JP3152368B2 - Pneumatic 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 tire in which a foamed rubber layer is disposed on a tread of a tread portion.

[0002]

2. Description of the Related Art Conventionally, various pneumatic tires having high snow and snow performance, that is, high driving, braking and steering performance when traveling on an ice and snow road surface, and capable of preventing generation of dust when traveling on a dry road surface are known. There has been proposed one in which a foamed rubber layer having closed cells is arranged on a tread surface of a tread portion, for example.

[0003]

However, in such a conventional pneumatic tire, the entire tread surface of the tread is made of foamed rubber having a low rubber hardness (low rigidity). There is a problem that the foamed rubber layer is greatly deformed during running, and thereby the foamed rubber layer is worn out early. Moreover, when the tread pattern of the pneumatic tire is a lug type or a block type, the amount of slip of the block located at the tread end and the trailing end of the lug on the road surface is reduced by the large deformation described above. If the tread edge becomes significantly larger than the amount of slip at the end, uneven wear called heel-and-toe wear occurs at an early stage, or if the tread pattern of the pneumatic tire is a rib type, the large deformation occurs. As a result, the amount of slip of the rib located at the end of the tread with respect to the road surface becomes significantly larger than the amount of slip 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 at an early stage. 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 disposed radially inside the foamed rubber layer, that is, between the foamed rubber layer and the belt layer. There has been proposed a vehicle in which the rigidity of the foamed rubber layer, particularly the foamed rubber layer at the end of the tread is improved by this base layer, thereby improving the wear resistance and uneven wear resistance to practical values. As the performance of tires has increased, tires having even higher wear resistance and uneven wear resistance have been required.

[0005] It is an object of the present invention to provide a pneumatic tire capable of improving wear resistance and uneven wear resistance without deteriorating ice and snow performance.

[0006]

SUMMARY OF THE INVENTION An object of this invention is to provide a pair of bead portions, a pair of sidewall portions extending substantially radially outward from the bead portions, and a tread portion connecting between 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 edge 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 positioned in the inner region. It is achieved by making the groove depth shallower than the groove depth of the groove to be formed, and further, by setting the width of the tread portion in the range of 0.65 times to 0.75 times the maximum width of the tire. Kill.

[0007]

Now, it is assumed that the pneumatic tire 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 in the outer region is larger than that of the land portion in 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 increases, and the rigidity of the inner region sandwiched between the outer regions also increases due to the effect of the improvement in the rigidity of the outer region. For this reason, the rigidity of the entire foamed rubber layer is increased, so that the foamed rubber layer is not easily deformed, and the wear resistance is improved. Furthermore, this tire has a tread width of 0.65 to 0.75 times the maximum width of the tire, making the tread wider than conventional tires and increasing the contact area, further improving wear resistance. You do it. 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 (the lug or the block) in the outer region is increased and the deformation amount is reduced. The lug located at the end, the amount of slip at the kick-out side end of the block is reduced to suppress heel-and-toe wear, and also when the tread pattern of the pneumatic tire is a rib type, the tread end The slip amount of the land portion (rib) located at the position is reduced, and the 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 shallower, but on the other hand, the contact area increases due to a decrease in the negative ratio in the outer region.
Hardly changes.

[0008]

