NZ212602A - Pneumatic tyre with depth-wise crooked sipes:each sipe bridged by a spew - Google Patents

Description

2 1 Priority Date(s): .... r? Complete Specification Filed: J.'. 7.

Class: .^ £P. .

Publication Date: ..... Jl?. ^Vj.9.86...

P.O. Journal, No: c Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "PNEUMATIC TIRE" -1-7WE SUMITOMO RUBBER INDUSTRIES, LTD. of No. 1-1, Tsutsuicho 1-chome, Chuo-ku, Kobe-shi, Hyogo, Japan, a Japanese company, hereby declare the invention, for which -I-/we pray that a patent may be granted to -me/us, and the method by which it is to be performed, to be particularly described in and by the following statement (followed by page f A.) 2 f 260 TITLE OF THE INVENTION PNEUMATIC TIRE BACKGROUND OF THE INVENTION The present invention relates to a pneumatic tire having a siping of an improved shape on the tread thereof.

Spiked tires are widely used for running on snowy or frozen roads during the winter. When spiked tires run on ordinary paved roads, they tend to produce dust particles and damage the paved road surfaces. Efforts have been made to develop spikeless tires which are free of such a prblem and which still have as good braking and running performances on snowy and frozen roads as the spiked tires.

FIG. 1 of the accompanying drawings illustrates a pneumatic tire having transverse sipes S defined in the tread surface and arranged at spaced intervals along main tread grooves G. Each of the sipes S generally has a width of 1 mm or smaller and a depth equal to or smaller than the depth of the main tread grooves G-. The sipes S serve to make the tread resilient enough when it is elastically deformed in contact with the ground, thus enabling the tire to have increased braking and driving capabilities. As shown in FIG. 2, the conventional sipe extends substantially perpendicularly to the ground-contacting surface GT of the tire and has a substantially straight cross-sectional shape. The braking performance of the tire is increased by increasing the number of sipes in the tread and also increasing the depth, width or length of the - 1 Or 2 1 260 sipes. However, the wear-resistant capability of the tire is reduced if the sipes are increased in number, depth, width or length. Therefore, it has been customary to design the tires.while keeping these two contradictory characteristics in balance. The inventor has found that when the tire is repeatedly elastically deformed while it is rotation, the sipe is also deformed as indicated by the dotted lines in FIG. 2, and the braking ability becomes greater as the level difference L between the opposite edge portions El, E2 of the sipe as elastically deformed is larger. The inventor studied the relationship between the cross-sectional shape of a sipe and the deformation of the tread, and proposed to improve the braking and driving performances without sacrificing the wear-resistant capability by employing sipes of a bent cross-sectional shape. To form such a siping of a bent cross-sectional shape, knife blades are placed in a vulcanizing mold to produce sipes in the tread at the same time that the tire is vulcanized. However, where the knife blades have bent portions, difficulty arises in effectively removing air from the mold.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic tire having sipes shaped such that air can effectively be removed from a mold when the tire is vulcanized in the mold with the sipes formed by knife blades. 2U603; According to the present invention, there is provided a pneumatic tire comprising a tread having sipes formed in a surface thereof and each having at least one bent portion in a depth-wise direction of the sipe, each sipe being defined between confronting side walls which are interconnected by at least one rubber spew lying across tHe sipe.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary plan view of the tread of a conventional pneumatic tire; FIG. 2 is a cross-sectional view taken along line II - II of FIG. 1; FIG. 3 is a^fragmentary cross-sectional view of a pneumatic tire according to the present invention, the view showing a sipe .defined in the tire tread; and FIG. 4 is a fragmentary cross-sectional view of the pneumatic-±ire of FIG. 3, the view corresponding to a cross-sectional view taken along line IV - IV of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 3 shows in fragmentary cross section a pneumatic tire, illustrating a sipe SA defined in the tire tread. FIG. 3 corresponds to the fragmentary cross-sectional view taken along line II - II of FIG. 1. 2 1260 The sipe SA has two bent portions B1, B2 in the depth-wise or longitudinal direction thereof, the bent portions Bl, B2 having widths ml, m2, respectively, each in the range of from 1.0 to 6.0 mm. If the widths ml, m2 were smaller than 1.0 mm, then the tread would not be rendered sufficiently resilient, and if the widths ml, m2 were in excess of 6.0 mm, then the tread, would be unduly deformed, causing cracks in the tread surface, and it would generally be difficult to form the sipes SA. One sipe SA requires at least one bent portion,-and may have more than two bent portions.

