TYRE WITH A REDUCED NOISE LEVEL

Abstract: A vehicle tire, that radiates reduced external noise. Its inner cavity is totally or partially filled with soft rubber or plastic material (4) and its outer diameter/sectional width ratio is greater than 8.

Description: TYREWITHAREDUCEDNOISELEVEL 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 dominate. 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 most 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 ot the total noise emission is less domina- * ting for coarse road surfaces, as the random road surface ex¬ citation of the tire would dominate noise emission in these cases. The- ' second method cannot be used without some increa of tire wear. It gives noise reduction but is not acceptabl from an economical point of view. The present invention deals instead with how the tire/ro noise emission can be reduced by a combination of two simul neous measures. These are making the tire higher and narrow at the same time as the inside of the tire is filled with a soft rubber instead of air. This can be accomplished by inj ting soft rubber in non-hardened form until the tire gets t shape desired. The rubber is than kept under pressure until has hardened. These measures are not known as noise reducing measures. great number of laboratory experiments, however, revealed t when those two measures are simultaneously applied to a tir construction, combination effects arise, that reduce the ex ternal tire/road noise emission much more than what could b expected by merely adding the damping effects in dB (A 1 ) of e measure. When a tire is filled with soft rubber instead of a reduction of the level at the frequency range 1000 Hz (ba width about one octave) is obtained. This reduction is, how ever, obtained in a frequency range where the noise levels today's tire structures are already low. The soft rubber fi ling reduces the noise level in dB (A) units, but the reduct is limited because the noise levels at other frequencies th where the filling is effective will dominate the sound leve in dB(A) (see fig. 1). If now the gross dimension of the t is changed to higher and narrower, the spectrum shape of th externally radiated noise will change in a way which makes the rubber .filling more effective. By making the tire highe and narrower the dominating part of the noise at high frequ cies of normal dimension tires will be reduced. This mean that the combination of "higfeer * and narrower" with soft rub filling instead of air leads to a considerably greater redu tion of the total noise level in dB(A) compared to an addin of the total level decrease in dB(A) of each of the two mea sures. The invention will now be described with reference to th annexed drawings, wherein fig. 1 and fig. 2 show diagrams f yj f \y Λ , _V c - s an ar res, g. s ows a cross sec on roug one a of a standard tire, fig. 4 shows a cross section through the half of a tire according to the invention, and fig. 5 shows an axial cross section through a vehicle wheel with a multi- plicity of partial tires according to the invention. In fig. 1 the upper curve represents the sound pressure le¬ vel for an ordinary standard tire of dimension 175SR14 manu¬ factured by Gislaved Tire and Rubber Company and of the type "Frost Winter". The curve below represents the same tire fil- led with soft rubber instead of air. It can be seen that in the frequency range 600-1100 Hz a noise reduction of 12-15 dB- units is obtained. It can also be seen that the sound pressure level spectrum for the tire in its original design shows a dip in this frequency range. The total sound level reduction (dB(A)) is therefor reduced to only 4-5 dB(A)-units. In fig. 2 a standard passenger car tire summer tire Gisla¬ ved 175SR14 (upper curve) is compared to a high and narrow ti¬ re (curve below) . It can be seen that the noise reduction is greatest for frequencies above 1000 Hz. This leads to that the dip in the spectrum shape is lost. Thus, the rubber filling will be more effective when applied on a high and narrow tire compared to a standard tire. The tire 1 shown in fig. 3 has its inside 2 conventionally air-filled. Its outer radius is r, and its width is b, . Such a tire has an outer radius/sectional width ratio 2r,/b, which is less than or equal to 4. On the contrary the tire 3 according to the invention is in whole or partly filled with soft rubber or soft plastic mate¬ rial 4, which is softer than 35 Shore A. The outer radius of the tire 3 is r~ and its sectional width is b~- The tire accor¬ ding to the invention should have a diameter/sectional width ratio greater than 8, i.e. 2r_/b ? = *» 8. In some cases it can be difficult for certain vehicles to find a tire, that fulfills the desired outer diameter/sectio- nal width ratio without its bearing capacity and/or its con¬ tact surface to the road will be decreased. In -fig. 5 is shown how in such cases a wheel can be constructed using several ti¬ res that fulfill the above mentioned relation. The wheel OMPI , WWIIPPOO > shown includes a main rim 5, on which are arranged several sub-rims 6, each carrying one tire 7. Each tire 7 fulfills the above-mentioned requirements regarding outer diameter/ sectional width ratio and is, according to what has been pr viously said, filled with soft rubber 4 or the like instead of air. The rubber composition or plastic material used when empl ing the invention shall be a material with high loss factor and have such inner losses that the lowest external noise level (in dB(A) ) results, at the same time as the heat rele inside the rubber filling is kept within acceptable limits. The tires described could be only partially filled with r ber or plastic material. In such case the remaining part of the tire is conventionally filled with compressed air.

Claims: Vehicle tire, c h a r a c t e r i z e d i n that its inner cavity is totally or partially filled with rubber or plastic material (4) which is softer than 35 Shore A and which has been so adapted that the lowest external sound le¬ vel emission (in dB(A) ) results at the same time as the heat release at normal driving will be acceptable, and that the ti¬ re has an outer diameter/sectional width ratio (2r 2 /b„) , which is greater than 8. OMPI

Inventors: NILSSON N
Applicants: IFM AKUSTIKBYRAN AB, NILSSON N
Application year: 1979
Main classification: B60C19
IPC codes: B60B9, B60B11, B60C3, B60C7