JPH04126607A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cracks in groove bottoms by arranging projecting strips in both of right and left sides of rubber thin films in lug grooves, shouldering tensile strength in the circumferential direction of a tire by means of these projecting strips, and preventing the tensile strength from acting on the rubber thin films. CONSTITUTION:Main grooves 2 extending in the circumferential direction of a tire and lug grooves 3 crossing those grooves are arranged on a tread 1, and blocks 6 are partitioned thereby. In the lug grooves 3 arranged so as to cross split positions X of a forming metal mold in both of right and left shoulder parts, rubber thin films 7 are formed so as to correspond to the split positions X. In this case, projecting strips 8 are formed respectively on both of right and left sides of the rubber thin films 7 in groove bottoms of the lug grooves 3. By the way, since the upper edges of the rubber thin films 7 are ruptured by the bending deformation in the tread, its crack advances gradually toward the groove bottoms of the lug grooves 3. Accordingly, by stopping almost its advancement at the vicinity of the upper edges of the projecting strips 8, for example, at a position P, its further advancement can be prevented.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a pneumatic tire, and more particularly to a method for preventing cracks in the bottom of lug grooves caused by rupture of a thin rubber film formed at the split position of a molding die. Regarding pneumatic tires designed to

[Conventional technology]

Among the molds used for molding pneumatic tires, sectional molds are a combination of two annular plates on the left and right for sidewall molding and sectors for tread molding that are divided into multiple parts in the tire circumferential direction. It consists of Insert a green tire into such a mold,
When a balloon-like bladder is inflated from inside and pressed against the inner surface of the mold, the internal pressure causes some of the unvulcanized rubber to flow into the joint between the sector and the annular plate, forming the tire. A thin rubber film may remain afterwards.

In the above-mentioned sectional mold, the sector and the annular plate are placed on the side of the shoulder (shoulder split) or on the tread side of a part of the shoulder (claran split). However, in the latter case of crown splitting, the above-mentioned molded rubber thin film is formed on the tread surface. However, when such a thin rubber film is formed in the lug grooves on the tread surface, it breaks while the tire is running, causing cracks to reach the bottom of the lug grooves and grow further, causing the grooves of the lug grooves to grow. This may cause cracks to form on the bottom.

Figures 4 and 5 show the main parts of a radial tire molded using the above-mentioned crown split sectional mold. 1
is a tread, 2 is a main groove extending in the circumferential direction of the tire, 3 is a lug groove that intersects the main groove, 4 is a belt layer provided within the tread,
5 is a carcass. The sector S and the annular plate P of the mold for molding such a radial tire have their split position X located on the crown side of a part of the shoulder as shown in the figure.
It extends in the tire circumferential direction so as to cross the lug groove 3.

Because of this configuration, there is a split position X in the lug groove 3.
A rubber thin film 7 is formed correspondingly, and the rubber thin film 7 connects the front and rear blocks 6.6 in the tire circumferential direction.

When a tire with such a thin rubber film runs on a road surface under load, the outer periphery of the tire nod rotates while deforming the ground contact surface that contacts the road surface and the portions before and after the ground contact surface. In other words, on the ground contact surface, the outer periphery of the tore throat concave inward and the radius of curvature becomes larger, whereas immediately before stepping in and immediately after kicking up, the outer periphery swells outward and the radius of curvature becomes smaller.
This means that it is constantly undergoing bending deformation.

Due to such bending deformation, compression and tension alternately act on the tread 1 in the tire circumferential direction E-E, and the upper end of the rubber thin film 7 breaks due to the tensile tension at that time, and the crank C gradually becomes lug. It progresses toward the bottom of the groove 3 and eventually reaches the bottom of the groove. In this way, when the crank C of the thin rubber film reaches the groove bottom, the groove bottom is in the same state as if a small scratch had been given to it, so stress is concentrated on the scratch due to the repeated action of compression and tension, and the groove This will create a crank at the bottom. The crank at the bottom of the groove eventually reaches the belt layer.

