GB2343159A

GB2343159A - Pneumatic tyre tread portion

Info

Publication number: GB2343159A
Application number: GB9924937A
Authority: GB
Inventors: Yukio Nakao; Tetsuya Sakuno
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1998-10-26
Filing date: 1999-10-22
Publication date: 2000-05-03
Anticipated expiration: 2019-10-22
Also published as: JP2000127715A; GB9924937D0; GB2343159B; JP3035277B1

Abstract

The tread portion (2) has groove sets alternating on each side of the tyre equator (CO), each set including a first main groove (9A) having an axially inner end (P1) closed at or near the tyre equator (CO) and an axially outer end (P2) and inclining towards one circumferential direction, a second main groove (9B) extending axially outwardly from a division-point (Q1) on the groove (9A) to a tread edge (Te), while inclining towards said one circumferential direction, a short blind groove (12) extending circumferentially and connected between its closed ends to the outer end of groove (9A) having a circumferential length (L1) from 2.0 to 3.5 times groove width (W1) of that end, the axial distance (L2) between the groove (12) and the adjacent tread edge (Te) being from 0.1 to 0.2 times the tread width. The groove (9A) is inclined at 13 to 18 degrees to the tyre equator extending in at least a tread centre region (Y) 25 % of the tread width (TW) and has greater inclination axially outwardly. The groove (9B) is inclined at 55 to 65 degrees to the tyre equator (CO).

Description

PNEUMATIC TYRE The present invention relates to a pneumatic tyre, more particularly to an improved tread pattern capable of improving dry grip performance and wet performance during running on paved roads at high speed.

In a pneumatic tyre used under very high speed conditions such as a high-performance tyre for circuit racing, a tread pattern (pl) shown in Fig. 8 is often used, wherein in order to improve wet performance such as resistance to aquaplaning phenomenon, V-shaped main grooves (a) extending from one tread edge (el) to the other tread edge (e2) are provided, and the inclination of the main grooves with respect to the tyre axial direction is decreased in the tread shoulder regions in order to increase lateral stiffness.

In this tread pattern (pl), good drainage is obtained. However it is difficult to further increase grip performance especially under dry conditions because the main grooves (a) circumferentially divide the tread rubber into blocks (B) and thus it is difficult to increase rigidity.

It is therefore, an object of the present invention to provide a pneumatic tyre, in which the tread rigidity can be greatly increased whilst maintaining good drainage to further improve wet and dry performances such as dry grip performance, resistance to aquaplaning and the like.

According to the present invention, a pneumatic tyre comprises a tread portion provided with no groove extending continuously in the tyre circumferential direction, characterised by plural groove sets disposed on alternating sides of the tyre equator, each of the groove sets including a first main groove, a second main groove and a short blind groove, said first main groove having an axially inner end closed near the tyre equator and an axially outer end, and extending axially outwardly from the inner end, while inclining towards one circumferential direction, said second main groove extending axially outwardly from a division-point on said first main groove to one tread edge, while inclining towards said one circumferential direction said short blind groove extending circumferentially of the tyre and having closed ends, the short blind groove having a circumferential length (H) being in the range of from 2.0 to 3.5 times the groove width of the first main groove in the axially outer end portion, the minimum axial distance between the short blind groove and the axially adjacent tread edge being in the range of from 0.1 to 0.2 times the tread width, the axially outer end of the first main groove being connected to the short blind groove at a point between said closed ends, the first main groove comprising an axially inner gently inclining portion and an axially outer steeply inclining portion, said axially inner gently inclining portion being inclined at an angle al of from 13 to 18 degrees with respect to the tyre equator, and extending in at least a tread centre region having a width of 25 % of the tread width, said second main grooves being inclined at an angle ss of from 55 to 65 degrees with respect to the tyre equator.

