NZ215515A

NZ215515A - Pneumatic tyre tread divided by two zig-zag circumferential grooves and a narrow groove with stepped bottom

Info

Publication number: NZ215515A
Application number: NZ21551586A
Authority: NZ
Inventors: Fujii Syouichi; Kakumu Kiichirou; Oosugi Takao
Original assignee: Sumitomo Rubber Ind
Priority date: 1985-03-19
Filing date: 1986-03-18
Publication date: 1988-03-30
Also published as: AU584399B2; DE3609248A1; AU5482586A; JPS61215102A

Description

?155 1 5 rviofity D2?c(s): ; ' 3 S, •; o c I f i c a 110 ri F 4 e d: • Pft&uf o& <o ..'2Q2> M»». i. - PATENTS FORM NO. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "A PNEUMATIC TIRE HAVING A REDUCED NOISE GENERATION1 i7 WE SUMITOMO RUBBER INDUSTRIES, LTD. of 1-1, Tsutsuicho 1-chome Chuo-ku, Kobe-shi, Hyogo-ken Japan, a Japanese company hereby declare the invention, for which -I-/we pray that a patent may be granted to we/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- E * r -i- ( '~18MAR!986^j followed by 215515 A PNEUMATIC TIRE RAVING A REDUCED NOISE GENERATION BACKGROUND OF THE INVENTION This invention relates to a pneumatic tire having a rib pattern which makes it possible to suppress noise propagation without loss of wet grip property.

To confront the ever increasing noise trouble due to speed up of automobile and expansion of high way net work in recent years, the noise control by the environmental authority has been strengthened more than ever. As is known, noise propaganda from automobile is nearly falls into 3 categories : engine-, cooling fan- and tire noises. Of these, tire-noise becomes larger, the higher the travelling speed tend to be and It is nowadays a pressing theme how to cope with the problem of noise suppressing particuraly under present circumference where road net work has been significantly modernized.

Under-lying mechanism of tier noise propagation is classified as follows : (1) Pattern noise Tread design consists mainly of those design elements which are arranged continuously and repeatedly in the circumferential direction of the tire. This design inevitably leads to a phenomenon that air trapped within the grooves of tire tread is subjected to compression followed by expansion along with the rolling motion of tire. In addition, pulsating vibration produced at the element, while in running, causes a density wave in the environmental atmosphere, which is known as pattern noise. w Z155 1 5 As procedure known as variable pitch method makes it possible through modifing pattern pitch -- the minimum element of repeating pattern -- to disperse the pattern noise over a wider range of frequency band, to suppress noise, and to preclude amplification of noise due to resonance effect. (2) Resilience - Vibration noise Irregular road surface and irregularity inherent to tire (variation in tread thickness and curvature) causes a j periodic shock, i.e. a vibration of rolling tire, which in turn produces a density wave as noise propagation within the environmental atmosphere. (3) Squeak, slip-noise A rolling tire releases a noise due to eventual slip motion between tread and ground surface or squeak due to slip against ground in the event where tread deforms at both ends of ground contact surface.

Until recently it was attempted to suppress noise as such particularly in case of rib-pattern through the following measures : 1. Reduction in the number of main longitudial groove extending in the circumferential direction ; 2. Reduction in zigzag angle of main longitudinal groove; 3. Reduction in width and depth of major longitudinal grooves.

However, the above measure is made feasible only at the cost of wet grip property of tire and consequently the effect it can afford cannot but be a limited one. 2 11 55 1 BRIEF SUMMARY OF THE INVENTION It is an object of the invention to provide a pneuaatic tire having a reduced noise generation, which aakes it possible to suppress the noise level at the saae tiae to aaintain the net grip property practically unchanged.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a enlarged front view showing right-half of the tread of one eabodiaent of the tire according to this invention ; Fig. 2 to 4 are sectional views taken along the D-D line of Fig. 1 ; Fig. 5 is a diagraa showing the zigzag angle of narrow groove in contrast to the noise level resulted : Fig. 6 is a diagraa showing the relationship between W1/W2 and noise level ; Fig. 7 is a front view showing the tire of prior art ; Fig. 8 is a front view showing the tire according to this invention ; and Fig. 9 is a diagraa showing the relationship between speed and noise level.

DETAILED DESCRIPTION A pneumatic tire having a reduced noise generation, comprising: a tread provided with two longitudinal zigzag main grooves (G) extending to the circumferential direction of the tire and at least one of a narrow longitudinal groove (g) extending to the circumferential direction; the zigzag angle (Q) of said longitudinal zigzag main grooves (G) being within a range of 0°-© relative to the circumferential direction of the tire; the groove width (Wl) of said narrow longitudinal groove (g) being 2155 1 5 over 1 ■■ and under 50X of the groove width (W2) of said main longitudinal groove (C): the groove base profile of said narrow longitudinal groove (g) having difference of level to the circumferential direction of the tire.

Details of the invention is explained hereinafter using an eabodiaent with reference to the acconpaning drawings.

