LU503431B1 - Pneumatic tyre comprising sound absorbing device - Google Patents

Abstract

It is provided a pneumatic tyre (1) comprising: an inner surface (2), a tread portion (3), a pair of sidewall portions (4) radially inwardly extending from both edges of the tread portion (3), and bead portions (5) disposed at radially inner edges of the sidewall portions (4), and a sound absorbing device (6) made of a spongy material which is adhered to the inner surface (2) of the pneumatic tyre (1) at a tread region and extends in the tyre circumferential direction, wherein the sound absorbing device (6) comprises at least one sound absorbing member (7) with circumferential outer ends (7a, 7b), characterized in that at least one of the circumferential outer ends (7a, 7b) comprises at least one step (10), cut-out (11), recess (12), or combinations thereof.

Description

APOLLO TYRES GLOBAL R&D B.V. Düsseldorf, 3 February 2023

Our Reference: AD 42873/AL

Apollo Tyres Global R&D B.V.

Colosseum 2, 7521 PT Enschede, Netherlands

Pneumatic tyre comprising sound absorbing device

Description

The present invention relates to a pneumatic tyre comprising a sound absorbing device.

In general, there are two causes of vibrations in a vehicle: structural excitation sources and acoustical cavity modes. The vibrations caused by acoustical cavity modes inside the tyre are guided through the rim towards the spindle of the car body, resulting in structure borne interior noise and vibrations.

The contact of the tyre with the road causes wave excitations inside the tyre-rim cavity. These acoustical waves travel in both positive and negative circumferential direction, and are called the forward and backward travelling wave, respectively. A standing wave pattern is formed when the wavelength exactly matches the cavity circumference. This is the so-called first acoustical cavity resonance mode and lies between 180 and 250Hz for a passenger car tyre, dependent on both the tyre size as well as the tyre rotational speed.

Sound absorbing devices or noise dampers made of a spongy material disposed inside the tyre cavity to reduce cavity noise and as a consequence interior noise have been developed. US 2019160890A1 describes a pneumatic tyre having a belt-shaped sound-absorbing member bonded via an adhesive layer to the tyre inner surface in a region corresponding to the tread portion along the tyre circumferential direction that has a width of 70% to 95% of a ground contact width of the tyre.

US 20160297261 A1 describes a pneumatic tyre having a tread portion extending in the tyre circumferential direction having land portions defined between adjacent circumferential grooves of the tread portion, the tyre having first and second sound absorbing members adhered to the tyre inner surface of the tread portion which have a total volume of 10 % to 40 % of a capacity of the tyre cavity and are separated from each other by 60 % or more of the width of a center land portion.

EP 1876038 B2 describes an assembly of pneumatic tyre and rim, where a noise damper made of a spongy material is fixed to the inner surface of the pneumatic tyre at a tread region and extends in the tyre circumferential direction. The noise damper has a height of 30 mm or less from the inner surface, and the spongy material has a specific gravity of 0.014 to 0.05, a hardness of 10 to 250 N, and a tensile strength of 70 kPa or more. The noise damper is fixed to the inner surface by an adhesive layer such as an adhesive tape.

US 7182114 B2 describes a tire noise reducing system comprising a pneumatic tire, a wheel rim on which the pneumatic tire is mounted, and a noise damper disposed in a cavity surrounded by an inner surface of the rim and an inner surface of the tire mounted thereon. The noise damper has a volume V2 which is from 0.4 to 20% of the volume V1 of the cavity and is made of a porous material having a hardness of from 10 to 80 N, a tensile strength of not less than 70 kPa and a specific gravity of from 0.014 to 0.026. A tapered portion is formed on at least one of the ends of the noise damper in the circumferential direction of the tire. In the example, the height of the tapered portion in the radial direction of the tire is gradually reduced toward its end, with a preferred angle 0 formed between the bottom surface and the inclined surface of the tapered portion in a range of from 15 to 70°. The noise damper is fixed to the tire cavity by an adhesive or a double-sided tape. The tapered portion enables a mass reduced of the end of the noise damper. Therefore, the stress acting on the adhesion surface of the end is made small so that the cracking damage is more reliably prevented.

