JPH0159121B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of abnormal wear that occurs when heavy-duty radial tires for trucks and buses are used for front wheels, particularly abnormal wear that occurs on the tread near the shoulders. The above heavy-duty radial tires are generally reinforced with at least three steel belts and filled with an internal pressure of 3 kg/cm ² or more.

Conventionally, radial tires with high rigidity on the tread and soft sidewalls were used under high loads.
Moreover, when it is installed on a large car with a long overall length and the car turns, it will be affected by changes in the load distribution due to centrifugal force and deviations between the direction of the tread and the direction of travel of the car.
In particular, an increase in ground contact pressure and an increase in the amount of sideslip at the shoulder section of the front tire causes the shoulder section to wear more quickly, often causing abnormal wear on the shoulder section that is unique to radial tires.

In order to improve such abnormal wear of the shoulder portion of heavy-duty tires, improvements have been made to the shape of the tread crown, the radius of the tread crown, the position of the belt width within the tread, etc., but these are still insufficient.

Therefore, in this invention, we pay attention to the variation in the ground pressure distribution of the tread and the deformation from the tread to the shoulder when the car turns, and we aim to reduce the increase in the ground pressure at the shoulder and the deformation of the tread near the shoulder when the car turns. The aim is to eliminate abnormal wear on the shoulder section by reducing this as much as possible.

In other words, the main tread part, which is in contact with the ground when the car is traveling straight, and the tread part, where the load is transferred due to centrifugal force when turning,
In order to prevent the ground contact pressure of the shoulder from increasing, an auxiliary tread part that makes contact with the ground during turning is provided, and the shape of the auxiliary tread part is different from that when the tire is new, i.e., when the grooves in the pattern of the tread part are deep and when turning. When the tread and shoulder parts are easily deformed due to changes in load due to centrifugal force, the auxiliary tread part contacts the ground even with a small lateral force, and the groove depth of the tread part at the end of running becomes shallow, causing the tread part and shoulder part to deform. When the tread becomes difficult to deform, a compound slope is formed in which the inclination angle of the auxiliary tread changes at the beginning and end of the tread wear so that the auxiliary tread contacts the ground with a larger lateral force than at the beginning of running. This was able to eliminate wear and tear.

Next, aspects of the present invention will be specifically described in detail based on drawings shown in examples.

FIG. 1-a shows an example of a cross section of a truck/bus tire commonly used in the past, and FIG. 1-b is a developed view showing the ground contact shape of the tread portion. Fig. 2-a shows an example of a cross section of a heavy-duty radial tire for explaining the working relationship between the main tread portion and the auxiliary tread portion.
b shows an example of the contact shape of the main tread portion and the auxiliary tread portion during turning.

FIG. 3-a is a partial cross-section of the main part showing the shape of the auxiliary tread portion of the present invention as a compound slope made of two different inclined straight lines, and FIG. 3-b is a partial cross-section of the main part of the auxiliary tread portion of the present invention. The shape is the intersection of two slope lines,
This is a partial cross-section of the main part showing compound slopes connected by circular arcs.

FIG. 4 is a cross-sectional view comparing the shape of the auxiliary tread portion between a single inclined surface and a compound inclined surface.

In the figure, FIG. 1 of a conventional example of a radial tire for trucks and buses shows a carcass ply 1 set in the radial direction, a belt layer 2 of breaker strips set at the lower part of the tread, a sidewall part 20 and It basically consists of a bead wire 3, a tread portion 4, four grooves 6 on the tread portion, and five ribs 7. In particular, the outer ribs are referred to as shoulder ribs _7S .

The tread portion of the tire of this invention is different from the conventional tread portion 4.
It is composed of a main tread surface portion 4M corresponding to the main tread surface portion 4M and an auxiliary tread surface portion 5 located continuously on the shoulder portion.

Next, the reason for this configuration will be explained.

Considering the running conditions of this vehicle, the approximate ground contact shape of the installed tires when traveling straight and when turning is as shown in Figure 1-b for conventional tires, when traveling straight:
When a tire touches the ground as shown by the solid line 8, when turning, the load moves to the outside of the turning radius, as shown by the dotted line 9, and the ground contact pressure of one shoulder increases in the ground contact shape along with the lateral displacement of the tire body. , the ground contact length also increases.

