TYRE WITH REDUCED NOISE AND METHOD FOR FORMING THE TYRE

Abstract: A vehicle tyre with reduced rolling noise emission. The tyre tread is provided with one or more air-permeable channels or pores (6), which serve to neutralize air pressure differences between different parts of the tread surface in road contact, for example on each side of a tread block in a tread pattern. The invention also discloses how these channels or pores can be created by piecewise vulcanization of rubber or plastic balls, or otherwise shaped rubber or plastic bodies of which the tread is built up so that communicating channels or pores remain between such bodies.

Description: TYREWITHREDUCEDNOISEANDMETHODFORFORMINGTHETYRE The present invention concerns a vehicle tire with reduced rolling noise emission and a method for its manufacture. A considerable environmental problem in todays society is noise emission from roads and streets. At lower speeds and high acceleration, the noise from the power unit dominates at the receiver point in most cases compared to the rolling noise. At speeds exceeding 50 km/h, however, rolling noise created by the tire contact with the road will do »minate. This means that a great portion of the noise problems that exist along streets and roads even in urban areas are caused by tire/road noise. For those areas it would not help much to further re¬ duce the noise emission from the power units. The fact that the tire/road rolling noise dominates the total noise emission for mots conditions at speeds exceeding 50 km/h contributes to a certain understandable disinclination of car manufactu¬ rers to further reduce the noise emission from the power unit. A reduction of the tire/road rolling noise would thus contri- bute directly to solve noise problems at streets and highways where speed is higher than 50 km/h and also contribute to a general reduction of the road traffic noise at lower speeds, as reduced rolling noise would increase motivation also for power unit noise reduction. There are mainly three known me- thods up to now on how to reduce tire/road rolling noise. 1. Changing the tread pattern. The length of different tread blocks is varied in the direction of rotation so that the tonal components of the noise emission is spread around the mean frequency. 2. Changing the rubber compound so that higher compliance is obtained. 3. Influencing the texture of the road surface to obtain an optimal texture depth with respect to noise. The first method can probably not give any further noise re- duction because of an already well developped technique. The tonal contribution to the total noise emission is less domina¬ ting for coarce road surfaces, as the random road surface ex¬ citation of the tire would dominate noise emission in these cases. The second method can not be used without some increase of tire wear. It gives noise reduction but is not acceptable from an economical point of view. Laboratory studies have shown that the most probable cau- se of the far field tire/road rolling noise at higher frequen¬ cies is that tread block oscillations can excite air-resonan¬ ces in acoustical resonance circuits between the tire and the road surface. A method to prevent this is to allow the air pressure differences in tread cavities to be neutralized through the tread pattern. This can be done by decreasing the tread block sizes and ensure that the air can move in open and communicating channels between the tread blocks. However, if the tread blocks are too small the road holding capabilities will decrease to an unacceptable level. The proposal according to the present invention is in contrary to make the tread blocks in a shape acceptable for road-holding or other requi¬ rements but make the entire tread with communicating air chan¬ nels or pores, for example by using a porous rubber compound, or by drilling or in some other way forming holes through the tread blocks during or after manufacture. Thereby air-pressure neutralization through the tread block itself can occur while the tread stability is maintained. Due to the porosity the damping characteristics (mechanical losses) of the rubber is increased which is a further advantage with respect to tire/ road rolling noise emission. When a tread block is suddenly accelerated and decelerated during road contact, the aerody- namically stored energy is released in form of acoustical energy. If the tread block itself is porous, a part of the energy could be absorbed by the friction losses in the pores and thus not radiated to the surroundings. When the tread sur¬ face is made porous the radiated noise to the external far field will be reduced because 1) radiation efficiency will be reduced, " 2) the vibration level in the tread blocks is reduced, and 3) the stored aerodynamical energy will be absorbed during velocity changes. An important question is how a tire with a porous tread surface could be manufactured in an economical way. There are several alternative methods. A tread could be manufactured by pre-vulcanization. This means that the vulcanization process is not completed. In this pre-vulcanization process the tread is built up by a great number of rubber granules, for example balls or gra¬ vel like parts of a suitable hardness. The rubber granules are allowed to bind togehter to a certain extent by the pre- vulcanization process. During the tire manufacturing process this pre-vulcanized tread is treated in a normal way, which means that it is put on the un-vulcanized tire carcass and put into ordinary tire vulcanization machine moulds. Thereby the whole tire structure is vulcanized at the same time as a tread pattern is formed in the tread rubber. As an alternative an un-vulcanized tire carcass can be put into a mould in a vulcanization machine. Thereafter rubber - or plastic - granulate (in form of balls or other-wise shaped rubber fragments) in lose form is poured into the mould. Then the tire is vulcanized into its final shape. The quantity of rubber granulate and its size distribution is in either case choosen so that a sufficient extent of open pores is obtained. A side effect of interest from road holding point of view is that the drainage capability of the tire tread surface is drastically increased. Thereby the road grip on a wet road surface is considerably increased. In connection herewith it is worth noticing that the purpose of most tread pat¬ terns is to get a sufficient grip on wet road surfaces. On dry surfaces a sufficient grip is obtained with blank or bald tires without any tread patterns at all. Two embodiments of the present invention will now be de¬ scribed under reference to the annexed drawings, wherein fig. 1 in perspective shows a part of a radially sectioned tire ac¬ cording to a first embodiment, and fig. 2 shows a part of a cross section through the carcass and tread of this tire. Fig. 3 is a view similar to that of fig. 1, but showing a tire according to a second embodiment of the invention. Fig. 4 shows a perspective sectional view along line IV-IV in fig. 3 of this tire. ^ BJR t ^ C-PI In the drawings, 1 represents a tire carcass and 2 the tire tread. In the embodiment according to fig. 1 and fig. 2 the tread surface consists of a multiplicity of, by vulcani¬ zation interconnected rubber or plastic balls or other types of fragments, between which are communicating air spaces as for example air-permeable channels or pores. Of special impor tance is that air communication is established between a lea¬ ding 5 and trailing 6 side of tread blocks 4. In the embodi¬ ment shown in fig. 3 and fig. 4 communication between the lea ding 5 and trailing 6 edge of the tread block 4 has been crea ted by boring in the tread block 4 or by other means forming at least one covered channel 7 (i.e. not open to the tread su face like a tread groove) which is open in both ends. Forming of such channels could for example take place at the vulcanization of the tire by placing suitably shaped cores in the carcass. After the vulcanization process the cor are removed from the tire.