Also US 7975740 B2 describes reducing road noise by disposing a noise damper made of a spongy material in a cavity of a tire and discloses a pneumatic tire including a tread portion, a pair of sidewall portions radially inwardly extending from both edges of said tread portion, bead portions disposed at radially inner edges of said sidewall portions, and a noise damper made of a spongy material which is fixed to the inner surface of said pneumatic tire in a tread region and extends in the tire circumferential direction, wherein said noise damper has a height of 30 mm or less from said inner surface, and said spongy material of said noise damper has a hardness of 10 to 250 N, a tensile strength of 70 kPa or more and a specific gravity of 0.014 to 0.052, and wherein said noise damper has, at its circumferential both ends, tapered portions in which said height is gradually decreased. The noise damper is suitably fixed to the inner surface, for example, by an adhesive or a pressure sensitive adhesive double-coated tape.

WO 2021/214096 A1 describes a pneumatic tyre comprising a sound absorbing device. The sound absorbing device is made of a spongy material which is adhered to the inner surface of the pneumatic tyre at a tread region and extends in the tyre circumferential direction. The sound absorbing device comprises at least first and second sound absorbing members, which are separated from each other by a distance (S) in the axial tyre direction. The sound absorbing members are adhered to the inner surface of the pneumatic tyre by at least two annular-shaped adhesive beads provided between each first and second sound absorbing member and the inner surface of the tyre, wherein the adhesive beads are arranged spaced apart from each other in the axial direction and extend in the circumferential direction of the tyre. It was found that using liquid glue for adhering the spongy sound absorbing member was not compatible with using tapered end portions.

The present invention has the object to provide a sound absorbing device capable of reducing the low frequency interior noise between 180 to 250Hz, while ensuring satisfactory endurance performance of the sound absorbing device.

This object is achieved by a vehicle tyre comprising a sound absorbing device according to claim 1.

Advantageous embodiments are the subject of the dependent claims. They may be combined freely unless the context clearly indicates otherwise.

Accordingly, a vehicle tyre is provided, the pneumatic tyre comprising: an inner surface, a tread portion, a pair of sidewall portions radially inwardly extending from both edges of the tread portion, and bead portions disposed at radially inner edges of the sidewall portions, and a sound absorbing device made of a spongy material which is adhered to the inner surface of the pneumatic tyre at a tread region and extends in the tyre circumferential direction, wherein the sound absorbing device comprises at least one sound absorbing member with circumferential outer ends, wherein at least one of the circumferential outer ends comprises at least one step, cut-out, recess, or combinations thereof.

The sound absorbing member is made of a spongy material, such as an open cell foam, and comprises at least one of its circumferential outer ends at least one step, cut-out, recess, or combinations thereof.

Such reduction of the mass at the ends of the sound absorbing member was found to provide an improvement in endurance performance or durability of the foam material which is adhered to the inner surface of the pneumatic tyre using an adhesive. Mass reduction in form of a step, cut-out, or recess at the ends of the sound absorbing foam was found to prevent or at least substantially delay the beginning of delamination at the ends of the foam. Further, a step, cut-out, recess, or combination thereof is easy to manufacture. A step, cut-out, recess, or combination thereof can further be cut with precision into the ends of a small foam body.

The at least one sound absorbing member preferably is shaped in a substantially annular form. In embodiments, the sound absorbing member has a rectangular cross section having a height (Hs) in the radial direction from the inner surface, a width (Ws) in the axial direction and a length (Ls) in the circumferential direction thereby defining for each member circumferential outer ends.