Furthermore, a lateral force due to centrifugal force acts on the tread portion, and the ribs 7 _S located outside the turning radius are slid and deformed in the lateral direction in the direction in which the width of the groove 6 narrows through contact with the ground. Due to this increase in ground contact pressure and skidding, the shoulder rib _7S wears out faster than other adjacent ribs 7, causing abnormal shoulder wear that is typical of radial tires.

In the tire of this invention, as shown in FIG.
The case where the auxiliary tread portion 5 is provided is investigated. That is, when the load is transferred to one shoulder part during turning, the auxiliary tread part contacts the ground, forming an increased ground contact part 10, and the width of the shoulder rib _7S substantially increases, and the ground contact area of the shoulder rib _7S increases. This increases the lateral stiffness of the shoulder rib 7 _S , suppressing the increase in the ground contact pressure per unit area of the shoulder rib 7 _S , and substantially increases the width of the shoulder rib 7 _S. Reduces deformation and skidding,
The aim is to eliminate abnormal wear on the shoulder rib _7S .

In addition, as mentioned above, when the tire is new, the grooves 6 are deep, so the ribs 7 and shoulder ribs _7S are easily deformed laterally due to lateral force, and as wear progresses, the ribs 7 and shoulder ribs _7S naturally deform. The auxiliary tread portion 5
It is necessary to form a plurality of composite slopes different from a single slope.

For example, when the product is new and prone to lateral deformation, a slope with a small angle is used, that is, at the contact points P _C between all side edges of the main tread section 4M and the auxiliary tread section 5,
It is selected within a small angle range of 25° to 45° with respect to the axis parallel to the axis of rotation of the tire.This varies somewhat depending on the usage conditions, but usually 30° to 35° is most suitable. . If this angle is smaller than 25°, the effect of reducing the increase in ground pressure due to the movement of the load during turning will be small; on the other hand, if this angle is larger than 45°,
Since the effect of supporting the load is small, the load is concentrated at the end of the main tread portion, and the effect of improving abnormal wear is small.

In addition, when the tread surface is worn out at the end of running, it becomes difficult to deform when force is applied to the ribs in the lateral direction. is 45°～
The angle should be selected within a large angle range of 65°, and usually about 50° to 55° is suitable. As mentioned above, the composite inclined surface of the auxiliary tread portion 5 is angled in the direction of the sidewall portion 20 within the range of 25° to 65° with respect to the axis parallel line RAL parallel to the rotational axis of the tire. It is to be selected. Outside this range, the effect of improving abnormal wear becomes smaller. In addition, the width from the contact point P _C between the auxiliary tread section and the main tread section to the contact point S _E between the side wall side end and the auxiliary tread section is from the axis parallel line RAL parallel to the rotation axis passing through P _C.
The height H from S to _E is at least the same as the groove bottom of the main tread. In other words, the contact point S _E between the end of the sidewall side and the auxiliary tread section is the intersection point on the extension line 11 extending the line connecting the bottom of the groove of the main tread section to the outer surface of the sidewall side of the tire, or below that point. Be present on the side. If the contact point of the S _E is located radially outward from the extension line 11, the abnormal wear prevention effect will be reduced, which is not preferable.

Note that the sidewall portion 20 is disposed following the contact point S _E between the side wall side end portion and the auxiliary tread portion, and the inclination angle of the sidewall portion with respect to the axis parallel line RAL at this contact point S _E is as follows. Conventional tires are usually more than 60 degrees, so if you extend it, it will be wider than a normal tire without an auxiliary tread.
A tire with an auxiliary tread section inclined toward the tread side with respect to the sidewall has a narrow main tread section, so in order to maintain the width of the main tread section, the inclination angle of the sidewall 20 with respect to the axis parallel line RAL is changed from the conventional one. It is considered to be larger than the tires.

An example of forming the composite slope of the auxiliary tread portion 5 is as shown in FIGS. 3-a and 3-b.

Figure 3-a shows the contact point between the main tread and the auxiliary tread.
The inclination angle of the inclination line of the auxiliary tread section 5 that inclines from P _C toward the sidewall section, that is, the small inclination angle (within the range of 25° to 45°) between the inclination line from the contact point P _C and the axis parallel line RAL. α ₁ , and the slope line of the auxiliary tread section that slopes diagonally upward from the contact point S _E between the side wall side end and the auxiliary tread section 5, that is, the contact point S _E
Let α ₂ be the large inclination angle (within the range of 45° to 65°) between the inclination line and the axis parallel line RAL, and support from the inclination line with the small inclination angle α ₁ and the inclination line with the large inclination angle α ₂ . This constitutes the tread portion 5.