An embodiment of the present invention will now be described by way of example only in conjunction with the accompanying drawings, in which: Fig. 1 is a cross sectional view of an embodiment of a tyre of the present invention; Fig. 2 is a developed view showing an example of the tread pattern thereof; Fig. 3 (A) and 3 (B) are diagrams each showing a staggered groove arrangement; Figs. 4 to 7 are graphs showing test results; Fig. 8 shows a conventional tread pattern; and Fig. 9 shows a tread pattern used in comparison tests.

In Fig. l, a pneumatic tyre 1 according to the present invention comprises a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each with a bead core 5 therein, a carcass 6 extending between the bead portions 4, and a belt 7 disposed radially outside the carcass 6.

The tyre 1 in this embodiment is a low-aspect radial tyre for racing cars or sport cars. The tread portion 2 is provided with a unidirectional tread pattern.

The tread portion 2 is not provided with a circumferential groove extending continuously in the tyre circumferential direction, or an axial groove extending continuously from one of the tread edges to the other, wherein the circumferential groove and the axial groove have a groove width of more than 2.5 mm.

The tread portion 2 is provided on each side of the tyre centreline or equator CO with main grooves 9 each inclined at a certain angle with respect to the tyre circumferential direction. The main grooves have a width of more than 2.5 mm. There is no narrow groove (including slit or cut called sipe) having a width of less than 2.5 mm.

The main grooves 9 comprise first main grooves 9A and second main grooves 9B. Each of the first main grooves 9A has an axially inner end P1 near the tyre equator CO and an axially outer end P2 in the middle of a half tread width between the tyre equator CO and a tread edge Te, and extends axially outwardly from P1 to P2, while inclining towards one of the circumferential directions (in Fig. 2 upwards). The relation between this inclining direction and the intended direction of tyre rotation in the unidirectional pattern is such that the axially inner end P1 comes into contact with the ground prior to the axially outer end P2 when the tyre is used on a vehicle.

The axially inner ends P1 of the first main grooves 9A are staggered around the tyre equator CO.

Preferably, the axially innermost point of each inner end Pl contacts the tyre equator CO as shown in Fig. 2. It is also possible to leave space therebetween as shown in Fig. 3 (A) wherein the axial distance K1 between the axially inner ends P1 is set in the range of less than 0.1 times the tread width TW. Further, it may be possible that the first main grooves 9A extend slightly beyond the tyre equator CO as shown in Fig. 3 (B) wherein the maximum axial overlap K2 is set in the range of less than 0.1 times the tread width TW. Here, the tread width TW is the maximum axial width of the ground contacting area measured under a standard condition in which the tyre is mounted on a standard rim and inflated to a normal pressure and then loaded with a normal load.

The first main groove 9A is composed of a gently inclining portion 10 which is defined as inclining at an angle al of from 13 to 18 degrees, preferably 14 to 16 degrees with respect to the tyre circumferential direction, i. e. the tyre equator, and a steeply inclining portion 11 which is defined as inclining at an angle a2 being larger than the angle al and increasing towards the outer end P2.

The gently inclining portion 10 extends axially outwardly from the inner end P1 in at least a tread centre region Y having a width W of 0.25 times the tread width TW.

The steeply inclining portion 11 extends from the axially outer end of the gently inclining portion 10 to the outer end P2.

At the outer end P2, the steeply inclining portion 11 is connected to the middle of a short blind groove 12.

The blind groove 12 extends in the tyre circumferential direction, and both the circumferential ends are closed.

The circumferential length LI between the closed ends is set in the range of from 2.0 to 3.5 times the groove width W1 of the gently inclining portion 10 measured in the axially outer end portion. The width W2 of the blind groove 12 is less than the groove width W1, usually in the range of from 0.5 to 0.7 times W1. The axial distance L2 between the blind groove 12 and the tread edge Te is set in the range of from 0.1 to 0.2 times the tread width TW.

If the length Ll is less than 2.5 times W1 and/or the length L2 is more than 0.2 times TW, it is difficult to improve wet performance. If the length LI is more than 3.5 times W1 and/or the length L2 is less than 0.1 times TW, it is difficult to maintain the rigidity of the tread shoulder region.