This racking phenomenon becomes more noticeable when the splitting position is placed near the end of the belt layer, as in the case of a sectional mold for crown splitting. This is because the bending deformation is suppressed by the rigidity of the belt layer at the position where the belt layer is present, but the bending deformation becomes thicker in the end region where the belt layer is not present. Also, this phenomenon occurs when the driven wheel (front wheel)
This phenomenon is more noticeable in tires mounted on the drive wheels (rear wheels) than in tires mounted on the rear wheels. In the case of drive wheels, this is not only due to bending (shearing force also acts), but -
This is because severe forces act on the tread in a complex manner.

Conventionally, as a countermeasure to prevent cranking of the lug grooves as described above, there has been a proposal to enlarge the entire groove bottom. However, such measures reduce the drainage performance when driving on wet roads because the lug grooves become shallow, and the snow chewing performance when driving on snowy and icy roads, resulting in poor braking performance and driving performance on these roads. It will make your sexuality worse. Therefore, this proposal could not be said to provide an essential solution.

[Problem to be solved by the invention]

As mentioned above, it is an object of the present invention to prevent damage to the groove bottom of the lug groove from breaking of the rubber thin film formed at the split position of the molding die without adversely affecting braking performance and drive performance on wet roads or snowy and icy roads. An object of the present invention is to provide a pneumatic tire that does not cause cranking.

[Means to solve the problem]

To achieve the above object, the present invention provides a tire in which lug grooves are provided on the tread surface, and a thin rubber film is formed in the lug grooves in correspondence with the positions of the molding mold in the circumferential direction of the tire. The present invention is characterized in that protrusions are formed along both left and right sides of the rubber thin film.

In this way, the protrusions provided on both the left and right sides of the rubber thin film have the function of supporting the tensile force generated in the tire circumferential direction due to bending deformation of the tread. It is possible to prevent the above-mentioned tensile force from substantially acting on the material. Therefore, cracks generated in the rubber thin film progress to the vicinity of the protrusions, but do not grow further toward the bottom of the lug groove.

Hereinafter, the present invention will be specifically explained with reference to embodiments shown in FIGS. 1 to 3.

FIG. 3 shows a part of the tread surface of the radial tire of the present invention. Similar to the explanation of the conventional tire shown in FIGS. 4 and 5, 1 is a tread, 2 is a main groove of the tread 1 extending in the circumferential direction of the tire, 3 is a lug groove that intersects this main groove 2, and 6 is a main groove of these main grooves. 2 and a lug groove 3. Further, X indicates a position corresponding to the position where the sector and the annular plate of the sectional mold mentioned above are divided.

The split position of the molding die in a part of both the left and right shoulders
As shown in detail in FIG. 1.2, a rubber thin film 7 is formed in each of the lug grooves 3 arranged to traverse the gap, corresponding to the split position X. This rubber thin film 7 extends in the tire circumferential direction EE, and has both ends integrally connected to the front and rear blocks 6.6, and its lower end integrally connected to the groove bottom of the lug groove 3.

Further, at the bottom of the lug groove 3, protrusions 8, 8 are formed on both left and right sides of the rubber thin film 7, respectively. This protrusion 8
extends in the tire circumferential direction along the rubber thin film 7, and has both front and rear ends integrally connected to the inner wall of the block 6. As shown in FIG. 1, this protrusion 8 protrudes from the groove bottom to form a smooth convex shape in the radial cross section of the tire, and both front and rear ends are tangential to the inner walls of the front and rear blocks 6. It is connected. This shape prevents stress from being concentrated when subjected to bending deformation.

When a pneumatic tire as described above runs on a road surface, the tread undergoes repeated bending deformation as described above. Due to this bending deformation, the upper end of the rubber thin film 7 breaks due to the tensile force in the circumferential direction of the tire, and the crack gradually advances toward the bottom of the lug groove 3. However, its progress almost stops at, for example, two points near the upper edge of the protrusion 8 (see FIG. 1), and does not progress any further. That is, the crank of the rubber thin film 7 never reaches the bottom of the lug groove 3.

The reason why the crank is prevented from progressing in this way is that the tensile force generated in the circumferential direction of the tire due to bending deformation of the tread is carried by the ridges 8 on both the left and right sides, and at least the ridges are applied to the rubber thin film 7. This is because it hardly acts in the area corresponding to 8,8.

