GB2160829A - Multi-siped tire for low noise running - Google Patents

Abstract

A low noise pneumatic vehicle tire has a tread with a plurality of sipes in the form of slits 9 which completely cross the tread. The slits are cut after the tread is formed so as to have substantially no width. The slits are at an inclination to the equatorial line of the tire, and at at least two different pitch spacings. <IMAGE>

Description

SPECIFICATION Multi-siped tire for low noise running Background of the invention The present invention relates to a low noise multi-siped tread tire which can reduce the noise generated during rolling of the tire by arranging the slits in an irregular pitch on multi-siped tire tread, wherein a plurality of knife cuts are provided completely acros the tread width where the tire tread contacts the road.

With recent severe requirement for lowering the noise generated by automobiles from the view of environmental standards, it is necessary to reduce the noise level generated by all parts of an automobile, including the rolling of tires.

On the other hand, there is an increasing number of rubber-tired vehicles as a result of the considerable improvement of road conditions, such as the construction of extensive super-highways. As a result, the operation of automobile transportation is expanding in a wider serivce area than before.

A vehicle is liable to encounter various kinds of weather conditions during trips, and tires are needed to make it possible to operate a vehicle in all kinds of weather conditions.

Heretofore, such rib-type pattern tires have been provided with at least two zig-zag grooves extending in the circumferential direction on the tread surface. Such tires have been widely used as a tire for operation on paved roads, like super-highways, and generally such tires provide high directional stability on a dry road and are desirable from the view point of pattern noise and fuel consumption. However, such rib-type pattern tires are regarded as inferior so far as traction, braking performance and the steering performance on wet roads are concerned. This becomes one of the problems to be solved.Thus, in order to solve the problems concerning rib pattern-type tire, tires such as block-type pattern, which can effectively remove water existing between the tread surface and the road, and multi-siped tread tires (rib-type pattern with a plurality of slits thereon) have recently beome popular. These are often callled all-weather tires.

However, such block pattern tire and multi-siped tread tire are apt to generate high pattern noise, and such block pattern tires tend to wear rapidly, so there are considerably draw-backs for such tires.

Summary of the invention It is an object of the present invention to provide a tire which can effectively eliminate the disadvantages of the prior art multi-siped tire, that is, which can effectively reduce the pattern noise with the aid of slits arranged in an irregular pitch without sacrificing the directional stability on dry roads and wet grip performance, steering stability on wet roads, resistance to wear, low fuel consumption and resistance to irregular wear.

In a preferred embodiment, after manufacture of a green (unvulcanized or partly vulcanised) tread belt, it is vulcanized to form tires with a plain tread which has no pattern thereon, or with a rib pattern tread or a block pattern tread.

Then, a plurality of closely spaced slits are cut at an inclination with respect to the equatorial line of the tire, completely crossing the overall tread width, and the slits are arranged in a combination of more than two kinds of pitch length, that is, in an irregular pitch arrangement.

In order that the invention may be more clearly understood, preferred embodiments will be explained in connection with the attached drawings, in which: Brief description of the drawings Figure 1 is a plan view of a multi-siped tread pattern according to the prior art; Figures 2, 3 and 4 are sectional views taken on lines A-A, B- B and C-C, respectively, of Figure 1; Figure 5 is a plan view of a multi-siped tread pattern for low noise according to the invention; Figure 6 is a plan view of a multi-siped tread pattern according to the prior art; Figure 7 is a plan view of a prevulcanized typical rib-type tread pattern before forming the slits thereon; and Figures 8 and 9 are graphs illustrating the results of the tests conducted to compare three patterns, as shown in Figures 5- 7, in respect of the frequency analysis values of noise level.

Description of a preferred embodiment As illustrated in Figure 1, which shows a right-half plan development view of a tread pattern 2 of a multi-siped tire 1 as one embodiment according to the prior art, and in Figure 2, which is a sectional view taken along a line A-A in Figure 1, the tire 1, according to the invention, has a tread surface 3 with a longitudinally continuous main groove 4 formed with zig-zag ribs extending in the circumferential direction of the tire on the crown region.Both shoulder regions are furnished with a tread center part 5 and a pair of shoulder parts 6 dividing the tread 2 with a main groove 4, and having a carcass ply 7 formed of a layer of radially or semi-radially arranged steel cords or fiber cords with an inclination of 60 to 90" with respect to an equatorial line C of the tire.The belt layer 8 is formed of steel cords arranged in the tread 2.

A plurlaity of slits 9, spaced apart in the circumferential direction with an inclination with respect to an equatorial line C of the tire, are positioned to completely cross the overal width of the tread 2.The main grooves 4 may be formed in the vulcanizing process by the mold or may be formed in a manner such that the plain tread is grooved by a grooving tool after prevulcanization. A torroidal green (un-vulcanized or partly vulcanized) cover tire comprises a pair of axially spaced wheel rim engaging bead regions (not shown in the drawings), a carcass layer 7 reinforced by a reinforcement ply extending from one bead region to the other bead region, a belt layer 8 arranged parallel to the ground contacting surface and a carcass ply and a tread region 2, which are all formed with each other to constitute a torroidal carcass.