Each of the second main grooves 9B extends axially outwardly from a division-point Q1 in the gently inclining portion 10 of one of the first main grooves 9A to the tread edge Te, while inclining towards the same circumferential direction as in the first main groove 9A. Thus, the second main groove 9B opens to the tread edge Te at the axially outer end Q2. The inclination angle ss of the second main grooves 9B is in the range of from 55 to 65 degrees with respect to the tyre circumferential direction.

In Fig. 2, the second main grooves 9B are straight.

However, it is also possible to curve the second main grooves 9B by gradually increasing the inclination angle a towards the outer open end Q2.

Preferably, the major part 11A of the abovementioned steeply inclining portion 11 is substantially parallel to the second main groove 9B to the intersection with the blind groove 12. The above-mentioned inclination angles al, a 2 and are defined as of the groove centre line with respect to the circumferential direction of the tyre.

Therefore, in the tread portion 2, a plurality of independent groove-sets, each made up of a first main groove 9A, a second main groove 9B and a short blind groove 12, are formed in a staggered arrangement around the tyre equator CO.

Fig. 4 shows results of comparison tests between a staggered arrangement Tl and a V-formation T2 of main grooves, wherein the main grooves are simplifie as linear grooves. From the test, it was confirmed that the staggered arrangement T1 improved the dry grip performance and wear resistance while maintaining the wet performance at the same level as the V-formation T2.

Fig. 5 shows results of confirmation tests, wherein the inclination angle al in the staggered arrangement T1 shown in Fig. 4 was changed.

Fig. 6 shows results of comparison tests among three tread patterns T3, T4 and T5. In pattern T5, blind grooves 12 are provided. In the pattern T4, the blind grooves 12 are omitted. In pattern T3, the blind grooves 12 are omitted and the main grooves are extended to the tread edges Te. Owing to the blind grooves 12, a good wet performance at the same level as the pattern T3 can be obtained while maintaining a good dry grip performance and a good wear resistance at the same level as the pattern T4.

Fig. 7 shows results of confirmation tests, wherein the inclination angle ss of the second main grooves 9B in a tread pattern T6 shown therein were changed.

When the inclination angle ss was more than 65 degrees the wet performance decreased. When the inclination angle is less than 55 degrees, the dry grip performance decreases. Preferably, the inclination angle is set in the range of from 58 to 62 degrees.

In the wet performance test and dry grip performance test, a sport car provided on all the four wheels with test tyres (size 195/55R15) was run on a wet test circuit course and a dry test circuit course to measure lap time. And the measured lap time was evaluated into five ranks. In the wear resistance test, tread wear was evaluated into five ranks after the dry grip performance test. The evaluated results are plotted on the graphs as Performance Index. The higher the value, the better the performance.

Table 1 shows results of comparison tests between the tread shown in Fig. 2 and a tread shown in Fig. 9.

Table 1

Tyre Ex. 1 Ref. 1 Tread pattern *1 Fig. 2 Fig. 9 Groove width W1 10 10 (mm) First main groove Inclination al 15 deg.- Distance LI 0.125 TW Kl or K2 (mm) 0 Second main groove Inclination 60 deg.

Blind groove Length LI 3.0 W1-- Groove width W2 0.6 Wl Wet performance Lap time 1'03"2 1'04"5 Performance index 5 4 Dry grip performance Lap time 57"7 58"1 Performance index 5 4.5 Wear resistance 4 3. 5 *1) Negative ratio in the ground contacting patch was 25%.

The present invention can be suitably applied to a high-performance circuit-racing tyre, but it is also possible to apply to a passenger tyre and the like.

