NZ212734A - Pneumatic tyre:siping width in varying length tread blocks proportional to block length - Google Patents

Description

2 12734 Priority Date(s): ...

Complete Specification Filed: 'X'.7. Class: $<r///.#. ?A c- 5 DEC Publication Date: >* t A P.O. Journal. No: W-c . Nl V ~ PATENTS FORM NO. 5 NEW ZEALAND PATENTS ACT 1953 t f* COMPLETE SPECIFICATION \ ,A\ \ PNEUMATIC TIRE \ 1 5 J UL 1985 J W <c X^ce_V ltd I-, WE SUMITOMO RUBBER INDUSTRIES, LIMITED- of No. 1-1, Tsutsuicho 1-chorae, Chuo-ku, Kobe-shi, Hyogo, Japan (a Japanese company) hereby declare the invention, for which ff/we pray that a patent may be granted to «e/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to pneumatic tires.

More particularly the present invention relates to a pneumatic tire which reduces the generation of noise on account of a unique tread pattern consisting of a plurality of block elements of varied pitch length arranged in the circumferential direction, each block element having a siping on the surface thereof. The term "pitch length" is used throughout this specification to refer to the length of the block element.

[Prior art] The conventional tread pattern of tire consists of uniform elements arranged at equal intervals in the circumferential direction of the tire. This pattern compresses and decompresses repeatedly the air in the tire tread grooves as the tire rotates. The repeated compression and decompression of air generates compressional waves of air which are heard as the so-called pattern noise. Efforts have been made to reduce this pattern noise by arranging the tread pattern elements (or blocks) of varied pitch length. This method,however, has some disadvantages. That is, the element of the longest pitch and the element of the shortest pitch differ in stiffness, and the uneven element arrangement in the circumferential direction makes the flow of rubber on the tread row carver uneven, with the result that the thickness of the subtread becomes uneven and the vibration characteristics of tire rotation are adversely affected and uneven wear occurs.

The present invention therefore seeks to reduce the difference in stiffness of the tread block elements of 2 1273 varied lengths, and to reduce the uneven flow of tread rubber.

According to one embodiment of the present invention there is thus provided a pneumatic tire which comprises a tread having a plurality of block elements of varied pitch length in the circumferential direction of the tire, each of the said block elements having on the surface thereof a siping which differs in width from one block element to another, with the ratio of the widths of the sipings on the individual block elements being approximately equal to the ratio of the pitch lengths of the block elements to which the sipings belong respectively.

An embodiment of this invention is described by way of example and with reference to the accompanying drawing which shows very diagrammatically a partial plan view of a pneumatic tire according to the invention.

In Fig. 1, there are shown three rows of blocks at the centre of the tread. Each row consists of three kinds of block elements A, B, and C arranged periodically in the circumferential direction. These blocks differ in pitch length from one another. Block element A has the longest pitch length L; block element B has the medium pitch length M; and block element C has the shortest pitch length S. On the surface of each block element A,B, and C is made siping a,b, and c, respectively.

According to this invention, the block elements of each block row may have three different lengths L, M, and S. This reduces the noise resulting from resonance. 212734 In a Referred embodiment the ratio of the maximum pitch length L to the minimum pitch length S should be 1 to 1.6, preferably 1.2 to 1.4. This ratio is necessary to prevent the stiffness of the block elements from becominq uneven and also to prevent the flow of the tread rubber from becoming uneven at the time of vulcanization. In this embodiment, three kinds of pitch lengths are used; in another embodiment, two or four or more kinds of pitch lengths may be used. In addition, the arrangement of the pitch lengths is not limited to the order of L-M-S; but it may take any order such as LL-MM-SS as in the conventional variable pitch arrangement. In the embodiment as shown in Fig.l, the ratio of the three pitch lengths (L/M/S) of the respective block elements is 110-120/100/80-90.

The siping a, b, and c formed respectively on the block elements A, B, and C have the widths aw, bw, and cw, respectively, with aw being greater than bw, and bw being greater than cw. Moreover, the width of each siping is approximately proportional to the pitch length of the block element to which the siping belongs. In other words, the relation L/M/S = aw/bw/cw is established.

Making siping on each block element and adjusting the siping width as mentioned above make uniform the stiffness of the block elements having different lengths.^ T £ each block element. The lengths (a>-,bt, c£) of the jf | 30^P sipings (a,b,c) should preferably be proportional to * ~ r- the pitch lengths L,M, and S, respectively. The sipings J v' 2 1273 (a,b,c) are linear cuts as shown in Fig. 1; and they are formed at an angle of 0° to 90° with respect to the tire equator.

The siping is not necessarily linear, but it can be of any shape. The siping should be formed at the center of each block element, and should not extend to the edge of the block. This is necessary to prevent the stiffness of the block element from excessively decreasing.

In the embodiment shown in Fig. 1, only one siping is made on the block element; but it is also possible to make additional sipings or an auxiliary groove, with one end thereof communicating with the tread groove.

Where the tread has a plurality of block rows, at least one of the rows should meet the above-mentioned requirements for block pitch arrangement and siping.

According to a preferred embodiment of this invention, the pitch variation technique may also be applied to the widthwise grooves which separate the block elements from one another in the circumferential direction. In other words, the distance W1 between block element C and block element A, the distance W2 between block element B and block element C, and the distance W3 between block element A and block element B may be proportional to the pitch lengths S, M, and L of the block elements,respectively.

Thus, by this invention a pneumatic tire is provided which has block elements which are arranged according to the pitch variation technique and also has siping on each G O O .. ..... 212734 block element. The siping can decrease the variation of stiffness among block elements and can prevent the flow of green rubber from becoming uneven at the time of vulcanization.

Although this invention has been described by way of example and with reference to one possible embodiment thereof it is to be understood that modification or improvements may be made thereto without departing from the scope of the invention as defined by the appended claims.

Claims (8)

7- 212734 c WHAT WE CLAIM !£:-

1. A pneumatic tire which comprises a tread having a plurality of block elements of varied pitch length (as herein defined) in the circumferential direction of the tire, each of said block elements having on the surface thereof a siping which differs in width from one block element to another, with the ratio of the widths of the sipings on the individual block elements being approximately equal to the ratio of the pitch lengths of the block elements to which the Eipings belong respectively.

2. A pneumatic tire as claimed in claim 1 wherein the ratio of the minimum said pitch length to the maximuir, said pitch length is between 1:1 and 1:1.6.

3. A pneumatic tire as claimed in claim 2 wherein said ratio is between 1:1.2 and 1:1.4.

4. A pneumatic tire as claimed in any one of the preceding claims wherein there is a periodic variation in the pitch lengths of adjacent block elements about the circumference.

5. A pneumatic tire as claimed in any one of the preceding claims where at least three block elements of varied pitch length are provided.

6. A pneumatic tire as claimed in any one of the O preceding claims wherein the length of each of said sipings is approximately proportional to the pitch /V length of the respective block element. -8-

7. A pneumatic tire as claimed in any one of the preceding claims wherein each of said sipings is linear and is at an angle of between 0° and 90° to the tire equator.

8. A pneumatic tire substantially as herein described with reference to the accompanying drawing.