NZ214062A - Tyre tread: central tread ring with blind grooves flanked by tread blocks - Google Patents

Description

2 1406 Priority Datei'sJ: Complete Specification Filed: Class: ......

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P.O. Journal, No: "N.4 PATENT QFFCE -4 NOV 1985 RECEIVED PATENTS FORM NO. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "TIRE TREAD PATTERN HAVING REDUCED NOISE LEVEL" I-, WE 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 vdiich i/we pray that a patent may be granted to me/us, and the method by vrfiich it is to be performed, to be particularly described in and by the following statement:- 2 14062 This invention relates to a low noise tire and more particularly to a block-pattern radial tire designed to produce less air pumping and impacting noise.

[Prior Art] With the spread of an expressway network of late, the noise made by motor vehicles traveling at high speed has come to be treated as one of the problems associated with environmental pollution and particularly the tire noise is an important factor causing automotive noise. The noise caused by the tire is classified into the following according to its sources: (i) Pattern noise A space or cut groove formed in the surface of a tread is deformed when the tread touches the ground and its volume is suddenly compressed, whereby the air therein is discharged or sent out with pressure. On the other hand, the volume is sharply increased at the time the space or cut groove is released from touching the ground and it attempts to suck the air in. The air periodically sent into and out of the space or cut groove with pressure produces a continuous pressure wave, that is, sound energy. Accordingly, there appears the peak of sound energy at the frequency corresponding to the pattern pitch and it becomes the source of noise. (ii) Resonance noise This is related with the mass distribution and the - 2 14062 elasticity characteristics of a tire and they acr to produce noticeably amplified vibration depending on the speed and traveling condition of the tire, causing various parts thereof to vibrate in response to vibration-generating energy given to the tire in repetitive time sequence. Provided that the pattern pitch is so arranged that the resonance frequency of the tire conforms to the peak, vibration frequency of the tread, pattern, the resonance action thus produced increases the sound. (iii) Vibration sound due to slipping This sound is produced when the various portions of a tread slip on the surface of a road.

Attempts have been made to minimize the aforementioned causes of noise and, as for the pattern noise, for instance, there has been adopted the variable pitch method wherein the arrangement of pitch elements providing a basis for repeating the tread design has been improved so as to reducing noise by dispersing the sound energy appearing at a particular frequency throughout a wide frequency range. In this method, the pitch elements having different lengths are properly arranged in combination and the peak of sound energy periodically generated while the tire is rotated is shifted in terms of timing to lower the peak value by causing a phase difference; this is based on the so-called theory of frequency modulation. 2 14062 With respect to the resonance noise and what is caused by slipping, it has also be attempted to decrease noise by improving the structure of a tire, the quality of material used forthe carcass belt layer, the tread rubber compound and the tread pattern.

[Problems to be solved by the Invention] The aforesaid variable pitch method has disadvantages including bringing about the difference between the rigidities of pitch elements, badly affecting vibration characteristics while a tire is rotated, allowing the uneven wear of the tread and causing the life of the tire to be decreased.

The present invention is intended to provide a tire having reduced noise generation by decreasing sound energy itself of air-pumping sound or impacting sound caused by lateral grooves of radial tires provided with block type tread pattern.

(Means of solution of the Problems] The technical problems as above described can be solved by the following means: A pneumatic tire is designed so as to comprise a tread pattern provided with at least two longitudinal grooves extending to the circumferential direction of a tire and with slots, of which one end is blind and other end debouches into the said longitudinal grooves, and lateral grooves ' illlb. extending from one longitudinal groove to the other one, the length Zs of said slots to the axial direction is less than 50% of the length Jim of said laterial grooves, and the longitudinal length Ps between each centerlines of said slots and said lateral grooves is defined in a following range: (n + x 9?0 " 4 xU9 00 < Ps < (n + |) x + 4 x 900 U - V x 106 60x60 where U is expressed in mm/sec and 900 expressed in Hz.