The step, cut-out, recess, or combinations thereof reduced the mass at the end portions of sound absorbing member. Preferably, the step, cut-out, recess, or combinations thereof cut into the sound absorbing member preferably has a certain distance of to the inner surface of the pneumatic tyre and thus has a bottom portion below the cut-out structure. Particularly a step or cut-out provides a bottom portion below the cut-out structure. In embodiments, the height (Hb) of a bottom portion of the step, cut-out, recess, or combinations thereof at the at least one of the circumferential outer ends, preferably equally on both circumferential outer ends, is in a range of 25 % < Hb < 75 %, based on 100% total height of the sound absorbing member. Such a bottom portion stabilises the sound absorbing member against the centrifugal forces that cause delamination between foam body and adhesive glue and reduces the delamination. Particularly, such a height of the bottom portion provided improved prevention of a separation of the sound absorbing member during endurance testing and high-speed testing. Further, a bottom portion facilitates adhesion of the terminal ends of the sound absorbing member.

Generally, steps, cut-outs, recesses or combinations thereof provide for an easy to manufacture cut-out for mass reduction at the the circumferential outer end portions of a sound absorbing member. In preferred embodiments, the cut-out 1s in form of a step. À step provides the easiest to manufacture form of a cut out, where adjustments in form and volume can be implemented without major alterations of the cutting machinery. In preferred embodiments of the step, the height (Hb) of a bottom portion of the step at the at least one of the circumferential outer ends is in a range of 25 % < Hb < 75 5%, based on 100% total height of the sound absorbing member. Preferably, the axial width W of the step corresponds to the axial width Ws of the sound absorbing member. In embodiments, the length L of the step is in a range of from 20 mm < L < 60 mm, preferably in a range of from 30 mm <L < 35 mm.

Preferably, the cut-out is in form of a through-hole in axial direction of the sound absorbing member or the tyre. In embodiments, the through-hole in axial direction is formed as a cut-out in axial direction on at least one of the circumferential outer ends, preferably equally on both circumferential outer ends.

In embodiments, at least one cut-out is formed on at least one circumferential outer end of the sound absorbing member. In preferred embodiments, a cut-out is formed on one or both circumferential outer ends of the sound absorbing member. In embodiments, the cut-out formed in axial direction on at least one of the circumferential outer ends has a round, rectangular, square, elliptical, or rounded polygonal cross-section in axial direction. Such cut-outs can be cut into foam bodies with good precision and reproducibility, which ensures for a balanced mass reduction at both ends.

In preferred embodiments, the cut-out is a cylindrical cut-out. In embodiments, the height (Hb) of foam below the cut-out, measured from an adhesion layer to the cut-out, is about the same height as the height of the foam above the cut-out, measured from the free surface to the cut-out. In other words, the bottom portion below the cut-out preferably has the same height (Hb) than the upper foam portion above the cut-out. In preferred embodiments, the diameter Dh of the cut-out is Dh < 0.7 Hs, where Hs is the total height of the foam.

In other embodiments, a recess is formed in the circumferential outer ends of the sound absorbing member. In embodiments, the recess is formed in axial or radial direction on at least one of the circumferential outer ends, preferably equally on both circumferential outer ends. Cutting one or more recesses allows for the mass reduction to be distributed in axial and/or radial direction. Recesses allow for reproducible manufacture of various structures. In embodiments, the recess has the form of an incision in axial or radial direction. In embodiments, the recess has a partial circular or partial elliptic cross-section in axial direction. Also, these recesses can be cut into foam bodies with good precision and reproducibility, which ensures for a balanced mass reduction at both ends.

In embodiments, the mass reduction 1s provided by one step, cut-out, recess, or combinations thereof onat least one of the circumferential outer ends, preferably equally on both circumferential outer ends.