The sipe SA has a region SA1 closer to the tread surface and a region SA2 remoter from the tread surface, the regions SA1, SA2 extending substantially perpendicularly to the ground-contacting surface GT of the tire. This, is because when the tire tread contacts the ground, while the tire is in rotation, the opposite edge portions of the tread which define the sipe SA~ therebetween are elastically deformed in a direction normal to the ground-contacting surface GT, and the opposite edge portions can retain a sufficient strength or resistance against wear if they are formed in the same direction as that in which the deformation occurs.

The sipe SA is defined between opposite side walls of the tread which are interconnected by at least one rubber spews, or three rubber spews Vl, V2, V3 as shown in FIGS. 3 and 4. The rubber spew VI is located in the region SA1, while the rubber spews V2, V3 are located in the bent 2 126 portions B2, Bl, respectively, of the sipe SA.

As is conventional_the- s.ipes. of ..the..present invention may be disposed on the opposite ends of the tread of a radial tire for use on a heavy-duty motor vehicle, or along circumferential grooves in a tire tread for the purpose of preventing the tire from being subject to localized wear. The sipes of th invention may also be formed on the tread of a tire having a block pattern, rib block pattern, or a rib lug pattern, or on the tread of a reclaimed tire.~ The sipes have a depth which is the same as or smaller than the depth of main tread grooves, and a width of 2 mm or smaller.

For forming the sipes of the invention in the tire tread surface, cutting member such as knife blades having bent portions are attached to the inner surface of a vulcanizing mold, and the sipes can be formed at the same time the tire is vulcanized in the mold in the conventional manner. The rubber spews in the sipes can be formed by using knife blades having vent holes therein.

According to the present invention, the sipe has a bent cross-sectional shape as described above.

I Therefore, the tire tread is more movable than that of the conventional tires having straight sipes, and the braking and driving performances of the tire can be improved by a fewer number of sipes than the conventional tires, without sacrificing the wear-resistant capability. The sipe of the invention is also advantageous in that it can improve the braking and driving performances since the surface level difference L (FIG. 2) occurring when the tread edge portions on both sides of the-sipe.. is_greater.-than. possible with the conventional straight sipe.

Inasmuch as the sipe has rubber spews in the vicinity of the bent portions thereof, air trapped upon vulcanicatlon._can .effectively-be-.reduced, and the tread can be vulcanized to a tread pattern as designed.

While the sipes have been illustrated as extending parallel to the axis of the tire, the sipes of the invention can be formed in the circumferential direction or in a direction oblique thereto.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be~made therein without departing from the scope of the appended claims. 218602

Claims (5)

WHAT WE CLAIM IS:

1. A pneumatic tire comprising a tread having sipes formed in a surface thereof and each having at least one bent portion in a depth-wise direction of the sipe, each sipe being defined between confronting side walls which are interconnected by at least 'one rubber spew lying across the sipe.

2. A pneumatic tire according to claim 1, wherein said bent portion is offset from remaining sipe portions by 1.0 to 6.0 mm.

3. A pneumatic tire according to claim 1, wherein dx-Ji said sipe has a region closer to the surface of the tr-a^e than the at least one bent portion and extending substantially perpendicularly to a ground-contacting surface of the tread.

4. A pneumatic tire according to claim 1, wherein said rubber spew is disposed in said bent portion of the sipe.

5. A pneumatic tire substantially as herein described with reference to Figures 3 and 4 of the accompanying drawings. BALDWIN, SON & CAREY ATTORNEYS FOR THt APPLICANT