JPH04310408A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To reduce the change of fall-out of each block in traveling on iced surface and prevent ground contact area of a tread surface from decreasing by forming the cross-section of cut grooves in tire circumferential direction in a funnel shape. CONSTITUTION:Four main grooves 10, 11, 12, and 13 are provided on the tread surface T in circumferential direction EE' of a tire and along the total periphery of the tire, and multiple auxiliary grooves 20 for connecting to the main grooves are also provided on it from one shoulder 14 to the other shoulder 14 in lateral direction of the tire to form multiple blocks 30. In each of the blocks 30, two cut grooves 40 are provided from one end of the block 30 to the other end in lateral direction to divide it into multiple sub-blocks 31, 32, and 33. The cross-section of each cut groove 40 in circumferential direction of the tire is formed in a funnel shape in which both groove are walls pushed out as protrusions. In the cut grooves 40, when a groove width at the bottom of the groove is t and a groove width on the surface of the tread is T, the equation T=2t to 6t must be satisfied, where t=0.4 to 1.5mm.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire with improved braking performance on icy road surfaces.

0002

[Prior Art] Conventionally, in order to improve braking performance on ice without placing studs on the tread surface, the number of minor grooves and grooves (sipes) arranged in the tire width direction on the tread surface was increased. The edge effect of these grooves was improved by increasing the edge effect of these grooves, and a rubber composition that did not harden even at low temperatures was used as the tread rubber to enhance the adhesion of the tread surface to the ice surface.

However, when the number of sub-grooves is increased, the ground contact area of the tread surface decreases, resulting in poor adhesion to the ice surface, which weakens the frictional effect with the ice surface and reduces braking performance. Furthermore, as the number of sub-grooves is increased, the interval between the sub-grooves becomes narrower, so when the tread surface M receives a braking force F while driving on ice as shown in FIG. 7, the blocks 4 move in the traveling direction as shown in FIG. In the opposite direction, the block 4 falls down from the position indicated by the dotted line to the position indicated by the solid line, and the ground contact area of the block 4 decreases.

Furthermore, when a plurality of cut grooves 3 are provided in the blocks 4 on the tread surface M as shown in FIG. 5, even if the number of cut grooves 3 is increased, when the blocks 4 are subjected to the braking force F, as shown in FIG. Since the opening of the block 4 in the cut groove 3 tends to close due to the collapse of the block 4, the expected edge effect cannot be obtained. If the number is increased too much, the rigidity of the blocks 4 will be reduced, which tends to lead to a decrease in the contact area of the tread surface.

Furthermore, when a rubber composition that does not become hard even at low temperatures is used as the tread rubber, the blocks 4 do not become hard when running on ice, making it easy for the blocks 4 to collapse, resulting in a reduction in the contact area of the tread surface. is unavoidable.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and provides a studless pneumatic radial system that further improves braking performance on icy roads. The purpose is to provide tires.

[0007]

[Means for Solving the Problems] The pneumatic radial tire of the present invention has a plurality of main grooves provided on the tread surface at least in the tire circumferential direction over one circumference of the tire, and a plurality of cut grooves connecting these main grooves. A rib or block pattern is formed by cutting in the width direction of the tire, and the cross-sectional shape of the cut groove in the tire circumferential direction is shaped like a funnel in which both groove walls protrude convexly, and the bottom of the groove in this funnel shape is formed. The groove width t of the tread surface is t=0.4 to 1.5 mm, and the groove width T of the tread surface is
is characterized in that T=2t to 6t.

[0008] In this way, in the present invention, since the cross-sectional shape of the cut grooves in the tire circumferential direction is funnel-shaped as described above, the thin blocks divided into these cut grooves respond to external forces in the tire circumferential direction in terms of material mechanics. Since it acts as a "equal-strength beam," it absorbs more energy than blocks that are simply divided by straight grooves, making it possible to reduce the collapse of the block when driving on ice.

Therefore, according to the present invention, even when a rubber composition that does not harden even at low temperatures is used as the tread rubber, or when the number of sub-grooves or cut grooves is increased, the contact area of the tread surface is reduced due to the collapse of the blocks. Since this does not cause the closure of the cut grooves, it is possible to improve the braking performance on ice. Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a plan view showing an example of the tread pattern of the pneumatic radial tire of the present invention. In FIG. 1, the tread surface M has four main grooves 10, 11, 12, and 13 extending around one circumference of the tire in the tire circumferential direction EE'.
are provided, and a plurality of sub grooves 20 connecting these main grooves are provided in the tire width direction from one shoulder portion 14 to the other shoulder portion 14, thereby forming a large number of blocks 30. m is the equator line, and W is the tread contact width.

All of the blocks 30 have two cut grooves 40 carved on their surfaces in the tire width direction from one end of the block 30 to the other, so that each block 30 has a plurality of sub-blocks 31. , 32, and 33
It is divided into. At least one cut groove 40 may be formed on the surface of the block 30. Furthermore, if a rib is formed on the tread surface M, the cut grooves 40 may also be carved into the rib.

In FIG. 1, the cut grooves 40 are provided in a direction substantially perpendicular to the tire circumferential direction EE', but the cut grooves 40 do not necessarily have to be perpendicular to the tire circumferential direction EE'.
It is possible to arrange it in the range of 45° to 90° with respect to E'. In the present invention, the cross-sectional shape of the cut groove 40 in the tire circumferential direction is formed into a funnel shape with both groove walls protruding from each other in a convex shape. FIG. 2 shows a cross section taken along line A-A in FIG. In FIG. 2, groove walls 40a and 40b of the cut groove 40 each protrude inward from the groove in a convex shape. That is, a straight line a-b indicated by a dotted line connecting the groove end a in the groove width direction of the groove bottom and the groove end b in the groove width direction of the groove opening end in contact with the surface of the block 30.
In contrast, both groove walls 40a and 40b protrude inward from the groove in a convex manner, and the cross section of the groove as a whole is formed into a funnel shape. Although it is desirable to form such a funnel shape in all the cut grooves 40, it may be formed in only some of the cut grooves 40. Preferably, cut grooves 40 around the entire circumference of the tire.
It is preferable that it is 50% or more of the total number of .