Preferably, in case of a step both outer ends of the sound absorbing member comprise one step. In embodiments where a cut-out or recess is provided, the mass reduction also can be achieved by providing one cut-out or recess. In other embodiments, the at least one circumferential outer end, preferably equally both circumferential outer ends, comprise several such as two or three cut-outs, recesses, or combinations thereof. Such geometries allow for a distributed arrangement of the mass reduction over the end portion of the sound absorbing member. In embodiments where two or three cut-outs or recesses are provided, the cut-outs or recesses may have identical size or volume, or the size or volume of the cut-outs or recesses may be different. In embodiments where two or three cut- outs or recesses have different size or volume it is preferred that the size or volume increases towards the circumferential end of the sound absorbing member.

At least one outer end of the sound absorbing member comprises a step, a cut-out, a recess, or combinations thereof to allow for a mass reduction at the end portion. In preferred embodiments, both circumferential outer ends of the at least one sound absorbing member comprise a step, a cut-out, a recess, or combinations thereof. Such embodiments provide for more and better-balanced mass reduction.

In embodiments, the volume of removed material by forming steps or cut-outs, such as circles or polygonal slots, or recesses on one or both circumferential outer ends of the sound absorbing member is in a range of from 0.1 vol% to 2 vol%, based on a total volume of the sound absorbing member of 100 vol% calculated without the removed material. In embodiments, where in one circumferential outer end of the sound absorbing member a cut-out is formed the volume reduction is in a range of from 0.05 vol% to 1.5 vol%, preferably in a range of from 0.1 vol% to 1 vol%, based on 100 vol% total foam volume.

In embodiments, the height (Hs) of the at least one sound absorbing member is in a range of 20 mm <

Hs < 60 mm, preferably in a range of 30 mm < Hs < 55 mm, more preferably in a range of 31 mm <

Hs < 40 mm. The height Hs may be for example 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm, 36 mm, 37 mm, 38 mm, 39 mm, 40 mm, 41 mm, 42 mm, 43 mm, 44 mm, or 45 mm. À height of the sound absorbing members in such a range can provide for optimum noise performance. The height Hs is measured in the direction perpendicular to the inner surface with respect to a sound absorbing member fixed to the tyre in the state prior to mounting the tyre on a rim under ordinary temperature and ordinary pressure.

In embodiments, the height (Hb) of the bottom portion of the step at the at least one of the circumferential outer ends is in a range of 7 mm < Hb < 45 mm, preferably in a range of 10 mm < Hb <30 mm, more preferably in a range of 15 mm < Hb < 20 mm. In embodiments, where the height (Hs) of the at least one sound absorbing member is 31 mm, the height (Hb) of the bottom portion of the step may be in a range of 10 mm < Hb < 20 mm, preferably in a range of 15 mm <Hb <20 mm. Such a height (Hb) of the bottom portion provided improved prevention of a separation of the sound absorbing member during endurance testing and high-speed testing. The height Hb is measured in the direction perpendicular to the inner surface with respect to a sound absorbing member fixed to the tyre in the state prior to mounting the tyre on a rim under ordinary temperature and ordinary pressure.

In embodiments, where the axial width (Ws) of the at least one sound absorbing members is 50 mm and the height (Hs) of the at least one sound absorbing member is 31 mm or 35 mm, the diameter Dh ofthe cut-out may be in a range of 15 mm < Dh < 20 mm, preferably in a range of 18 mm < Dh < 20 mm.

The sound absorbing device comprises at least one sound absorbing member. In embodiments, the sound absorbing device comprises first and second sound absorbing members. It was found that two sound absorbing members provide for better noise performance compared to a single sound absorbing device. The sound absorbing device in other embodiments may comprise a plurality of sound absorbing members, such as three, four, six, eight or ten sound absorbing members. In embodiments, where a plurality of sound absorbing members is provided, each gap between the ends of the corresponding sound absorbing member may be displaced by a circumferential distance (D) between the gaps of preferably at least 10% of the circumferential extent of the tyre. The displacement D may be used in compensating a possible reduction of uniformity of the vulcanized tyre after vulcanization.

