CA2018565A1

CA2018565A1 - Heavy duty pneumatic tire

Info

Publication number: CA2018565A1
Application number: CA002018565A
Authority: CA
Inventors: Tetsuhito Tsukagoshi
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1989-06-09
Filing date: 1990-06-08
Publication date: 1990-12-09
Also published as: JPH0310910A; DE4018463A1

Abstract

HEAVY DUTY PNEUMATIC TIRE
Abstract of the Disclosure A heavy duty pneumatic tire is for use in a vehicle such as a truck, bus and the like. The tire includes two pairs of narrow grooves spaced in a width direction and extending in a circumferential direction and a plurality of sipes formed between two narrow grooves positioned on an inner side of the width direction with a constant interval in the circumferential direction. Dimensions of the narrow grooves and the sipes fulfill the following relations.
C = (0.10-0.30) x T
W = (0.03-0.14) x T
K = (0.05-0.50) x A, where T is a width of a tread of the tire, C is a distance from a tread edge to the narrow groove positioned on an outer side, W is a distance between each pair of the narrow grooves, A is a distance between the narrow grooves positioned on the inner side, and K
is a distance between the sipes in the circumferential direction.

Description

`` 2018~6~

HEAVY DUTY P~EUUATIC TIRE

This invention relates to a heavy duty pneumatic tire applicable to trucks, buses and the like, and more particularly to a pneumatic tire whose wear-resistance is improved without detrimentally affecting wet 05 performance, or performance on wet roads.
With heavy duty pneumatic tires for use in heavy vehicles such as trucks, buses and the like, there has developed recently great requirement for wear-resistan~e, particularly irregular wear-resistance which is a performance for wear called as railway wear or river wear. A tire having a tread pattern shown in Fig. 1 is one of proposals to fulfill such a requirement.
In the tire 10 shown in Fig. 1, a tread 12 is formed with a plurality of circumferential main grooves 14 spaced apart from each other and extending in a circumferential direction of the tire, pairs of narrow grooves 16 formed in ends of the tread 12, respectively, and extending in the circumferential direction, and sipes 18 formed in shoulders and extending in a radial direction of the tire. A radial length of rib 20 defined by each pair of narrow grooves 16 is made shorter than a radial length of ribs 22 and 24 adjacent `` 201856~
the rib 20 to cause forces in braking directions of the tire or negative shearing forces in the ribs 20, thereby effectively preventing irregular wear from occurring in the ribs 22 and 24.
With such a tire 10, however, although the irregular wear is effectively prevented by forming the narrow grooves 16 in the tread 12 of the tire 10, sufficient drainage could not be ensured because of the narrow width of the narrow grooves 16. Therefore, this tire 10 is inferior in steering stability on wet roads to a tire 10' having circumferential main grooves 14 as shown in Fig. 2. Such a problem of the tire 10 has not yet been solved sufficiently irrespective of various efforts.
1~ On the other hand, although the tire 10' shown in Fig. 2 is superior in drainage, the tire 10' is likely to suffer irregular wear.
It is an object of the invention to provide a heavy duty pneumatic tire improved in wear-resistance without detrimentally affecting steering stability on wet roads.
In order to accomplish this object, a heavy duty pneumatic tire for a vehicle such as a truck, bus and the like according to the invention comprises two pairs of narrow grooves spaced in a width direction and extending in a circumferential direction and a plurality 201856~
of sipes formed between two narrow grooves positioned on an inner side of the width direction with a constant interval in the circumferential direction, and dimensions of the narrow grooves and the sipes fulfilling the following relations, C = (0.10-0.30) x T
W = (0.03-0.14) x T
K = (0.05-0.50) x A, where T is a width of a tread of the tire, C is a distance from a tread end to the narrow groove positioned on an outer side, W is a distance between each pair of the narrow grooves, A is a distance between the narrow grooves positioned on the inner side, and K
is a distance between the sipes in the circumferential 1~ direction.
The tire according to the invention can effectively prevent irregular wear on ribs except narrow ribs defined by the two pairs of the narrow grooves and effect drainage along the sipes formed in zones defined by the two pairs of the narrow grooves, while maintaining the draining performance along circumferential directions of the tire.
According to the invention, the narrow grooves positioned on the outer side of the width direction are located at the distance C = (0.10-0.30) x T from the tread ends, where T is the tread width. If the C is ``` 201856~
