JPH05338416A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve abrasion resistance and deflected abrasion resistance by making groove depth of a groove positioned in an outside region shallower than groove depth of a groove positioned in an inside region as well as making a negative ratio in the outside region smaller than a negative ratio in the inside region. CONSTITUTION:A pneumatic tire 11 is constituted by forming a plural number of grooves 34 on the road surface of a tread part linking a pair of side wall parts 14 with each other and arranging a sponging rubber layer 29 having independent bubbles. When this tread part 15 is divided into four in the axial direction and two regions making contact with tread ends 36, 37 are made as outside regions 38, 39 and two regions making contact with a tread center 40 are made as inside regions 41, 42, a negative ratio in the outside regions is made to be smaller than a negative ratio in the inside regions and simultaneously, groove depth Ds of a groove positioned in the outside regions is made to be shallower than groove depth Du of a groove positioned in the inside regions. Additionally, width W of the tread part 15 is made to be within a range of 0.65 time to 0.75 time of the tire maximum width B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a foam rubber layer arranged on the tread surface of a tread portion.

[0002]

2. Description of the Related Art Conventionally, there have been various pneumatic tires which have high ice and snow performance, that is, driving, braking, and steering performance when traveling on an ice and snow road surface, and which can prevent generation of dust when driving on a dry road surface. There has been proposed one in which a foam rubber layer having closed cells is arranged on the tread surface of the tread portion.

[0003]

However, in such a conventional pneumatic tire, since the entire tread surface of the tread portion is made of foamed rubber having low rubber hardness (low rigidity), the dry road There is a problem in that the foamed rubber layer is greatly deformed during traveling, which causes the foamed rubber layer to wear early. Moreover, when the tread pattern of the pneumatic tire is a lug type or a block type, the amount of slippage with respect to the road surface of the block located at the tread end, the end on the kick side of the lug, is increased by the large deformation as described above. It becomes significantly larger than the amount of slip at the end, uneven wear called heel and toe wear occurs at the tread end at an early stage, and when the tread pattern of the pneumatic tire is a rib type, the large deformation occurs. As a result, the amount of slippage of the rib located at the tread end with respect to the road surface becomes significantly larger than the amount of slippage of the rib located at the center of the tread with respect to the road surface, and uneven wear called shoulder drop wear occurs at the tread end early. There are also problems.

In order to solve such a problem, a base layer made of non-foamed rubber having a relatively high rubber hardness is arranged inside the foamed rubber layer in the radial direction, that is, between the foamed rubber layer and the belt layer. It has been proposed that the base layer improves the rigidity of the foamed rubber layer, especially the foamed rubber layer at the end of the tread, and thereby improves the wear resistance and uneven wear resistance to practical values. As the performance of the tires has been improved, tires having higher wear resistance and uneven wear resistance have been required.

An object of the present invention is to provide a pneumatic tire capable of improving wear resistance and uneven wear resistance without deteriorating ice and snow performance.

[0006]

This object is provided with a pair of bead portions, a pair of sidewall portions extending outward from the bead portions in a substantially radial direction, and a tread portion connecting the sidewall portions. In a pneumatic tire in which a plurality of grooves are formed on the tread surface of the tread portion and a foamed rubber layer having closed cells is arranged, the tread portion is divided into four equal parts in the axial direction, and two regions in contact with the tread end are formed. When the outer region and the two regions in contact with the tread center are defined as the inner region, the negative ratio in the outer region is smaller than the negative ratio in the inner region, and the groove depth of the groove located in the outer region is located in the inner region. It can be achieved by making the groove depth smaller than that of the groove to be used, and further, by setting the width of the tread portion in the range of 0.65 to 0.75 times the maximum tire width. Kill.

[0007]