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 has a pair of bead portions 13 in which beads 12 are embedded, and a pair of side wall portions 14 extending substantially radially outward from the bead portions 13. And a substantially cylindrical tread portion 15 connecting the radially outer ends of the sidewall portions 14 to each other. Each of these portions has a toroidal carcass layer 18 extending from one bead portion 13 to the other bead portion 13. Has been reinforced. Here, both ends of the carcass layer 18 in the width direction are folded around the bead 12 from the inside in the axial direction to the outside in the axial direction. The carcass layer 18 is composed of at least one carcass ply 20 (here, one carcass ply). In each carcass ply 20, a number of cords extending in the meridian direction (radial direction) are embedded. A belt layer 25 composed of a plurality of (two in this case) belt plies 24 is disposed radially outside the carcass layer 18, and a plurality of belt plies 24 inclined at a predetermined angle with respect to the circumferential direction are arranged in the belt plies 24. A non-extensible cord of the book is embedded. These cords are inclined in opposite directions in the adjacent belt plies 24, and as a result, cross each other between the adjacent belt plies 24. Further, a tread 28 is disposed radially outside the belt layer 25. Here, in the conventional tire, the maximum width W of the tread portion 15 is about 0.64 times the maximum width B of the tire, but in this embodiment, the value of W / B is larger than that of the conventional tire.
0.65 or more. As a result, in the tire 11, the width W of the tread portion 15 is increased, the contact area is increased, and the wear resistance is improved. Here, if the value of W / B exceeds 0.75, the contact length in the circumferential direction becomes too short and the ice / snow performance deteriorates. Therefore, the value of W / B must be 0.75 or less. For this reason, the width W of the tread portion 15 is set in a range of 0.65 to 0.75 times the maximum width B of the tire.

The tread 28 is disposed on the outer surface in the radial direction, that is, on the tread surface, and on the inner side in the radial direction of the foam rubber layer 29, that is, between the foam rubber layer 29 and the belt layer 25. And a base rubber layer 30. The foamed rubber layer 29 is made of foamed rubber having a large number of closed cells inside, and such foamed rubber is formed by adding a foaming agent to a usual rubber compound and heating and pressing according to a usual tire manufacturing method. You. Meanwhile, the base rubber layer 30
Is made of ordinary non-foamed rubber. The tread of the tread 28 has a plurality of circumferential grooves spaced apart in the axial direction.
34 and a number of lateral grooves 35 intersecting with the circumferential grooves 34 and spaced apart in the circumferential direction are formed, and by these grooves 34 and 35, a large number of block-shaped land portions 33
Is defined.

Here, the tread 28 is divided into four equal parts in the axial direction so that the tread ends 36 and 37 are in contact with the tread ends 36 and 37, and two regions located inside the tread ends 36 and 37 in the axial direction are outer regions 38 and 39. On the other hand, assuming that two regions that are in contact with the tread center 40 and are located on both outer sides in the axial direction of the tread center 40 are inner regions 41 and 42, the negative ratio Ns in the outer regions 38 and 39 is defined as an inner region 41, 42
Is smaller than the negative ratio Nu. As a result,
Outer region 38, compared to land 33 in inner regions 41, 42
The volume of the land 33 at 39 is increased. As a result, the rigidity of the land portion 33 in the outer regions 38 and 39 increases,
Moreover, the inner regions 41, 42 sandwiched between the outer regions 38, 39
Also, the rigidity is increased due to the effect of the improvement in the rigidity of the outer regions 38 and 39. For this reason, the rigidity of the entire foamed rubber layer 29 is increased, and it is difficult to deform. 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 defined as 100%. The value of the negative ratio Ns in the outer regions 38 and 39 is preferably in a range of 0.85 to 0.95 times the value of the negative ratio Nu in the inner regions 41 and 42. The reason for this is that if the value of Ns / Nu is less than 0.85, the width of the grooves 34 and 35 becomes narrow and the drainage becomes slightly worse, while if the value of Ns / Nu exceeds 0.95, This is because the effect of improving the wear resistance and uneven wear resistance is not sufficient.