This carcass is then vulcanized in a mold in a conventional manner, a plurality of slits 9 are formed in a tread vulcanized in the above-described manner by a suitable edged tool, such as a knife, a tooth of a saw or a hone having a thin blade. These slits, of a thickness under 3 mm, are produced to extend transversely across the overall width of the projection between the main grooves 4,4 of the tread 2 of the tire 1 at an inclination with respect to the equatorial line C of the tire without substantial groove width. According to the prior art, slits are formed under pressure in a mold provided with internal thin metal plates, and the cuts cannot be basically made to be a narrow width but become comparatively wide.

However, according to the present invention, the width of the said slits 9 arranged on the tread surface of the tire 1 is made to have no substantial dimensions, so that the edges on the opposite sides of each slit 9 are so strongly pressed against each other by the compressive stress generated in the contact area with ground, to function as if it is a continuous rubber layer. As a result, the rigidity on the tread is increased, whereby the wear-resistant property of the tread is improved. Furthermore, the deflective stress produced in and around the ground contacting area can be effectively enough dispersed and alleviated so that railway wear and shoulder wear of the tread edge regions can be, for practical purposes, sufficiently prevented and traction on wet roads can be improved.Both edges of the slits 9 are opened sufficiently upon tire revolution, so that the screen of water on the road is scattered to provide for free water passage towards main grooves 4 to prevent hydroplaning phenomenon.

In order to more effectively promote the aforementioned effect, the slits 9 are cut over the overall width of the tread portion 2 in a straight line and extend at an angle of 30 to 90 , more preferably 50 to 80" with respect to the equatorial line C of the tire. When the inclination of the slits 9 is too small, the improvement in the wet-grip performance and the resistance to the irregular wear becomes smaller.

Furthermore, as shown in Figures 3 and 4, a sectional view taken along the lines B-B and C-C, respectively, of Figure 1, the depth d of the slits is varied in the width direction of the tread, as shown in section B-B in Figure 3, the depth d of the slits 9 is gradually increased from the tread edge toward the tread center C, on the contrary, as shown in section C-C in Figure 4, the depth d of the slits 9 is decreased from the tread edge toward the tread center C, thus the equi-spaced slits in the circumferential direction are arranged with alterations of said two types of slits 9, which increases the depth d toward the tread center and decreases the depth d toward the tread center. The base rubber parts of the slits are so reinforced by arranging the slits as aforementioned that damage to tread rubber 2 can be effectively prevented.According to the invention, the slits, which have a constant depth in the width direction and change in depth as aforementined, can be used in combination, the depth d of the slits 9 is in the range of 50-110% of the depth d of the main circumferential groove 4.

Accordingly, how to make the slits has been mainly described hereinbefore, as the result of the inventor's various investigations in the pitch arrangements for the slits on the tread.An achievement of the invention is to provide a heavy duty pneumatic tire having a tread pattern which avoids the disadvantages of the prior art and improves the traction and braking performance on wet roads and the wearresistant property, and reduces running noises with the aid of slits arranged in an irregular pitch without sacrificing other performance. The pitch arrangement characterized in the invention will be apparent from the following description, by way of example only, of one embodiment of the invention, in conjunction with the attached diagrammatic drawing which is a part plan view of a tread pattern.

Example 1 In a tire of a size 10.00 R 20 14 PR., the circumference of the tread surface is divided into twelve equal parts whose one segment (SG) is composed of three pitch arrangements, as shown below and in Figure 5: SSSSMLMSMMSLMLLLLLSM The tread pattern for one circumference is made up by repeating the above arrangement twelve times over.

The lengths of each pitch are as shown below: Pitch Length Pitch mm The ratio of Pitch Length S (Small) 11.0 M (Medium) 13.7 M/S = 1.25 L (Large) 16.4 LIM = 1.20 Then, the ratio of pitch length S, M, L, that is, M/S and L/M are defined to be in the following range: 1.05 S M/S or UM < 1.35 When the ratio is less than 1.05, the strength of the tread rubber between these pitches becomes too small, as a natural consequence, the tread rubber tends to be damaged at an early stage; on the other hand, when the ratio becomes more than 1.35, the wet grip tends to be reduced due to the wide pitch length.

Therefore, the ratio of M/S or LIM is more preferred to be in the range of 1.15 to 1.25, and the pitch length L of the slits is in the range of 5 to 50 mm, more preferably between 10 to 30 mm. When the slits 9 are too many in number, the rigidity of the tread portion become so small that the steering stability and the wear-resistant property are liable to be reduced too much. Furthermore, the slits 9 should be formed by special machinery from the view point of productivity and manufacturing accuracy, and by auto slit processing machinery which is able to adjust the position and angle at which the slits are cut. For instance, this machine is comparable with such means as to fit a tire on its axle and as to make slits across the entire tread width and can shifts its position in the width direction on the tread surface.