less than 0.10 x T, the rigidity of ribs from the tread ends is too low so that negative shearing forces are ineffective. On the other hand, if the C is more than 0.30 x T, the narrow grooves are positioned too near the center of the tire so that the effect of preventing irregular wear at shoulders will decrease.
The reason why the narrow grooves are formed in pairs is as follows. Relatively large negative shearing force components are caused in the ribs formed between the narrow grooves, while shearing forces occurring in the other ribs except the ribs defined by the pairs of the narrow grooves are effectively shifted into positive directions, thereby preventing occurrence and development of cores causing irregular wear occurring 1~ along edges of the other ribs resulting f rom drag of tread rubber forming the ribs.
The reason why the distance W between the narrow grooves is (0.03-0.14) x T is that if the W is less than 0.03 x T, the negative shearing forces caused in the ribs defined between the pairs of the narrow grooves are insufficient so that negative shearing forces are also caused in the other ribs, with the result that the other ribs are also dragged and hence occurrence and development of cores of irregular wear in the other ribs cannot be effectively prevented.
On the other hand, if the W is more than `` 20~ 8~
0.14 x T, the negative shearing forces caused in the ribs defined by the pairs of the narrow grooves become too large so that the other ribs are affected by the large shearing forces to promote occurrence and 0~ development of cores of irregular wear.
In the zone between the narrow grooves positioned on the inner side of the width direction, sipes are formed spaced apart in the circumferential direction and the distance K between the adjacent sipes in the circumferential direction is (0.05-0.50) x A, where A is the distance between the narrow grooves positioned on the inner side.
With the distance X thus determined, the drainage through the sipes is ensured and so-called edge 16 effect and increase of contacting area with a road are accomplished. The edge effect means to cut water films formed on a road by edges of plural rubber blocks defined by the sipes. If the K is less than 0.05 x A, the requisite draining performance is maintained, but the rigidity of rubber blocks defined by the adjacent sipes becomes too low, with the result that the steering stability on a dried road is lowered and so-called polygonal wear is likely to occur in cornering. On the other hand, if the K is more than 0.5 x A, the rigidity of the rubber blocks defined by the ad~acent sipes becomes too high, with the result that contacting area 20~8~6~
with a road decreases and the steering stability on a wet road lowers.
The zone between the narrow grooves positioned on the inner sides of the width direction may of course 0~ be formed with one or more circumferential main grooves extending in the circumferential direction, if required, The drainage is more improved with this arrangement.
In order that the invention may be more clearly understood, preferred embodiments will be described, by way of example, with reference to the accompanying drawings.
Figs. la and lb and 2 illustrate tread patterns of the prior art;
Figs. 3a and 3b illustrate a preferred 1~ embodiment of the tire according to the invention;
Figs. 4a and 4b illustrate another preferred embodiment of the tire according to the invention;
Figs. 5a and 5b illustrate a further preferred embodiment of the tire according to the invention; and Fig. 6 is a view illustrating relations between running distances and widths of irregular wear with tires according to the invention shown in Figs. 3a, 4a and 5b and tires of the prior art.
Fig. 3a illustrates part of a tread pattern of a pneumatic tire according to the invention. As the inner construction of the tire is a general radial 20:l856~
construction, it will not be described in further detail.
The tread 12 is formed with two circumferential grooves 14 spaced apart from each other and extending in a circumferential direction in a center portionl and two pairs of narrow grooves 16a and 16b formed in ribs defined by the circumferential grooves 14 and tread edges, respectively. As a result of these grooves, there are formed ribs 32 between the circumferential grooves 14, and ribs 34 between the circumferential grooves 14 and the narrow grooves 16a. Moreover, sipes 36 are formed in the ribs 32 and the ribs 34, which are spaced in circumferential directions with a constant interval K.
1~ Each of the narrow grooves 16b positioned on an outer side of a width direction and extending in the circumferential direction is so formed that a distance C
from the tread end to an inner wall of the narrow groove 16b on an outer side of the width direction is within a range fulfilling a relation (0.10-0.30) x T. The T is a width of the tire tread 12.
Moreover, a distance W between each pair of the narrow grooves 16a and 16b or a distance between adjacent inner walls of each pair of the narrow grooves 16a and 16b is within a range fulfilling a relation (0.03-0.14) x T.