(V means the vehicles speed at 35 kia/h or 55 km/h, and n is an integer of zero, 1/ 2 ) Brief Description of the Drawings: Fig. 1 is a partial plan view of the tread pattern- Fig. 2 is a graph showing an acoustic pressure wave form chart.

Figs. 3(A) and (B) are schematic view of tread patterns.

Figs. 4(A) and (B) and Figs. 5(A) and (B) are graphs representing acoustic pressure waveform charts.

Fig. 6 shows the drawings representing the relative position between lateral grooves and slots.

Fig. 7 is a graph showing a relation between a sound pressure level and a frequency.

Reference characters: 2...slot, 3, 4 ... lateral grooves, G1, G2, G3, G4 ... longitudinal grooves, is ... slot length, £m ... length of lateral groove, Ps ... space between slot and lateral crroove 214°6 Rererring now to the drawings, an embodiments of the present invention will be described.

In Fig. 1, a tread is provided with four longitudinal grooves (Gl, G2, G3, G4) extending to the circumferential' direction of the tire, and slots 2 debouching into said each longitudinal grooves, and inner lateral grooves 3 communicating with said longitudinal grooves being adjacent to each other in the central part of the tread, and outer lateral grooves 4 communicating with the tread edge parts through the longitudinal grooves Gl, G4 respectively.

It is necessary that the width (ts) of said slot is less than 50% of the width ( <.m) cf said lateral grooves. 2 1406 f | There are noise regulation for the constant running speed noise and the accelerated running noise about tires, to measure the tire noise generation in conformity with the tii noise tert method at coart down as provided for in JA50 C6C6 and sound collector microphone was set just besides the tire 50cm apart from the center of tire width at a height of 15 cm above the surface of the ground touched by the tire, there .j are a peak of the main acoustic energy waves in the range of 800 - 1000 Hz, as can be seen clearly from Fig. 2, the sound of 800 - 1000 Hz is largely induced by the arrangement of lateral grooves, then, the said peak value of acoustic energy waves generated by said lateral grooves in the range of 800 to 1000 Hz can be reduced by arranging said slots 2 at the said position with the prescribed length. Each v ! 1' J acoustic energy waves of the tread patterns as shown in Fig. 3(A) and Fig. 3(B) are shown in Fig. 4(A) and Fig. 4(3) respectively, the tread pattern as shown in Fig. 3(B) is of appending slits S to the tread pattern with lateral groove L as shown in Fig. 3(A) , wherein slot length is is 15 mm, : space Ps between lateral groove and slot is 6 mm and length | of lateral groove is 40 mm, the test results are to be i obtained under the running speed of 40 km/h. j Moreover, each acoustic energv waves of the modification I ^ f pattern, which space Ps between lateral groove and slot 2 14062 is changed to 12 mm in the tread pattern as shown in Fig. 3(B), and of the tread pattern as shown in Fig. 3(A), which are measured under the running speed of 8 0 km/h, are shown in Fig. 5 (B) and (A) respectively.

As apparent from the results of the above said figures, the reduction of acoustic energy can be seen by the arrangement of slots.

The space Ps between lateral groove and slot means the shortest space between them included in the same longitudinal grooves.

Generally speaking, the longer the length of slot, the larger the acoustic enercry, accordingly, it can be thought that the effect of interference become higher, when the length of slot falls in with the length of the lateral groove.

However, the effect of interference is varied in its power in accordance with running speed, so, at the speed in which the effect of the interference is small, the slot is to work adversely so as to generate its noise higher, accordingly, in order to maintain the said effect of interference higher with balance at the ordinary running speed of 30 - 70 km/h, it is necessary that the slot length Is is set up less than 50%, more preferably in the range of 10 to 403 length of the length im of lateral groove as prescribed before, and 2i406Z each length im of lateral groove 3 of inner side portion and that 4 of outer side portion can be well made in different length, in this case, the length of each slots is to be preferably adjusted in accordance with each length of lateral grooves. There is no problem to the interference effect between both factors, even if slit is disposed at the same side as the lateral groove or at the opposite side with the longitudinal groove as a center.