Operation: It is assumed that the pneumatic tire described above is running on a dry road. Here, in this tire, while making the negative ratio of the outer region smaller than the negative ratio of the inner region, the groove depth of the groove located in the outer region is made shallower than the groove depth of the groove located in the inner region. Therefore, the volume of the land portion of the outer region is larger than that of the land portion of the inner region, and the length in the radial direction is shorter. As a result, the rigidity of the land portion in the outer region is increased, and the inner region sandwiched by the outer region is also affected by the improvement in the rigidity of the outer region, and the rigidity is also increased. For this reason, the rigidity of the foamed rubber layer as a whole becomes high, it becomes difficult to deform, and the wear resistance is improved. In addition, this tire has a wider tread width than the conventional tire with a tread width in the range of 0.65 to 0.75 times the maximum tire width, increasing the contact area, further improving wear resistance. To do. Further, when the tread pattern of the pneumatic tire is a lug type or a block type, as described above, the rigidity of the land portion (lug or block) in the outer region is increased and the deformation amount is reduced, so that the tread pattern is reduced. The lugs located at the ends, the amount of slippage at the kick-out end of the block is reduced to suppress heel and toe wear, and even when the pneumatic tire has a rib type tread pattern, the tread ends The amount of slippage of the land portion (rib) located at is small and shoulder drop wear is suppressed. On the other hand, the ice and snow performance of this tire decreases as the groove depth in the outer region becomes shallow, but on the other hand, the negative contact ratio of the outer region decreases to increase the ground contact area.
It hardly changes.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2, reference numeral 11 denotes a pneumatic tire. The tire 11 includes a pair of bead portions 13 in which beads 12 are embedded and a pair of sidewall portions 14 extending from the bead portions 13 toward the outer side in a substantially radial direction. And a substantially cylindrical tread portion 15 that connects the outer ends of the sidewall portions 14 in the radial direction, and each of these portions extends from one bead portion 13 to the other bead portion 13 in a toroidal carcass layer 18 Are reinforced by. Here, the widthwise both ends of the carcass layer 18 are folded back around the bead 12 from the axially inner side to the axially outer side. The carcass layer 18 is composed of at least one (here, one) carcass ply 20, and a large number of cords extending in the meridian direction (radial direction) are embedded in each carcass ply 20. A belt layer 25 composed of a plurality of (two in this case) belt plies 24 is arranged on the outer side of the carcass layer 18 in the radial direction. The book's non-stretchable cord is embedded. Then, these cords are inclined in the opposite directions in the adjacent belt plies 24, and as a result, the adjacent belt plies 24 intersect each other. A tread 28 is arranged on the outer side of the belt layer 25 in the radial direction. Here, in the conventional tire, the width W of the tread portion 15 is about 0.64 times the maximum tire width B, but in this embodiment, the value of W / B is larger than that of the conventional tire.
It is set to 0.65 or more. As a result, in this tire 11, the width W of the tread portion 15 is widened, the ground contact area is increased, and the wear resistance is improved. Here, if the W / B value exceeds 0.75, the ground contact length in the circumferential direction becomes too short and the snow and snow performance deteriorates. Therefore, the W / B value must be 0.75 or less. For this reason, the width W of the tread portion 15 is set to a range of 0.65 to 0.75 times the maximum tire width B.

The tread 28 is arranged on the outer side in the radial direction, that is, on the tread surface, and on the inner side in the radial direction of the foamed rubber layer 29, that is, between the foamed rubber layer 29 and the belt layer 25. And a base rubber layer 30. The foamed rubber layer 29 is composed of a foamed rubber having a large number of closed cells inside, and such a foamed rubber is formed by adding a foaming agent to a usual rubber compound and heating and pressing it according to a usual tire manufacturing method. It Meanwhile, the base rubber layer 30
Is composed of ordinary non-foamed rubber. In addition, the tread of this tread 28 has a plurality of circumferential grooves that are axially separated.
34 and a large number of lateral grooves 35 that intersect the circumferential grooves 34 and are separated in the circumferential direction, and a large number of block-shaped land portions 33 are formed on the tread surface of the tread 28 by these grooves 34, 35.
Is defined.

Here, the tread 28 is divided into four equal parts in the axial direction, is in contact with the tread ends 36, 37, and two regions located axially inward of the tread ends 36, 37 are divided into outer regions 38, 39. On the other hand, when the two regions that are in contact with the tread center 40 and are located on both axial outer sides of the tread center 40 are defined as inner regions 41 and 42, the negative ratio Ns in the outer regions 38 and 39 is set to the inner region. 41, 42
It is smaller than the negative ratio Nu. As a result,
The outer region 38, as compared to the land portion 33 in the inner region 41, 42,
The volume of the land 33 at 39 increases. As a result, the rigidity of the land portion 33 in the outer regions 38 and 39 is increased,
Moreover, the inner regions 41, 42 sandwiched between the outer regions 38, 39
Also, the rigidity is increased under the influence of the rigidity increase of the outer regions 38 and 39. For this reason, the rigidity of the foamed rubber layer 29 as a whole is increased and it becomes difficult for the foamed rubber layer 29 to be deformed. Here, the negative ratio is a numerical value in which the total area of the grooves 34 and 35 located within the unit area is expressed as a percentage when the unit area of the tread 28 is 100%. The value of the negative ratio Ns in the outer regions 38, 39 is preferably 0.85 to 0.95 times the value of the negative ratio Nu in the inner regions 41, 42. The reason is that if the value of Ns / Nu is less than 0.85, the width of the grooves 34, 35 becomes narrow and the drainage property deteriorates a little, while if the value of Ns / Nu exceeds 0.95. This is because the effects of improving the wear resistance and the uneven wear resistance are not sufficient.

