NZ212987A - Pneumatic tyre:depthwise crooked sipes with varying bent in axial direction - Google Patents

Description

2 12987 Priority Oate(s): Complete Specification Filed: Class: &IP,, ff.

Publication Date: ...... ?.9.0jQT.l286...

P.O. Journal, No: ...../. i"?. $*. & PATENTS FORM NO. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "PNEUMATIC TIRE" -i, WE SUMITOMO RUBBER INDUSTRIES, LTD. of No.1-1, Tsutsuicho 1-chome, Chuo-ku, Kobe-shi, Hyogo, Japan, hereby declare the invention, for which i/we pray that a patent may be granted to sae/us, and the method by which it is to be performed, to be particularly described in and by the following statement (fol lowed by page I A.) 1 29 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 problem and which still have a 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 sipings S defined in the freed surface and arranged at spaced intervals along main tread grooves G. Each of the siping 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 sipings 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 traction capabilities. As shown in Fig. 2 the conventional sipings extends substantially perpendicularly to the ground-contacting surface GT of the tire and has a substantially straight cross-sectional shape. - 14%r The braking performance of the tire is increased by increasing the number of sipings in the tread and also increasing the depth, width or length of the sipings S.

However, the wear-resistant capability of the tire is reduced if the sipings 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 in rotation, the sipings 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 sipings as elastically deformed is larger. The inventor studied the relationship between the cross-sectional shape of a sipings and the deformation of the tread, and proposed to improve the braking-.driving performances and the appearance of the tire without sacrificing the wear-resistant capability by employing sipings of a bent cross-sectional shape.

Summary of the Invention It is an object of the present invention to provide a pneumatic tire having sipings shaped such that the movement of the tread rubber is more increased than sipings according to the prior art while the tread is in contact with the ground and air can effectively be removed from a mold when the tire is vulcanized in the mold with the sipings formed by knife blades.

According to the present invention, a pneumatic tire has sipings formed in a tread thereof and each having a cross-sectional shape bent in a depth-wise direction thereof and varying its bent width in an axial direction of the tire.

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 pneumatic tire; Fig. 2 is a cross-sectional view of a conventional siping ; Fig. 3 is the fragmental cross sectional views of a siping according to the present invention, each view corresponding to a cross-sectional view taken along lines A-A, B-B, C-C and D-D of Fig. 1," and Fig. 4 is the fragmentary cross-sectional views of another siping according to the present invention, 2 1 2 9 each view corresponding to a cross-sectional view taken along lines A-A, B-B, C-C and D-D of Fig. 1.

Description of the preferred embodiment Fig. 3, Fig. 4 show in fragmentary cross section two sipings, illustrating a siping S defined in the tire tread. Fig. 3 and Fig. 4 correspond to the fragmentary cross-sectional views taken along lines A-A, B-B, C-C and D-D of Fig. 1. Section A-A corresponds to an opening and SB of a siping S debouching into a longitudinal groove G, on the other hand, section D-D corresponds to a blind end SE of a siping S terminating at the central area of the rib.

A sectional shape of sipings according to the present invention is substantially straight at the opening end SB and has a bent portion B1 at the blind end SE. That is, Sipe S has a sectional shape whose bent portion varies in bent width (m^, 1112) from the opening end SB to the blind end SE, the bent width mj, IR2 of the bent portion of siping S are to be less than 6.0 mm, when it is over 6.0 mm, it tends to induce cracking failure due to abnormal deforming stress and it become difficult to form sipes on the tread rubber. Moreover one siping S requires at least one bent portion.

The siping S has a region SH closer to the tread t surface and a region SK remoter from the tread surface. 2:129 It is preferable that the regions SH, SK extend substantially perpendicularly to the groundr-oontacting surface GT of the tire.

This is because when the tire tread contacts the ground while the tire is being rotated, the oposite edge portions of the tread which define the siping S therebetween are elastically deformed in a direction normal to the ground-contacting surface GT of the tire, and the opposite edge portions can possess a sufficient strength or resistance against wear if they are formed in the same direction as that of the deformation.

Moreover, the depth of a sipe is normally defined to be a range of 50% to 110% of the depth of the longitudinal grooves G, but in other cases, the siping can be formed so as to decrease its depth from the opening end SB to the blind end SE.

As shown in Fig. 4, the bent portions B3, B4 of the siping S are formed to have gentle curved faces, jn this case, the stress induced by the repeated deformation of the tread surface can be effectively mitigated to decrease the cracking failure of the tread rubber.

According to the invention, the sectional shape of the siping S at the opening end SB is formed to be substantially straight. This is because the damage of tire appearances by air entrainment during vulcanization can be avoided by such a straight one. When this air retention , ; 2.129S or entrainment can be solved by another means, said straight shape at its opening end is not necessarily required.

Sipings according to the present invention can be so arranged on both edges of the tread or on the rib edges along the circumferential longitudinal grooves of the pneumatic radial tires for heavy duty vehicles as sipings according to the prior art are, and it is adopted for the object to prevent the uneven wear on the tread of block patterns, rib-block patterns, rib-lug patterns and other patterns, it can be used on the tread of the recapped tires.

Moreover, to form the said sipes on the tread surfaces, knife blades with a bent cross sectional shape are placed in a vulcanizing mold to produce sipings in the tread at the same time that the tire is vulcanized, this procedure is just in the same way as that to form sipings with a conventional shape.

According to the present invention, the sipe has not only a bent cross sectional shape but also such a cross sectional shape as its bent width changes from its opening end with a straight shape toward the blind end as described above.

Therefore, the tire tread has more mobility than that of the conventional tires having straight sipings, and there is no defect in appearance of tires as compared 2 1298 with that of the conventional tires having straight sipings. This is because air retention or entrainment can effectively be removed from a mold when the tire is vulcanized in the mold with the sipings formed by knife blades according to the present invention, and the braking and traction performances of the tire can be improved by a fewer number of sipings than the conventional tires, without sacrificing the wear-resistant capability. The sipings of the invention is also advantageous in that it can improve the braking and traction performances since the surface level difference L (as shown in Fig. 2) between the tread edge portions on both opposite sides of the siping occurring „ when the tire contacts with ground is much greater than that with the conventional straight sipings.

While the sipings have been illustrated as extending parallel to the axial direction of the tire, the sipings 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. 212987

Claims (4)

WHAT WE CLAIM IS:

1. A pneumatic tire comprising a tread having sipings formed in a surface thereof, each sipe having at least one bent portion in a depth-wise direction of the sipings, and the amount of offset of the bent portion changing in the width direction of the tire.

2. A pneumatic tire according to claim 1, wherein said bent portion is offset from the remainder of each sipe by 0 to 6.0 mm.

3. A pneumatic tire according to claim 1, wherein each sipe has an end opening into a circumferential groove of the tyre and the cross-sectional shape of said sipe at the open end is straight.

4. A tire substantially as herein described with reference to Figures 1 and 3 or Figures 1 and 4 of the accompanying drawings. BALDWIN, SON & CAREY ATTORNEYS FOR THE APPLICANTS