2~18~6~
It should be noticed in this case that a width of the narrow grooves 16a and 16b depends upon a depth h of the narrow grooves, but should fulfill a relation d = (0.05-0.3) x h, preferably d = (0.1-0.2) x h, when o~ h = 0.072 x T.
The reason why the narrow grooves are formed to fulfill the above relations is that when the tire contacts a ground, the opposed inner walls of each of the narrow grooves are brought into contact with each other so that movements of the tread rubbers at edges of the ribs defined by these narrow grooves are restrained, thereby effectively preventing occurrence and development of cores of irregular wear at the edges of the ribs.
1~ Moreover, as can be seen from Fig. 3b illustrating a section of the tread taken along the line ~b-~b in Fig. 3a, outer surfaces of the ribs 20 formed between the narrow grooves 16a and 16b are radially inward of surfaces of the ribs 32 and 34 and the ribs 35 defined by the narrow grooves 16b and the tread edges.
As a result, although the ribs 20 defined between the narrow grooves abut against a road surface similarly to the other ribs when the tread contacts the road surface, the ribs 20 on a side leaving the road surface are subjected to a large negative shearing forces so that drag at edges of the other ribs is prevented to 201856~
effectively prevent irregular wear of the tire.
As above described, ribs 32 bet~een the two circumferential main grooves 14 and ribs 34 between the main grooves 14 and the narrow grooves 16a are formed with sipes 36 oblique to an equatorial plane of the tire. Such sipes 36 are so formed to fulfill a relation K = (0.05-0.50) x A, where A is a distance between the narrow grooves 16a on the inner side of the width direction, and K is a distance between the sipes 36 in the circumferential direction. By forming the sipes 36 in the ribs 32 and 34, rigidities of tread rubbers in the respective ribs become proper values.
A depth t of the sipes 36 should be determined to fulfill a relation t = (0.6-1.0) x h and equal to or 1~ shallower than the depth of the circumferential main grooves 14, where h is the depth of the narrow grooves.
Moreover, an angle 0 of the sipes 36 made with the equatorial plane of the tire is freely selected within 0=0-90. In other words, the sipes 36 may extend in directions between in parallel with the equatorial plane and substantially at right angles to the equatorial plane.
Although the circumferential main grooves 14 are two in this embodiment, the number of the grooves is not limited to two. ~hey may be one or more than three in consideration of drainage performance of the tire.

Figs. 4a and 4b illustrate another embodiment of the tire according to the invention. In this embodiment, a rib 32 defined by narrow grooves 16a on an inner side of a width direction i5 not formed with o~ circumferential main grooves, but is formed with sipes 36 oblique relative to an equatorial plane of the tire and spaced with a constant interval in a circumferential direction of the tire. As can be seen from Fig. 4b illustrating a section of the tire along one sipe, the tire is substantially similar to the tire shown in Figs. 3a and 3b in the distance C between the tread end and the narrow groove 16b positioned on the outer side of the width direction, the distance W between the pair of narrow grooves 16a and 16b, and the intervals K in 1~ circumferential directions between the adjacent sipes, with exception of protrusions 38 spaced from each other in the extending directions of the sipes. Therefore, these similar features will not be explained for the sake of simplicity.
In this embodiment, the two protrusions 38 are provided spaced in the extending direction of the sipes 36. One or more than three protrusions may be formed dependently upon lengths of the sipes or angles ~ of the sipes made with the equatorial plane of the tire.
By changing the number of the protrusions 38, the rigidity of blocks defined by the adjacent sipes 36 and 201856~

the narrow grooves 16a can be freely changed.
The tire of this embodiment is somewhat inferior in wet performance to the tire shown in Figs. 3a and 3b in as much as the tire of this embodiment does not have the circumferential main grooves. ~owever, it is possible to mitigate occurrence of cores of wear at edges of the rubber blocks along the circumferential main grooves to improve the wear-resistance of the tire.
Figs. 5a and 5b illustrate a further embodiment of the tire according to the invention. Although it has circumferential main grooves 14 similar to those of the tire shown in Figs. 3a and 3b, it has particular sipes 36 which are formed in ribs 32 and 34 defined by circumferential main grooves 14 and narrow grooves 16a 1~ positioned on an inner side of a width direction.
The extending directions of the sipes 36 are changed with the respective ribs so as to be substantially in symmetry with respect to the circumferential main grooves 14 associated therewith. In order to improve the drainage of the tire by the sipes, widths of the sipes formed in the ribs 34 are uniformly widened from intermediate portions of the sipes to outer ends opening in the narrow grooves 16a, and depths of the widened portions of the sipes are narrower than those of the sipes according to this embodiment.
In this embodiment, the sipes 36 formed in the 2018~6~