Also, in this embodiment, the outer region 38,
The groove depth Ds of the grooves 34 and 35 located in 39 is shallower than the groove depth Du of the grooves 34 and 35 located in the inner regions 41 and 42. As a result, as compared with the land portion 33 in the inner region 41, 42, the outer region
The radial length of the land portion 33 at 38 and 39 becomes short (height is low). As a result, the rigidity of the land portion 33 in the outer regions 38, 39 is further increased, and the rigidity of the inner regions 41, 42 is further increased as described above, so that the rigidity of the entire foam rubber layer 29 is sufficiently increased. is there. From the above, the wear resistance of the tire 11 is certainly improved. And
When the tire 11 is a lug type or a block type, the land portion in the outer regions 38, 39 is as described above.
Since the rigidity of 33 (lugs and blocks) is increased and the amount of deformation is reduced, the amount of slippage at the kick-out side end of the land 33 located at the tread end is reduced and heel and toe wear is suppressed. Also, in the case of the rib type, the amount of slippage of the land portion 33 (rib) located at the end of the tread is reduced, shoulder drop wear is suppressed, and wear on the entire tread 28 is made uniform. The value of the groove depth Ds of the grooves 34, 35 in the outer regions 38, 39 is in the range of 0.85 times to 0.90 times the value of the groove depth Du of the grooves 34, 35 in the inner regions 41, 42. Is preferred. The reason is that if the value of Ds / Du is less than 0.85, the depth of the grooves 34, 35 becomes too shallow and the drainage property deteriorates a little, while the value of Ds / Du is 0.90.
If it exceeds, the effect of improving the wear resistance and the uneven wear resistance becomes insufficient. Regarding the ice and snow performance of the tire 11, the groove depth of the outer regions 38, 39 decreases and decreases, while the negative ratio of the outer regions 38, 39 decreases to increase the ground contact area, It does not change.

Next, a test example will be described. In this test, the negative ratio in both the outer and inner regions was 40%, the groove depths in the outer and inner regions were both 8.8 mm, and the width of the tread (126 mm) was A conventional tire with a maximum width (196 mm) of 0.64 times, a negative ratio of 35% in the outer area, a negative ratio of 40% in the inner area, and the groove depth of the groove located in the outer area is 7.9 mm, the inner A test tire having a groove depth of 8.8 mm located in the region and a width (143 mm) of the tread portion being 0.73 times the maximum tire width (196 mm) was prepared. Here, the size of each tire is P
195/75 R14 and the tread pattern was as shown in FIG. Next, each tire was filled with an internal pressure of 2.4 kg / cm ² and mounted on a passenger car with a displacement of 3000 cc, and when the outside temperature was -5 ° C, sudden braking was applied while running on ice at 40 km / h. Ice and snow performance was obtained by measuring the braking distance from the point where the brake was applied to the point where the brake was stopped. As a result, when the comparative tire had an index of 100, the test tire also had an index of 100 and there was no difference between the two. Here, the index 100 is 50m
Met. Further, after running 10,000 km on a pavement road by the passenger car equipped with each of the above-mentioned tires, the remaining depth of the groove at the end of the running was measured to determine the wear resistance of each tire. As a result, if the comparative tire has an index of 100,
The test tire had an index of 115, which was significantly improved in wear resistance. Here, the index 100 was 2.8 mm. Furthermore, on the paved general road with the passenger car equipped with the above-mentioned tires
After traveling 1000 km, measure the radial distance (heel and toe step amount) between the most outwardly protruding portion of the outer surface of the block located at the tread end and the kick-out side end, and measure each The uneven wear resistance of the tire was calculated. As a result, when the comparative tire has an index of 100, the test tire has an index of 30, which is a dramatic improvement in uneven wear resistance. here,
The index 100 was 1.8 mm.

[0013]

As described above, according to the present invention, the wear resistance and the uneven wear resistance can be improved without deteriorating the ice and snow performance.

[Brief description of drawings]

FIG. 1 is a meridian sectional view of a tire showing an embodiment of the present invention.

FIG. 2 is a development view of a tread portion.

[Explanation of symbols]

 11 ... Pneumatic tire 13 ... Bead part 14 ... Side wall part 15 ... Tread part 34, 35 ... Groove 36, 37 ... Tread edge 38, 39 ... Outer area 40 ... Tread center 41, 42 ... Inner area Ds ... Groove depth Du ... Groove depth W ... Width B ... Tire maximum width

Claims (3)

[Claims] 1. A pair of bead portions, a pair of sidewall portions extending substantially radially outward from the bead portions, and a tread portion connecting the sidewall portions to each other, wherein a plurality of grooves are formed on the tread surface of the tread portion. In the pneumatic tire in which a foamed rubber layer having closed cells is formed, the tread portion is axially divided into four equal parts, two regions in contact with the tread end are an outer region, and two regions are in contact with the tread center. When the region is the inner region, the negative ratio in the outer region is smaller than the negative ratio in the inner region, and the groove depth of the groove located in the outer region is shallower than the groove depth of the groove located in the inner region, and The pneumatic tire, wherein the width of the tread portion is in the range of 0.65 to 0.75 times the maximum tire width. 2. The value of the negative ratio in the outer area is 0.85 times the value of the negative ratio in the inner area.
The pneumatic tire according to claim 1, wherein the range is 95 times. 3. The pneumatic tire according to claim 1, wherein the groove depth of the groove located in the outer region is in the range of 0.85 to 0.90 times the groove depth of the groove located in the inner region.