In order to further improve the effect of supporting the tensile force by the protrusion 8, the height a of the protrusion 8 from the bottom of the lug groove should be set to 10 to 30% of the depth D of the lug groove 3. , and the distance from the rubber thin film 7 to the height a of the protrusion 8.
It is good to make it 1.5 times or less, preferably 0.5 to 1.2 times. Furthermore, as shown in FIGS. 1 and 2, the cross section of the protrusion 8 in the tire radial direction is made into a smooth curved shape formed by combining one or more circular arcs, and furthermore, the front and rear blocks 6
It is also best to make the connection to a smooth tangential line.

Furthermore, since the above-mentioned pneumatic tires only have small protrusions on the bottom of the lug grooves, there is no negative effect on drainage performance or snow chewing performance, and braking performance and driving performance on wet roads or snowy and icy roads. There is no reduction in sexuality.

In addition, in the above-mentioned embodiment, a case where a pneumatic tire is molded using a sectional mold was explained, but the present invention is not limited to this, and a two-split mold having a split position in a part of the tread center is used. It can be similarly applied to pneumatic tires that use a rubber film, since a thin rubber film is generated at the split position. Moreover, it can be applied not only to radial tires but also to bias tires.

(Example) A pneumatic radial tire (tire of the present invention) having a tread pattern as shown in Fig. 3 and a tire size of 100 OR 20 was vulcanized using a crown-split sectional mold. The depth of the lug groove D =
15ff++n, height of protrusion from lug groove a = 2.5
+no+, and the distance b from the rubber thin film was set to 2.5 mm.

On the other hand, as a comparative example, the third
A pneumatic radial tire (comparison tire) having the same tread pattern and the same tire size as shown in the figure was vulcanized and molded using the same crown-split sectional mold.

The above two types of tires were subjected to a drum test under the following conditions to examine the occurrence of cranking at the bottom of the lug grooves having a thin rubber film.

As a result, in the tire of the present invention, although the rubber thin film was broken, the lower end of the crack stopped near the upper edge of the ridge and did not reach the bottom of the lug groove. On the other hand, in the comparative tire, the crack formed by the rupture of the rubber thin film reached the bottom of the lug groove, and a crack with a depth of 5 mm was generated at the bottom of the lug groove.

<Drum test> The test tire was mounted on a rim with a rim size of 7.007 mm and filled with air at an air pressure of 7.25 kgf/cii, and the test tire was placed on a rotating drum with a diameter of 1707 mm at an initial load (JIS Regular load) After applying contact pressure of 2,700 kg and running for 11,000 km at a constant speed of 80 km/h, the load was increased by 270 kg and the vehicle was run for 11,000 km, and thereafter the load was increased by 270 kg until IQOO.
After repeating the operation of traveling 5000 km from the beginning until a total traveling distance of 5,000 km was reached, the degree of growth of cracks that had occurred in the rubber thin film was checked.

(Effects of the Invention) As described above, the pneumatic tire of the present invention has protrusions on both the left and right sides of the rubber thin film in the lug grooves, so the protrusions carry the tensile force in the circumferential direction of the tire, and the rubber It is possible to substantially prevent the above-mentioned tensile force from acting on the thin film.Therefore, the crank generated in the rubber thin film is suppressed from growing to the groove bottom of the lug groove, and the crank is prevented from occurring at the groove bottom. In addition, since the protrusions are simply provided, there is no negative effect on the drainage performance of the lug grooves or snow chewing performance, and there is no adverse effect on braking performance or drivability on wet roads or snowy and icy roads. Never.

[Brief explanation of drawings]

1 to 3 show a pneumatic tire according to an embodiment of the present invention. 1 is a side view of the main part of the tre-nod part as seen in the direction of arrow I in Fig. 1, and Fig. 3 is a plan view of the main part of the trend part. 4 and 5 show a conventional pneumatic tire, FIG. 4 is a radial cross-sectional view of a shoulder portion of the tire, and FIG. 5 is a schematic perspective view of an open portion ρ. 1... Tread, 2... Main groove, 3... Lug groove, 6
...Block, 7...Rubber thin film, 8...Protrusion. Agent Patent Attorney Nobuo Ogawa −

Claims (1)

[Claims] In a tire in which a lug groove is provided on the tread surface, and a thin rubber film is formed in the lug groove corresponding to the position of the molding die in the circumferential direction of the tire, a groove bottom of the lug groove is provided along both left and right sides of the thin rubber film. A pneumatic tire with ridges formed on each side.