ribs is formed with protrusions 38 spaced in extending directions of the sipes 36 to improve the rigidity of the rubber blocks defined by the sipes 36, the circumferential main grooves 14 and the narrow grooves 16a on the inner side of the width direction in the same manner as the embodiment shown in Figs. 4a and ~b.
The tire of this embodiment exhibits the good drainage performance and sufficient wear-resistance as in the embodiment shown in Figs. 3a and 3b. Moreover, abutment of the surface of the tire against a road surface is insured with the aid of the edge effect of the edges of the rubber blocks so that the wet performance and steering stability of the tire are improved.
1~ Although the sipes 36 formed in the rib 32 defined by the two circumferential main grooves 14 have uniform widths along the extending directions of the sipes 32, the widths of the sipes may be modified in following manner. For example, widths of the sipes are widened from intermediate portions of the sipes to ends opening in the circumferential main grooves, or widths of the sipes formed in the ribs 32 and 34 are substantially e~ual. Moreover, the ribs 32 and 34 defined by the circumferential main grooves 14 and the narrow grooves 16a positioned on the inner side of the width direction are formed in edges with further sipes 201~6~

extending in the width direction and spaced in the circumferential direction with a constant interval.
Test on the wet performance and wear-resistance was carried out with the tires according to the invention and tires of the prior art, which will be explained hereinafter.
Tires for the test Tires were used which had the general radial construction and whose sizes were lOOOR/20.
1~ Tire 1 according to the invention (Invention tire 1) The tires 1 used for the test had the pattern shown in Fig. 3 and had dimensions, the tread width T of 210 mm, distance C of 25 mm from the tread end to the narrow grooves positioned on the outer side of the width 1~ direction, distance W of 15 mm between each pair of narrow grooves, depth h of 15 mm of the narrow grooves, distance A of 120 mm between the narrow grooves positioned on the inner side of the width direction, and hence width d of 2.5 mm of the narrow grooves, distance K of 10 mm between the adjacent sipes in the circumferential direction, depth t of 13.5 mm of the sipes, width of 14 mm and depth of 15 mm of the circumferential main grooves.
Tires 2 according to the invention (Invention tire 2) The tires 2 had the tread pattern shown in Fig. 4a. The tires 2 had dimensions, the width T of 2 ~ 6 ~

210 mm of the tread, distance C of 24 mm between the end of the tread and the narrow groove positioned on the outer side of the width direction, distance W of 25 mm between the each pair of narrow grooves, depth h of 14 mm of the narrow grooves, distance A of 100 mm between the narrow grooves positioned on the inner side of the width direction or width d of 3 mm of the narrow grooves, distance K of 30 mm between the adjacent sipes, and depth t of 12 mm of the sipes.
Tires 3 according to the invention (Invention tire 3) The tires 3 had the tread pattern shown in Fig. 5a. The tire 3 had dimensions, the tread width T
of 215 mm, distance C of 34 mm between tread end and narrow grooves positioned on the outer side of the width 1~ direction, distance W of 12 mm between each pair of narrow grooves, depth h of 14 mm of the narrow grooves, distance A of 110 mm between the narrow grooves positioned on the inner side of the width direction or width d of 32.5 mm of the narrow grooves, distance K of ao 25 mm between the adjacent sipes in the circumferential direction, depth t of 14 mm of the sipes, width of 12 mm of circumferential main grooves, and depth of 14.5 mm of the circumferential main grooves.
Comparative example tire 1 The comparative example tire 1 had the tread pattern shown in Fig. la and had dimensions, the tread 2018~6~
width T of 215 mm, distance of 42 mm from the tread ends to centers of zigzags of narrow grooves positioned on the outer side of the width direction, distance of 9 mm between each pair of narrow groovesr depth of 15.2 mm of 0~ the narrow grooves, distance of 16.5 mm between circumferential main grooves, depth of 15.2 mm of the main grooves, and distance of 50 mm between centers of zigzags of the circumferential main grooves.
Comparative example tire 2 The comparative example tire 2 had the tread pattern shown in Fig. 2 and had dimensions, the tread width T of 205 mm, distance of 13.5 mm between the circumferential main grooves, depth of 15.2 mm of the main grooves, and distance of 40.5 mm between centers of 1~ zigzags of the circumferential main grooves.
Method of testing The tires above described were filled with normal pressure and alternately eguipped on a vehicle.
The vehicle equipped with the tires was driven under 110% normal load on a road with water films of 1.2 mm at 40 km/h, 60 km/h and 80 km/h, respectively. Wet limit performance was measured by feeling and estimated by indexes. In this case, the higher the index, the performance is higher.
Wear resistance The tires filled with the normal inner pressure 201~6~
were equipped on the vehicle. The vehicle equipped with the tires was driven under the normal load. After running 60,000 km, widths of irregular wears occurred were measured.
Result of the test Result of wet performance test is shown in the following table and result of the irregular wear test is shown in Fig. 6.