In this embodiment, at the contact point P _C between the main tread surface portion 4M and the auxiliary tread surface portion 5, an inclined line 1 formed with the axis parallel line RAL is used.
The small inclination angle α ₁ of 3 is 35°, and the large inclination angle α ₂ of the inclination line 14 that is parallel to the axis at the contact point S _E
is 55 degrees, and the height of the auxiliary tread portion 5 is approximately the same as the depth of the groove 6 that ends at the contact point S _E between the extension line 11 of the line connecting the bottoms of the grooves 6 and the sidewall side edge of the outer surface of the tire. Or set to a higher range of heights.

The average inclination angle α ₀ through both angles α ₁ =35° and α ₂ =55° is 45°.

The drawing in Figure 3-a shows the different positions of the contact points S _E on the left and right sides of the same tire cross section for the purpose of showing that the contact points S _E are located at or below the intersection of the extension lines. .

In FIG. 3-b, in order to continuously increase the inclination angle of the auxiliary tread portion 5 from the beginning of the run to the end of the run,
At the contact point P _C between the main tread portion 4M and the auxiliary tread portion 5 in this embodiment, an inclined line 15 of α ₁ =30° is formed with respect to the axis parallel line RAL parallel to the rotation axis of the tire, and the side Contact point between wall side end and auxiliary tread
In S _E , an inclined line 16 of α ₂ = 60° is formed with respect to the axis parallel line RAL, and the intersection of both inclined lines is connected by an arc of radius R that is tangent to both inclined lines.
It is constructed so that the inclination angle at the intersection point increases smoothly, and the inclination angle α ₀ formed by the inclination line connecting the position of the contact point P _C and the position of the sidewall side edge S _E is 45°. It is composed of In addition,
At the contact point P _C between the main tread surface portion 4M and the auxiliary tread surface portion, the main tread surface portion and the auxiliary tread surface portion are separated by a ridge line.

The background of another advantage of forming a compound slope will be explained based on a comparison diagram of a single slope and a compound slope in FIG. 4.

First, the inclination angle of the auxiliary tread portion 5 required at the initial stage of driving.
If the range of 25° to 45° is set at the sidewall side end 18 which is the contact point with the extension line 11 of the line connecting the bottom of the groove 6 from the contact point 17 of the auxiliary tread part, that is, a single inclined surface When , as shown in FIG. 4, the thickness of the auxiliary tread portion at the sidewall side end 18 becomes extremely thick, which increases heat generation when the tire is running, and reduces the durability of the belt layer 2. In addition, unnecessary rubber increases the weight of the tire.

For example, in FIG. 4 for a 10.00R20, 14PR tire, if a single slope is formed by a slope line that passes through the contact point 17 of the auxiliary tread and has a slope angle α ₁ of 35°, then the sidewall side end 18 position thickness
T ₁ is 34 mm, whereas if it is formed into a composite inclined surface by the method shown in Figure 3-b, that is, contact 1 is
At position 7, the inclination line of α ₁ = 30° is the tangent line, and at the position of the sidewall side end 19, the inclination line of α ₂ = 60° is the tangent line, and the contact point 17 and the sidewall side end 19
When the inclination angle α ₀ with respect to the position is set to 45°, the thickness T ₂ at the position of the sidewall side end 19 becomes 28 mm, which can be reduced by about 18°C due to the heat generated by the tire when running. We were also able to reduce the weight of the tires by 2.3kg. In this way, by setting the compound slope with the necessary slope from the beginning to the end of the run, we were able to increase the durability compared to a single slope and improve the abnormal wear of the shoulder. It is.

The purpose of the radial groove or cut 12 in the buttrest part is to improve the heat dissipation of the shoulder part, but if this appears at the edge of the tread and makes contact with the ground, the radial groove or cut 12 will continue to contact the ground throughout the time of ground contact. The rubber on the tread surface in the vicinity becomes easy to move, causing abnormal wear from the radial groove or cut 12 portion. Therefore, in order to avoid contacting the ground in a state where abnormal wear is likely to occur in the radial groove or notch 12 at the initial stage of travel,
Contact point S _E between the extension line 11 of the line connecting the bottoms of the grooves 6 and the sidewall side end of the tire outer surface and the auxiliary tread surface
It is necessary to form a groove or notch in the buttrest part so that it does not protrude too much upward.