Claims

CLAIMS 1. A pneumatic tyre comprising a tread portion (2) provided with no groove extending continuously in the tyre circumferential direction, characterised by plural groove sets disposed on alternating sides of the tyre equator (CO), each of the groove sets including a first main groove (A), a second main groove (9B) and a short blind groove (12), said first main groove (9A) having an axially inner end (P1) closed near the tyre equator (CO) and an axially outer end (P2), and extending axially outwardly from the inner end, while inclining towards one circumferential direction (CO), said second main groove (9B) extending axially outwardly from a division-point (Q1) on said first main groove (9A) to one tread edge (Te), while inclining towards said one circumferential direction (CO) said short blind groove (12) extending circumferentially of the tyre and having closed ends, the short blind groove (12) having a circumferential length (H) being in the range of from 2.0 to 3.5 times the groove width (WH) of the first main groove (9A) in the axially outer end portion, the minimum axial distance (L2) between the short blind groove (12) and the axially adjacent tread edge (Te) being in the range of from 0.1 to 0.2 times the tread width, the axially outer end of the first main groove (9A) being connected to the short blind groove (12) at a point between said closed ends, the first main groove (9A) comprising an axially inner gently inclining portion (10) and an axially outer steeply inclining portion (11), said axially inner gently inclining portion (10) being inclined at an angle al of from 13 to 18 degrees with respect to the tyre equator, and extending in at least a tread centre region (Y) having a width of 25 % of the tread width (TW), said second main grooves (9B) being inclined at an angle ss of from 55 to 65 degrees with respect to the tyre equator (CO).
2. A pneumatic tyre according to claim 1, characterised in that said division-point (Q1) is located in the gently inclining portion (10).
3. A pneumatic tyre according to claim 1 or 2, characterised in that the axially inner gently inclining portion (10). is straight, the second main groove (9B) is straight, the blind-groove (12) is straight and parallel to the tyre equator (CO), and the axially outer steeply inclining portion intersects the blind-groove (12) at substantially the same angle as the inclination angle ss of the second main groove (9B).

3. A pneumatic tyre according to claim 1 or 2, characterised in that the axially inner gently inclining portion (10) is straight, the second main groove (9B) is straight, the blind-groove (12) is straight and parallel to the tyre equator (CO), and the axially outer steeply inclining portion intersects the blind-groove (12) at substantially the same angle as the inclination angle P of the second main groove (9B).

Amendments to the claims have been filed as follows 1. A pneumatic tyre comprising a tread portion (2) provided with no groove extending continuously in the tyre circumferential direction, characterised by plural groove sets disposed on alternating sides of the tyre equator (CO), each of the groove sets including a first main groove (A), a second main groove (9B) and a short blind groove (12), said first main groove (9A) having an axially inner end (PI) closed nutually at the tyre equator (CO) and an axially outer end (P2), and extending axially outwardly from the inner end, while inclining towards one circumferential direction (CO), said second main groove (9B) extending axially outwardly from a division-point (Q1) on said first main groove (9A) to one read edge (Te), while inclining towards said one circumferential direction (CO) said short blind groove (12) extending circumferentially of the tyre and having closed ends, the short blind groove (12) having a circumferential length (H) being in the range of from 2.0 to 3. 5 times the groove width (WH) of the first main groove (9A) in the axially outer end portion, the axial distance (L2) between the short blind groove (12) and the axially adjacent tread edge (Te) being in the range of from 0.1 to 0.2 times the tread width, the axially outer end of the first main groove (9A) being connected to the short blind groove (12) at a point between said closed ends, the first main groove (9A) comprising an axially inner inclined portion (10) and an axially more steeply inclined portion (11), said axially inner gently inclining portion (10) being inclined at an angle al of from 13 to 18 degrees with respect to the tyre equator, and extending in at least a tread centre region (Y) having a width of 25 % of the tread width (TW), said second main groove (9B) oeing inclined at an angle P of from 55 to 65 degrees with respect to the tyre equator (CO).

2. A pneumatic tyre according to claim 1, characterised in that said division-point (Q1) is located in the gently inclining portion (10).