As aforementioned, the tire manufacturing process according to the present invention is to make the slits on the prevulcanized tire tread, thus, it becomes possible to from such slits so as to have no substantial slit width; as the result, both lip edges of each slits are strongly forced to contact each other by compressive stress in the ground contacting area, such tread moves as if it were a continuously united rubber layer to bring about improvement of the steering stability and wear-resistant property. Moreover, the wet grip performance is improved, this is because the water screen on the road can be effectively scattered away by the aid of such slits as to be opened by the deflection of tread rubber and, at the same time, increasing the drainage efficiency toward the main grooves.

The mold for forming the tread pattern is not provided with thin metal blades which form the traverse groove. Other intricate treatments are not required in the mold cavity, thus the cost to make the molds can be reduced.Furthermore, the slits can be arranged in any type of shape and dimension according to the requirement by the users.

The present invention can be applied to any new tire with rib- type pattern, rib-lug type pattern and block-type pattern for passenger cars or heavy duty vehicles or the like, but it can be more preferably used for heavy duty pneumatic steel radial tires with a tread pattern composed to 2-5 circumferential zig zag main grooves on the tread surface.

Example 2 Steel radial tires of a size of 10.00 R 20, having the specification as shown in Table 1, were made for trial and were compared with the prior art tires for the evaluation of the noise level, wear-resistant prop erty and wet grip performance.

Results of the experiments are in Table 1, wherein values of the prior art are arbitrarily set at a scale of 100 and values of the tires according to the invention are indexed to 100.

As can be seen from the results listed in Table 1, the tires according to the invention are improved in the above-discussed characteristics in comparison with those of the prior art.

The foregoing is given by way of disclosing a preferred embodiment, but the scope of protection is limited only by the following claims.

TABLE 1 Test Tire Present Invention PriorArt Prior Art -2 Specification Tire size 1000R20 14 PR. 1000R20 14 PR. 1000R20 14 PR.

Tread pattern Fig. 5 Fig. 6 Fig. 7 Slit Slit depth (mm) 10 -5 mm - Slit width (cutter) (mm) Under 2 mm (250 mm blade) - Angle (to the quatorial line) 15 15 - Pitch (mm) 1,11,13.7,16.4 13.7 - (3 pitch) (Single pitch) Wet grip property (Note 1) &commat; lock 103 103 100 106 106 100 peak Irregular wear good good standard Wear-resistant property (Note 2) 110 112 100 Rolling-resistance (Note 3) 100 100 100 Noise level (Note 4) Ref. Fig. 8, Fig. 9 Note 1) tested by a trailer car under wet condition, the larger the index, the better the performance.

Note 2) the relative index of running distance per 1 mm wear of the tread rubber.

Note 3) tested by the rolling resistance tester.

Note 4) measured by a sound pick-up microphone standing at just one side of a car and at the distance of 7.5 m from the center line of a test car and at the height of 1.2 m from the ground in an anechoic room.

Claims (15)

1. A multi-siped pneumatic vehicle tire comprising: a pair of sidewalls and a tread area; said tread having a plurality of slits closely spaced about the circumference thereof; said slits being cut at an inclination to the equatorial plane of the tire and completely crossing the overall tread width; and the circumferential spacing of the slits being such that there are more than two different pitch spacings between neighboring slits.

2. The tire of Claim 1, in which the slits are formed after prevulcanization of the tread.

3. The tire of Claim 1, in which the slits are circumferentially equispaced between 5 and 50 mm.

4. The tire of Claim 1, in which the ratio of the lengths of two neighboring pitches is in the range of 1.05 to 1.35 when the length of a plurality of pitches are in the order of S (short) < M (medium) < L (long).

5. The tire of Claim 1, in which at least some of the slits are of varying depth across the width of the tread.

6. The tire of Claim 1, in which some of the slits have a greater depth at their axial outer ends than at the center of the tread and others of the slits have a greater depth at the center of the tread than at the axial outer end thereof.

7. The tire of Claim 5, in which every other slit has a greater depth at its axial outer end than at its center.

8. The tire in Claim 1, in which the tread is molded with only circumferential extending main grooves and the slits are subsequently cut in a separate operation.

9. The tire of claim 8, in which the depth of the slits is in the range of 50 to 110% of the depth of the main grooves.

10. The tire of Claim 1, in which the circumference of the tire is divided into a plurality of segments and each segment is circumferentially divided into at least two pitch spacings.

11. The tire of Claim 10, in which the tread surface is divided into twelve equal circumferential segments and each segment is in turn divided into an equal number of pitches.

12. The tire of Claim 11, in which each segment is divided into at least three pitch arrangements.

13. The tire of Claim 11, in which each segment is divided into at least three pitch arrangements, each having S (short), M (medium) and L (long) pitch lengths.

14. The tire of Claim 13, in which the pitch lengths are arranged SSSSMLMSMMSLMLLLLLSM in each segment.

15. The tire of Claim 1, in which the slits have no substantial width so that when in ground contact the edges of a slit are forced into firm contact with each other, such that the tread moves as if it were a continuously united layer while in the ground contact area, but the edge of a slit will separate when leaving the ground contact area.