JPH04212604A - Pneumatic tire for icy road - Google Patents

Abstract

PURPOSE:To offer such an icy-snowy peumatic tire that is made so as to improve the extent of snowy maneuverability without entailing any drop in that of icy maneuverability by reconciling both the snowy and icy maneuverabilities in relation of being contrary to each other. CONSTITUTION:In a pneumatic tire with a block pattern which is a groove area ratio of a tread pattern is 20-50%, and the value of a snow traction index STI being determined by STI=-6.8+2202pg+672ps+7.6Dg [where, rhog: (whole groove length projected in the tire width direction)/(ground width X peripehral length)/(1/mm), rhos:(the whole sipe length projected in the tire width direction)/(ground width X peripheral length)(1/mm). Dg: means groove depth (mm) is a range of 170-240, it is a icy-snowy pneumatic tire provided with a block row, setting W1 and W2 different in size that a block interval in the tire circumferential direction is set by a following equation, more than at least two rows. W1=PXL/N, W2=(2-P)XL/N, 1.2<=P<1.7, where P is an optional number, L is total length of the block interval in the tire circumferential direction and N is the total number of the block in the tire circumfernetial direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire for use on icy roads that has improved performance on fresh snow without reducing performance on ice.

0002

2. Description of the Related Art In recent years, studless tires have been in the spotlight as tires for icy and snowy roads in place of spiked tires. This studless tire is based on a block pattern in which blocks are arranged at approximately equal intervals in the tire circumferential direction, and each block has a plurality of approximately parallel sipes, and the groove area in the tire width direction is 20 to 50%. DeSA
Generally, the STI value defined by Epaper 820345 is 170 to 240.

[0003] However, with the spread of such studless tires, it is desired to improve the driving performance (driving performance and braking performance) on fresh snow. In order to improve driving performance on snowy roads, it is effective to increase the block spacing in the tire circumferential direction, but this increases the groove area ratio, which in turn reduces driving performance on icy roads. There is a problem with it.

0004

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and it harmonizes on-snow performance and on-ice performance, which have a contradictory relationship with each other, without reducing on-ice performance. An object of the present invention is to provide a pneumatic tire for use on icy and snowy roads, which improves performance on snow.

[0005]

[Means for Solving the Problems] The present invention provides a snow traction index formula STI=-6.8+2202ρg+6 in which the groove area ratio of the tread pattern is 20 to 50%.
72 ρs+7.6Dg [However, ρg: (total groove length projected in the tire width direction)/(ground contact width x circumference) (1/
mm), Dg: Average groove depth (mm)] The value of the snow traction index STI is 17.
In a pneumatic tire having a block pattern of 0 to 240, at least two rows of blocks are provided in which block intervals in the tire circumferential direction are alternately arranged in the circumferential direction with different sizes W1 and W2 whose block intervals are determined by the following formula. Pneumatic tires for icy and snowy roads.

[0006]

[0007] Here, P is an arbitrary number, L is the total length of block intervals in the tire circumferential direction, and N is the total number of blocks in the tire circumferential direction. By arranging the wide block intervals W1 alternately in the tire circumferential direction, the snow column shearing effect is improved,
Improves performance in fresh snow. Moreover, the groove area ratio and S
TI maintains the standard of conventional studless tires, so there is no reduction in performance on ice.

Hereinafter, the means of the present invention will be explained in detail with reference to the drawings. FIG. 1 shows an example of the tread pattern of the pneumatic tire for icy and snowy roads according to the present invention. In the figure, a tread 1 has a block pattern consisting of a plurality of blocks 4 partitioned by a plurality of main grooves 2 provided along the tire circumferential direction E-E and a plurality of sub-grooves 3 provided in the tire width direction. is formed. In the illustrated example, four block rows are formed, and a plurality of sipes 5 are arranged in the blocks 4 of each block row along the tire width direction. In such a block pattern, the groove area ratio is set in the range of 20 to 50% and the STI is set in the range of 170 to 240, which are the same as in conventional tires. Here, the groove area ratio is the ratio of the groove area to the total ground contact area of the tread surface. Also, Snow Traction Index (STI) is SAE Paper 8203
This is an index indicating the on-snow performance level calculated from the tire cross-sectional direction (tire width direction) component of the length of the grooves and sipes on the tread pattern surface described in No. 45 and the groove depth.

[0009] The interval between the blocks 4 arranged in the tire circumferential direction in each block row (width of the sub-groove 3) is such that W1 and W2 of different sizes are arranged alternately, and W1 and W2 are set within a range determined by the following formula.