[0013] The cut groove 4 formed in a funnel shape in this way
For 0, when the groove width of the groove bottom is t and the groove width of the tread surface is T, t=0.4~1.5mm, T=2t~
The relationship 6t must be satisfied. If t is less than 0.4 mm, it will be difficult to form the cut grooves 40 in tire manufacturing, and if t is more than 1.5 mm, the contact area of the tread surface will be reduced. Further, if T is less than 2t, the effect of improving the rigidity of the block is small, and if T is more than 6t, the ground contact area of the tread surface decreases, resulting in a decrease in braking performance on ice.

In FIG. 2, there is no particular limit to the groove depth D, but a range of 60% to 95% of the main groove depth is usually appropriate. In order to obtain the above-mentioned funnel-shaped groove cross-sectional shape, the groove width T' at the groove depth position x preferably satisfies the following relationship.

[0015]

By determining the cross-sectional shape of the cut grooves 40 as described above, the thin blocks divided by the cut grooves 40 are given a function of "equal strength" and the absorbed energy of the thin blocks is increased. Therefore, even if braking force F is applied in the direction of the arrow as shown in FIG. 3 while driving on ice, it is possible to suppress the falling of the thin blocks and prevent a decrease in the ground contact area of the tread surface.

[0017]

[Example] The following three types of radial tires having the tread pattern shown in FIG. 1 and having a tire size of 165R138PRLT were manufactured. All other structures such as the carcass layer and belt layer and manufacturing conditions were the same for all tires. In addition, for any tire, the tread contact width W
: 133 mm, each groove width of main grooves 10, 11, 12 and 13: 6 mm, the groove depth: 11.6 mm,
Groove width of minor groove 20: 6.5 mm, groove depth of minor groove 20: 1
1.6 mm, number of minor grooves 20 around the entire tire circumference:
There were 52 pieces.

The braking performance on ice of these tires was evaluated by the following method. The results are shown in FIG. ■ Tire of the present invention. Groove width of the cut groove 40: 2.5 mm, groove depth of the cut groove 40: 8 mm. The cut grooves 40 are shown in the cross section in the tire circumferential direction as shown in FIG.
Form into a funnel shape as shown. t: 0.8mm.

[0019]

■ Conventional tire 1. Same as the tire of the present invention described above, except that the cut groove 40 is U-shaped with a groove width of 0.8 mm. ■ Conventional tire 2. Same as the tire of the present invention described above except that the cut groove 40 is U-shaped with a groove width of 2.5 mm.

[0021] Evaluation method of braking performance on ice: Using a friction tester under 0°C conditions, the test was carried out in a straight line on ice at a speed of 10 km/h under an air pressure of 4.5 kg/cm2 (tires did not rotate). ) Contact pressure when changing load (k
This was done by plotting the relationship between gf/cm2) and braking force (index) on a graph (FIG. 4).

In addition, in FIG. 4, the surface pressure 8. of the conventional tire 1 is shown.
The index evaluation is shown when the braking force at 0 kgf/cm2 is set as 100. In both cases, the larger the index value, the better the result. As is clear from the results in Figure 4, the tire of the present invention has a braking performance on ice of 25% compared to the conventional tire.
% has also improved.

[0023]

As explained above, according to the present invention, the cut grooves on the tread surface have a cross-sectional shape in the circumferential direction of the tire in a funnel shape in which both groove walls protrude convexly, and in this funnel shape. The groove width t of the groove bottom is t=0.4~1
．． 5 mm, and the groove width T on the surface is set to T=2t to 6t, making it possible to sufficiently improve the braking performance on ice.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a tread pattern of a pneumatic radial tire of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG. 1.

FIG. 3 is an explanatory cross-sectional view showing the state of the block during braking of the pneumatic radial tire of the present invention.

FIG. 4 is an explanatory diagram comparing the braking performance on ice of a pneumatic radial tire of the present invention and a conventional pneumatic radial tire.

FIG. 5 is an explanatory cross-sectional view showing the state of cut grooves in a block during braking of a conventional pneumatic radial tire.

FIG. 6 is an explanatory cross-sectional view showing the state of cut grooves in a block after braking of a conventional pneumatic radial tire.

FIG. 7 is an explanatory cross-sectional view showing the state of a block during braking of a conventional pneumatic radial tire.

FIG. 8 is an explanatory cross-sectional view showing the state of a block of a conventional pneumatic radial tire after braking.

[Explanation of symbols]

M tread surface 10, 11,
12, 13 Main groove 20 Minor groove 30 Block
40 Cut groove

Claims (1)

[Claims] [Claim 1] A plurality of main grooves are provided on the tread surface at least in the tire circumferential direction over one circumference of the tire, and a plurality of cut grooves connecting these main grooves are cut in the tire width direction to form a rib or block pattern. The cross-sectional shape of the cut groove in the tire circumferential direction is a funnel shape in which both groove walls protrude convexly, and the groove width t of the groove bottom in this funnel shape is set to t=0.4 to 1. A pneumatic radial tire with a groove width T of 2t to 6t on the tread surface.