and the camber thrust can be further improved.

Therefore, it is preferable to secure a thickness t1max of the buffer layer 11 at the tire equator of 2.0 mm or more. However, when the thickness t1max is excessively large, the amount of movement of the belt layer 7 increases, leading to deterioration in steering stability and rolling performance. Therefore, the upper limit of the thickness t1max is preferably set to 5.0 mm.

In the present application, the average thickness Tc of the tread rubber 2G in the central region Yc is relatively low.
In the central region Yc, the envelope effect and the riding comfort tend to decrease, but the rigidity relaxation by the buffer layer 11 can compensate for this and improve. Therefore, it is preferable that the buffer layer 11 has substantially the same width as the gradually increasing region V and is formed so as to oppose the gradually increasing region V.

Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be carried out in various modes such as a tire for a passenger car.

[0047]

EXAMPLES A small truck tire having a tire size of 205 / 70R16 and a structure shown in FIG. 1 was prototyped according to the specifications of Table 1, and the camber thrust CT and uneven wear resistance of each trial tire were tested. did.

(1) Camber thrust CT Using a maneuverability tester (flat belt tester), rim (51/2), internal pressure (600 kPa), load (10.6)
under the condition of kN)
Versal thrust was measured.

(2) Uneven wear resistance Test tires were attached to all wheels of a small truck, and the tires were run on an ordinary road and a highway for a total of 3000 km, and the circumferential groove 10 was used.
The difference in the amount of wear between the inner side and the outer side in the tire axial direction was measured.

[0050]

[Table 1]

[0051]

Since the present invention is constructed as described above,
The displacement itself in the outer region can be increased, the camber thrust can be improved, and the wandering performance can be improved without changing the tread radius and tread width.

[Brief description of drawings]

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

FIG. 2 is an enlarged sectional view showing a tread portion thereof.

FIG. 3 is a cross-sectional view showing a circumferential groove.

FIG. 4 is a diagram illustrating a camber thrust generation mechanism.

FIG. 5 is a diagram illustrating a conventional technique.

[Explanation of symbols]

2 tread section 2G tread rubber 2S tread surface 3 Side wall part 4 bead part 5 bead core 6 carcass 7 Belt layer 7S Radial outer surface 10 circumferential groove 11 Buffer layer 11G cushion rubber CX tire equatorial line Gb base rubber layer Gk cap rubber layer TE tread edge V gradually increasing area X-ray segment Yc central area Yo outside area

Claims (4)

(57) [Claims] 1. A pneumatic tire comprising a carcass extending from a tread portion to a side wall portion to a bead core of a bead portion, and a belt layer disposed inside the tread portion and radially outside the carcass. There is 6 ° to the tire equator in the tire meridian section
Of the tread rubber between the tread surface and the radial outer surface of the belt layer, having a contact point J in which a line segment whose tread edge side is inclined inward in the radial direction contacts.
The average thickness T in the central region between the contact point J and the tire equator point
The ratio Tc / To between c and the average thickness To of the outer region between the contact point J and the tread edge is less than 1 and 0.75.
By setting the tread radius Rt, which is the radius of the tread surface in the cross section, to be larger than the belt radius Rb, which is the radius of the radially outer surface of the belt layer. tire. 2. The contact point J is a 1/3 point that separates 1/3 times the tread half width WT / 2 from the tire equator point, and 2 /
The pneumatic tire according to claim 1, wherein a circumferential groove is formed which is located on a tread surface between two-third points which are three times apart and which extends in the tire circumferential direction through a position of the contact point J. . 3. The tread rubber has a gradual increase region in which the thickness gradually increases outward in the tire axial direction, and the tread portion has a tread range centering on the tire equator, and the carcass and the belt layer. The pneumatic tire according to claim 1 or 2, further comprising: a cushioning layer having a cushion rubber having a rubber hardness lower than that of the tread rubber and having a thickness reduced outward in the axial direction of the tire. 4. The tread rubber comprises a base rubber layer on the belt layer side and a cap rubber layer on the tread surface side having a rubber hardness smaller than the rubber hardness of the base rubber layer,
Further, the ratio Mk / Mb of the rubber thickness Mb of the base rubber layer and the rubber thickness Mk of the cap rubber layer is 70/30 or more in the average value (Mk / Mb) c in the central region, and in the outer region. The pneumatic tire according to any one of claims 1 to 3, wherein the average value (Mk / Mb) o is less than 70/30.