Claims: (received by the International Bureau on 19 November 1979 (19.11.79)) 1. A vehicle tire, the tread block (4) of which is provi¬ ded with air-permeable channels covered against the tread sur¬ face (2) , said channels allowing atmospheric air flow through a tread block (4) between its leading and trailing sides (5, 6) as seen in the rolling direction, c h a r a c t e r i z e d i n that the channels comprise intercommunicating pores be¬ tween rubber or plastic granules inter-connected by vulcaniza¬ tion. 2. A method of manufacturing a vehicle tire, the tread surface of which is provided with a multiplicity of air-per¬ meable channels or pores, c h a r a c t e r i z e d i n that the tread is built up by rubber or plastic balls or other¬ wise shaped bodies, which have been connected to each other by vulcanization such that between the bodies remain communi¬ cating spaces, which together form the communicating pores or channels. 3. A method according to claim 2, c h a r a c t e r i ¬ z e d i n that the tread surface is pre-vulcanized, so that the balls or otherwise shaped rubber or plastic bodies to some sufficient extent adhere to each other, whereafter the tread in an ordinary way is mounted on an un-vulcanized tire carcass for final vulcanization. 4. A method according to claim 2, c h a r a c t e r i ¬ z e d i n that an un-vulcanized tire carcass is put in a mould in a vulcanization machine and that lose, un-vulcanized rubber or plastic balls or otherwise shaped rubber or plastic bodies are poured into the vulcanization mould, whereafter the tire is vulcanized to its final shape.

Inventors: NILSSON N
Applicants: IFM AKUSTIKBYRAN AB, NILSSON N
Application year: 1979
Main classification: B29H5
IPC codes: B29D30, B60C11