In this embodiment, the outer region 38,
The groove depth Ds of the grooves 34 and 35 located at 39 is smaller than the groove depth Du of the grooves 34 and 35 located at the inner regions 41 and 42. As a result, the outer region is compared with the land portion 33 in the inner regions 41 and 42.
The length in the radial direction of the land portion 33 at 38 and 39 is short (the height is low). As a result, the rigidity of the land portion 33 in the outer regions 38 and 39 is further increased, and the rigidity of the inner regions 41 and 42 is further increased similarly to the above, and the rigidity of the entire foamed rubber layer 29 is sufficiently increased. is there. From the above, the wear resistance of the tire 11 is reliably improved. And
When the tire 11 is of a lug type or a block type, the land portions in the outer regions 38 and 39 are as described above.
Since the rigidity of the 33 (lugs and blocks) is increased and the amount of deformation is reduced, the amount of slip at the kick-out end of the land 33 located at the tread edge is reduced, and heel and toe wear is suppressed. Also, in the case of the rib type, the slip amount of the land portion 33 (rib) located at the end of the tread is reduced, so that the shoulder drop wear is suppressed, and the wear of the entire tread 28 is made uniform. In addition, the value of the groove depth Ds of the grooves 34 and 35 in the outer regions 38 and 39 is in a range of 0.85 to 0.90 times the value of the groove depth Du of the grooves 34 and 35 in the inner regions 41 and 42. Is preferred. The reason for this is that if the value of Ds / Du is less than 0.85, the depth of the grooves 34 and 35 becomes too shallow and the drainage performance is slightly deteriorated, while the value of Ds / Du is 0.90.
This is because, when the ratio exceeds 2, the effect of improving the wear resistance and uneven wear resistance becomes insufficient. In addition, regarding the ice and snow performance of the tire 11, while the groove depth of the outer regions 38 and 39 is reduced by being shallow, the contact area is increased by decreasing the negative ratio of the outer regions 38 and 39, so It does not change.

Next, test examples will be described. In this test, the negative ratio in both the outer region and the inner region was 40%, the groove depth in the outer region and the inner region was 8.8 mm, and the width (126 mm) of the tread portion was The conventional tire is 0.64 times the maximum width (196mm), the negative ratio in the outer region is 35%, the negative ratio in the inner region is 40%, and the groove depth in the outer region is 7.9mm. A test tire was prepared in which the groove located in the region had a groove depth of 8.8 mm, and the width of the tread portion (143 mm) was 0.73 times the maximum tire width (196 mm). 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. When the outside temperature was -5 ° C, running on ice at 40 km / h, sudden braking was applied. Ice and snow performance was determined by measuring the braking distance from the point where the brake was applied to the point where it stopped. As a result, assuming that the comparative tire has an index of 100, the test tire also has an index of 100 and there is no difference between the two. Here, the index 100 is 50m
Met. Further, after traveling 10,000 km on a general pavement road by the passenger car equipped with each tire described above, the remaining depth of the groove at the end of traveling was measured, and the wear resistance of each tire was determined. The result is that if the comparative tire has an index of 100,
In the test tires, the index of wear was 115 and the wear resistance was significantly improved. Here, the index 100 was 2.8 mm. In addition, the paved general road is
After traveling 1000 km, measure the radial distance (heel-to-toe step) between the most outwardly projecting part of the outer surface of the block located at the tread end and the kick-out side end. The uneven wear resistance of the tire was determined. As a result, assuming that the comparative tire had an index of 100, the test tire had an index of 30 and the uneven wear resistance was dramatically improved. here,
The index 100 was 1.8 mm.

[0013]

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

[Brief description of the drawings]

FIG. 1 is a meridian sectional view of a tire showing one 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 end 38, 39 ... outside area 40 ... tread center 41, 42 ... inside area Ds ... groove depth Du: groove depth W: width B: maximum tire width

Claims (3)

(57) [Claims] A pair of bead portions, a pair of side wall portions extending substantially radially outward from the bead portions, and a tread portion connecting between the side wall portions, and a plurality of grooves are formed on a tread surface of the tread portion. In the pneumatic tire in which 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 defined as an outer region and two regions 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 smaller than the groove depth of the groove located in the inner region. A pneumatic tire, wherein the width of the tread portion is in the range of 0.65 to 0.75 times the maximum width of the tire. 2. The method according to claim 1, wherein the value of the negative ratio in the outer region is set to 0.85 times the value of the negative ratio in the inner region.
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 a range of 0.85 to 0.90 times the groove depth of the groove located in the inner region.