0010

In these equations, L is the total block interval in the tire circumferential direction per block row, N is the total number of blocks in the tire circumferential direction per block row, and P is 1.2.
It is an arbitrary number determined within the range of ~1.7, and may be set for each tire. As mentioned above, this arbitrary number P must be in the range of 1.2≦P<1.7, and if P is 1.7 or more, the rigidity of the end of the block that makes up the groove width W1 will decrease. However, the edge effect at the end of the block is reduced. Furthermore, if P is smaller than 1.2, the present invention cannot expect to improve the snow column shearing force. This arbitrary number P is
More preferably, 1.3≦P≦1.5.

FIG. 2 shows another embodiment of the invention. In the embodiment shown in FIG. 1, all the block rows are arranged so that the block spacing is alternately large width W1 and small width W2, but in this FIG. and W2, and the block rows in the shoulder area on both the left and right sides have the same block interval.

According to the above-described tire of the present invention, by alternately arranging large widths W1 in the intervals between the blocks in the tire circumferential direction, the shearing force of the snow column formed between the blocks is increased, and the performance on snow is improved. . In addition, by setting the groove area ratio and STI to the same level as conventional studless tires, a significant decrease in on-ice performance can be prevented.

[0014]

[Example] Tire size is 185/70 R13 8
5Q are all the same and have the block pattern shown in Figure 1, the groove area ratio is 40%, the groove depth is 10 mm, the snow traction index (STI) is 200, and the L (
The total block interval in the tire circumferential direction) is 500 mm,
Keep N (the total number of blocks in the circumferential direction of the tire) constant at 50, and set only the arbitrary number P to 1.0, 1.2, 1.5,
1.7, four types of pneumatic tires A, B, C, and D for ice and snow roads were prototyped. Also, the block pattern shown in FIG. 2 is used, the groove area ratio, STI, L, and N are the same as in the above case, and the center two block rows have P set to 1.
5. A pneumatic tire F for icy and snowy roads was manufactured as a prototype in which the two block rows on the left and right had P of 1.0. Of these, tires B and C
, F correspond to the present invention, and tire A corresponds to the conventional tire.

[0015] Tires having these five types of tread patterns were each equipped with an air pressure of 1.9 kgf/cm2 and a rim of 1.
It has a 1800CC engine as a 3×5 1/2JJ and is installed in a FF car (front engine front wheel drive), with an average slope of 7.
The average speed when passing through a 200 m section on a freshly snowed road of 20° was measured, and the performance on snow was evaluated. The results were as shown in Figure 3. The performance on snow was expressed as an index when the measured value of Tire A was set as 100.

[0016] In addition, the vehicle ran on an ice floe at an initial speed of 40 km/h and measured the braking distance when braking to evaluate the performance on ice. The results were as shown in FIG. The performance on ice was expressed as the reciprocal of the braking distance as an index with Tire A as 100. As can be seen from the table, tires B, C, and F of the present invention have improved on-snow performance while maintaining braking performance on ice at the same level as conventional tire A. Furthermore, it can be seen that Tire D with P<1.7 significantly improves the performance on snow, but the performance on ice significantly decreases.

[0017]

As described above, according to the present invention, the groove area of the block pattern and the snow traction index (STI) are set at the level of conventional studless tires, and the groove width W1 is large as the block interval in the block row.
Since these are arranged alternately, it is possible to improve the performance on the snow without reducing the performance on the ice.

[Brief explanation of the drawing]

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

FIG. 2 is a plan view showing an example of a tread pattern constituting the tread surface of the pneumatic radial tire of the present invention.

FIG. 3 is a comparison diagram of on-snow performance.

FIG. 4 is a comparison diagram of the on-ice performance of the tires.

[Explanation of symbols]

1 Tread pattern 2 Main groove 3 Minor groove 4 Block 5 Sipe

Claims (1)

[Claims] [Claim 1] The groove area ratio of the tread pattern is 20.
~50%, STI=-6.8+2202ρg+672
ρs+7.6Dg [however, ρg: (total groove length projected in the tire width direction)/(ground contact width x circumference) (1/mm
), ρs: (total sipe length projected in the tire width direction)/(contact width x circumference) (1/mm), Dg: average groove depth (mm)] The value of the snow traction index STI is In a pneumatic tire having a block pattern of 170 to 240 mm, at least two or more block rows are provided in which block intervals in the tire circumferential direction are alternately arranged in the circumferential direction with different sizes W1 and W2 determined by the following formula. Pneumatic tires for icy and snowy roads. However, P is an arbitrary number, L is the total block interval in the tire circumferential direction, and N is the total number of blocks in the tire circumferential direction.