The tire eabodied under this invention is provided with two longitudinal zigzag sain grooves (G) and two narrow grooves (g) arranged axial ly outside the grooves (G), both extending in the ] circumferential direction in zigzag node. 1 The zigzag angle 0 of said Main groove (G) is 0° to 30°. It O 1 is evident from the Fig. 5, showing the zigzag angle 0 of the ■ain groove (G) in contrast to the resulted noise level, that the noise level will rise abruptly when 8 exceeds 30°. In addition, deviation fro* reference noise level of plan tire is taken on the graph of Fig. 5.

The groove width (Wl) of said narrow groove (g) shall be less than 502 of the groove width (W2) of said Main groove (G) but aore than 1 mm, in other words, where W1/W2 X 100 exceeds 50?, the influence of air punping noise becomes larger resulting in an elevated noise level. In contrast, where narrow groove width were less than 1 mm, unwanted squeal noise, being specific to siping, would result.

From Fig. 6, where W1/W2 is contrasted to the noise level, it appears that the noise reaches the minimum level where W1/W2 is equal to 1/3, whereby the noise level will increase whenever W1/W2 becomes either larger or smaller than 1/3.

Like Fig. 5, the deviation from the reference noise level of plain tire is taken on the ordinate.

Further, the narrow groove (g), in this embodiment, 1 55 incorporates a groove-bottom configuration having steps in the circumferential direction.

In Fig. 2 showing the sectional view taken along the D-D line in Fig. 1. The narrow groove (g) is provided with 3 steps in the circumferential direction of the tire, whereby the groove depth (dl) of the first step groove shall preferably set within a range of 1/6 to 1/2 of depth of the iiain groove. \ shallow groove is found to effectively reduce the air puaping noise, but it gives an adverse effect on the wet grip property where it is Made excessively shallower.

In view of this antinomy it is proposed that above-Mentioned narrow groove is provided with Multiple steps, yet the depth of the first step groove is Maintained within the above Mentioned range, so that a compromise is reached between two factors of wet grip property and noise level.

According to the invention, it is possible to provide the narrow groove (g) with 3 steps as in Fig. 2, to provide the groove (g) with 3 different depths (dl,d2,d3) in different location in the longitudinal direction of groove as in Fig.3, or to provide the groove (g) with 2 steps as in Fig. 4 ; and to arrange the narrow groove (g) axially inside the main groove (G) as in Fig. 8.

In addition, for being able to maintain desired wet grip property, it is required to have the total length of the first step groove'is within a range of 1/3 to 2/3 of total length of the narrow groove in circumferential direction.

( Embodiment of the invention ) Tires of 7.00-15L/7 in size with the specification in Table 2 was experimentally manufactured using such tread patterns as shown in Fig. 7 and 8.

Table 1 215515 Control Embod iment Tread pattern Fig. 7 Fig. 8 Longitudinal main groove : Number 2 2 Groove width (mm) 6.5 6.0 Groove depth (mm) .3 .5 Zigzag angle 23° 23° Narrow longitudinal groove : Number 2 2 Width of groove (mm) 6.5 2 Depth of groove (mm) 11.0 d 2 = 7 d 1 * 2 Ratio of total lengths of the first step groove to total length of narrow groove 0 1/3 The above tires were subjected to a series of coasting noise tests under the provisions in JASCO C606. of which results are tabulated in fig.9.

From the figure, it can be verified that the embodiment of this invention showed a lowered noise level in the speed range fro* 40 to 55 km/h.

( Effect of the invention ) The rib patterned tire according to this invention is provided with the narrow groove, extending in the circumferential direction, having multiple steps running in the longitudinal direction, which makes it possible to suppress the noise level at the same time to maintain the wet grip property practically unchanged. 6

Claims

215515 41 WHAT WE CLAIM IS:

1. A pneumatic tire having a reduced noise generation, comprising: a tread provided with two zigzag wide grooves (G) extending in the circumferential direction of the tire and at least one narrow groove (g) extending in the circumferential direction; the zigzag angle (Q.) of said zigzag wide grooves (G) being within a range of 0° - 30° relative to the circumferential direction of the tire; the O groove width (Wl) of said narrow groove (g) being greater than 1 mm and less than 50% of the groove width (W2) of each said wide groove (G); the groove base profile of said or each narrow groove (g) being stepped relative to the — circumferential surface to the tire to provide the groove base with at least a first step and a second step deeper than said first step.

2. A pneumatic tire according to claim 1, wherein the depth (dl) of said or each first step is between 1/6 and 1/2 of the depth of each wide groove (G).

3. A pneumatic tire according to claim 2, wherein the total length of said first step or steps in said or each narrow groove is between 1/3 and 2/3 of its total length.

4. A pneumatic tire according to claim 1, wherein said at least one narrow groove is arranged between said wide grooves- . . /Aw o'X

5. A pneumatic tire according to claim 1, whesaan L *<-> said at least one narrow groove extends zigzag in theJJ^ circumferential direction of the tire. ™ ^

6. A pneumatic tire substantially as hereinbefore described with reference to the figures 1, 2, 3, 4 and 8, .-7.. BALDWIN, SON &CAREY A^fcC^neyC fo? the Applicants