Table Wet limit performance Invention tire 1 115 Invention tire 2 95 Invention tire 3 ~ 110 Comparative example tire 1 80 Comparative example tire 2 100 As can be seen from the Table and Fig. 6, all the tires according to the invention have the improved wet performance or the improved irregular wear-resistance without substantial lowering of the wet performance in comparison with the tire having tread patterns of the prior art.
Therefore, the invention can provide an improved heavy duty pneumatic tire having balanced wet performance and wear-resistance as shown in the Table -` 201856~
and Fig. 6.
It is further understood by those skilled in the art that the foregoing description is that of preferred embodiments of the disclosed tires and that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

2~

Claims

1. A heavy duty pneumatic tire for a vehicle such as a truck, bus and the like, comprising two pairs of narrow grooves spaced in a width direction and extending in a circumferential direction and a plurality of sipes formed between two narrow grooves positioned on an inner side of the width direction with a constant interval in the circumferential direction, and dimensions of the narrow grooves and the sipes fulfilling the following relations, C = (0.10-0.30) x T
W = (0.03-0.14) x T
K = (0.05-0.50) x A, where T is a width of a tread of the tire, C is a distance from a tread end to the narrow groove positioned on an outer side, W is a distance between each pair of the narrow grooves, A is a distance between the narrow grooves positioned on the inner side, and K
is a distance between the sipes in the circumferential direction.

2. A heavy duty pneumatic tire as set forth in claim 1, wherein at least one main groove extending in the circumferential direction is formed in a zone defined by the narrow grooves positioned on the inner side of the width direction.

3. A heavy duty pneumatic tire as set forth in claim 1, wherein a width d of the narrow grooves fulfills a relation d = (0.05-0.3) x h, when h = 0.072 x T, where h is a depth of the narrow grooves.

4. A heavy duty pneumatic tire as set forth in claim 3, wherein the width d of the narrow grooves fulfills a relation d = (0.1-0.2) x h.

5. A heavy duty pneumatic tire as set forth in claim 1, wherein outer surfaces of ribs defined by the two pairs of the narrow grooves are radially inward of surfaces of other ribs formed in the tire.

6. A heavy duty pneumatic tire as set forth in claim 1, wherein a depth t of the sipes fulfills a relation t = (0.6-1.0) x h, where h is a depth of the narrow grooves.

7. A heavy duty pneumatic tire as set forth in claim 1, wherein an angle .THETA. of the sipes made with an equatorial plane of the tire is within 0°-90°.

8. a heavy duty pneumatic tire as set forth in claim 1, wherein protrusions are formed in the sipes therealong and spaced in extending directions of the sipes.

9. A heavy duty pneumatic tire as set forth in claim 1, wherein sipes are formed in three ribs defined by the narrow grooves positioned on the inner side of the width direction and two circumferential main grooves between the narrow grooves and inclinations of the sipes relative to an equatorial plane are changed alternately with the three ribs.

10. A heavy duty pneumatic tire as set forth in claim 1, wherein widths of the sipes are uniformly widened from intermediate portions of the sipes to outer ends opening in the narrow grooves and depths of the widened portions of the sipes are narrower than those of the sipes.