Therefore, the position h of the radial groove or notch 12 in the buttrest portion that protrudes above the sidewall side end S _E is 30% of the depth D of the groove 6 in the main tread portion 4M. It shall be within the following.

The 10.00R20, 14PR tires in the above example have grooves of 6
depth D = 14 mm, average inclination angle α ₀ is 45°, cutting depth Cd of the groove 12 in the radial direction of the buttrest part = 7 mm,
The position h of the groove 12 in the radial direction of the buttress is 4 mm. This α ₁ = 30° slope line, α ₂ = 60° slope line, and a tire that connects the intersection of both slope lines with a radius of 60 mm, abnormal wear of the shoulder is different from the timing of abnormal wear of conventional tires. The tire wear coefficient has been improved by 1.5 to 2.0 times, and at the same time the tire wear coefficient has also been improved by 15% to 40%.
This is something that could be improved.

[Brief explanation of drawings]

Fig. 1-a is a sectional view showing an example of a conventional heavy-duty radial tire, Fig. 1-b is a developed view showing the ground contact shape, and Fig. 2-a is a cross-sectional view showing an example of a conventional heavy-duty radial tire. 2-b is a cross-sectional view of a heavy-load radial tire for explaining the working relationship, FIG. 2-b is a diagram of the ground contact shape of the main tread portion and the auxiliary tread portion during turning, and FIG. 3-a is the auxiliary tread portion of the present invention. FIG. 3-b is a cross-sectional view of a composite inclined surface whose shape is composed of two different inclined straight lines,
A cross-sectional view of a compound inclined surface in which the shape of the auxiliary tread portion of the present invention is a curved surface in which the intersections of inclined lines are connected by circular arcs,
FIG. 4 is a comparative sectional view of a single inclined surface and a compound inclined surface constituting the auxiliary tread portion. 4M...Main tread part, 5...Auxiliary tread part, RAL
...Axis parallel line, 20...Side wall part, 6...
...Groove, D...depth of groove 6, 11...extension of the line connecting the bottoms of the grooves, 12...radial groove or cut in the buttrest part, h...radial groove or cut in the buttrest part, Position of the notch, P _C ...Contact point between the main tread and auxiliary tread, S _E ...Contact point between the auxiliary tread and the end of the sidewall.

Claims (1)

[Claims] 1. A radial tire for trucks and buses,
The tread part consists of a main tread part including the center part and an auxiliary tread part located in the shoulder part, and the contact point S _E between the auxiliary tread part and the sidewall side end is a line connecting the bottom of the groove of the main tread part. exists at or below the intersection of the extended line extended to the outer surface of the sidewall side of the tire, and from the contact point P _C of the main tread part and the auxiliary tread part, the auxiliary tread part slopes toward the sidewall part. An auxiliary tread portion whose inclination angle α ₁ of the inclination line is an angle selected within the range of 25° to 45° with respect to the axis parallel line parallel to the tire rotation axis, and which is inclined obliquely upward from the contact point S _E. The inclination angle α ₂ of the inclination line is an angle selected within the range of 45° to 65° with respect to the axis parallel line, and the auxiliary tread portion is always set so that the inclination angle α ₁ < inclination angle α ₂ A radial tire for heavy loads that improves abnormal wear when using the front wheels. 2 The inclination angle α ₁ of the slope line of the auxiliary tread part that slopes toward the sidewall part from the contact point P _C between the main tread part and the auxiliary tread part is 25° to 45° with respect to the axis parallel line parallel to the tire rotation axis. The inclination line of the angle selected within the range of ° and the inclination angle α ₂ of the inclination line of the auxiliary tread section that slopes diagonally upward from the contact point S _E of the auxiliary tread section and the side edge of the side wall are axis parallel lines. At the intersection of the slope line at an angle selected within the range of 45° to 65°, the slope is connected with an arc of radius R that is tangent to both slope lines to smoothly increase the slope angle at the intersection. A heavy-duty radial tire with improved abnormal wear according to claim 1, which is configured to increase abnormal wear. 3. Claims 1 or 2, in which the position h of the radial groove or notch in the buttrest part, which is set from the auxiliary tread part toward the sidewall part, is within 30% of the depth of the groove in the main tread part. A heavy-duty radial tire with improved abnormal wear as described in the section.