It is preferable to arrange the space Ps of slots so as to get out of touch with j phase between acoustic waves which each sounds in the range of 800 - 1000 Hz, namely, it is necessary to satisfy the following equation. , 1% u u 1, u U (n + j) x 90Q - 4 x 900 < Ps < <n + 2) x gQ0 + 4 x g0Q y _ V x 106 60x60 where U is expressed in mm/sec and 900 is expressed in Hz. V means the vehicles running speed, n is an integer of Zero, 1, 2, The above equation is a function of the running speed, it is necessary to have the interference effect at the specific running speed. In the noise regulation, the object of regulation is the noise generation at the ordinary runninc soeed of 3 5 km/h and at the accal^s«=feion speed of accut 55 km/h, therefore, the positions, ijj^tfhich thtf^lots are « ZA ,5*MA//988<; ;- 9 - V* ' 2 1406 i to be arranged relatively to the lateral grooves at running | speed 35 km/h, are shown in Fig. 6, wherein by arranging the slots in the below parts with oblique lines to bring ' ]_ about getting out of touch with j phase in the acoustic energy waves to the lateral grooves, so it can be expected to <-i contradict the acoustic energy waves each other by the i said interference effect. s. - • Furthermore, said n was restricted to be 0, 1, 2, this is because the interference effect cannot be expected by the way of bringing about getting out of touch with the acoustic waves between the lateral grooves and the slots, in the case that the difference in positions between the lateral grooves and the slots is more than 24 wave lengths.

Test tires 205/60R15 is size with the tread pattern (the embodiment 1) as shown in the developed view of Fig. 1 and the same tread pattern (the comparative tire 1) as that in Fig. 1 except slots were prepared by way of trial and their acoustic energy were measured in an anechoic room with an inner pressure of 2.0 kg/cm and a load of 400 kg.

The acoustic energy was measured in conformity with the tire noise test method as provided for in JASO c 6 06 and a sound collector microphone was set just besides the tire 7.5 ci apart from the canter of tire width at a hight of 1.5 m above the surface of the ground couched by l 1 V 0 62 the tire.

Fig. 7 is an acoustic pressure waveform chart in the case of above two tread pattern.

As apparent from the results of Fig. 7, the tire having a tread pattern according to the present invention can reduce the noise generation level.

[Effect of the Invention] As set forth above, slots with, the specific length arranged in the prescribed position to the lateral grooves are provided for a block type tread pattern according to the present invention, the noise energy in the range of 800 to 1000 Hz caused by lateral groove can effectively "reduced. 214062 12

Claims (6)

WHAT WE CLAIM IS:

1. A tread pattern for a tire said pattern having at least two longitudinal grooves extending in the circumferential direction of the tire, said pattern further provided with slots each slot having one end that is blind and another end that opens into one of the longitudinal grooves, and lateral grooves extending between said longitudinal grooves the length in an axial direction of each slot (Is) being shorter than 50% length in an axial direction of said lateral groove length (£m) , said slots and lateral grooves being located respectively on opposite sides of one of said longitudinal grooves with no lateral grooves being located between said slots, and the length (Ps) between the center line of each slot and the centre line of an adjacent lateral groove parallel to said slots in the circumferential direction is defined in the following range. where u is expressed in mm/sec and 900 is expressed in Hz. where V is a vehicle speed of 35 km/h or 55 km/h, and n

2. A tread pattern as claimed in Claim 1 wherein said U 4 x 900 is an integer of zero, 1, 2 length Zs is between 10-40% of Jim. 214062 4 1 - 13 -

3. A tread pattern as claimed in Claim 1 or Claim 2 wherein further lateral grooves extend from respective ones of said longitudinal grooves adjacent the outer edges of the pattern to a respective said outer edge.

4. A tread pattern as claimed in Claim 3 wherein the length of said further lateral grooves is different to said length Is.

5. A tread pattern substantially as herein described with reference to the accompanying drawings.

6. A tire having a tread pattern as claimed in any one of the preceding claims. SUMITOMO RUBBER INDUSTRIES LTD By their attorneys Baldwin, Son & Carey