In embodiments, the axial width (Ws) of the at least one sound absorbing members is in a range of 30 mm < Ws <200 mm. A width of the sound absorbing members in such a range can provide for good noise reduction. In embodiments wherein the sound absorbing device comprises first and second sound absorbing members, both sound absorbing members preferably have an axial width Ws in a range of 30 mm < Ws < 80 mm. The width Ws first and second sound absorbing members may be for example 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, or 70 mm. In embodiments wherein the sound absorbing device comprises one sound absorbing members, the sound absorbing members preferably has an axial width Ws in a range of 50 mm < Ws < 200 mm.

In embodiments wherein the sound absorbing device comprises first and second sound absorbing members, the first and second sound absorbing members are separated from each other by a distance (S) in the axial tyre direction. The distance (S) may cover a part of the inner surface corresponding to the central tread portion, particularly at least a part of the surface of a centre rib in the outer tread portion. In embodiments, first and second sound absorbing members are spaced by a distance (S) in the axial tyre direction in a range of 10 mm < S < 50 mm, preferably in a range of 15 mm <S < 40 mm. Keeping the inner side of the tyre at least partially free of sound absorbing foam members results in less heat build-up in this area.

In embodiments, the circumferential outer ends of the at least one sound absorbing member, preferably of first and second sound absorbing members, provide a gap (G) of from 1 % to 5 %, preferably of from 1 % to 2 %, of the circumference of the tyre, based on 100% total circumference. Thus, in these embodiments a sound absorbing member covers 95-99%, preferably 98-99% of the circumference of the tyre. A gap in these dimensions may correspond to a gap (G) of 50 mm or less in the circumferential direction of a passenger tyre and can provide for maintained noise performance with satisfactory endurance performance.

In embodiments, the sound absorbing device has a volume (Vs) in a range of from 10% to 30% of the total volume (Vc) of 100% of the tyre cavity. The volume Vs of the sound absorbing device is an apparent whole volume and denotes a volume defined by the outward form of the sound absorbing device including the pores or cells inside the sound absorbing device. The volume Ve of the tyre cavity is determined with respect to an assembly in the normal state where a normal internal pressure and no load are applied to the assembly, based on the cross-sectional area of the cavity, the maximum outer diameter of the cavity, the diameter of the rim, and the ratio of the circumference of a circle to its diameter. The sound absorbing device having a volume of from 6% to 18% of the total volume of the tyre cavity provides for good noise performance.

The one or more sound absorbing members are adhered to the inner surface of the pneumatic tyre, preferably by an adhesive component provided between the inner surface of the tyre and the sound absorbing members. The sound absorbing members may be adhered to the inner surface of the pneumatic tyre by any kind of adhesive agent, as long as the foam is fixed firmly and durably to the inner surface. The adhesive component may be based on a pressure-sensitive adhesive. The adhesive component may be or include an adhesive layer or an adhesive strip or adhesive tape. An adhesive strip or adhesive tape may be or include a pressure-sensitive adhesive tape, preferably a double-coated pressure-sensitive adhesive tape. An adhesive layer may based on a silicone adhesive, such as a self- adhesive silicone adhesive composition, a polyurethane adhesive, a synthetic rubber adhesive, or a silanized polyether. Silicone adhesives, polyurethane adhesive, a synthetic rubber adhesives and silanized polyether-based adhesives are commercially available. In embodiments, the adhesive component may comprise an adhesive, preferable an adhesive that is applicable in liquid form, such as a glue. The adhesive component may comprise annular-shaped adhesive beads extending along the inner surface in the circumferential direction of the tyre, preferably extending continuously along the inner surface. Preferred glues are for example glues available under the tradename Loctite® from

Henkel, such as Loctite® SI 5930 FIT. Circumferential outer ends comprise mass reduction in form of at least one step, cut-out, recess, or combinations thereof are particularly useful for adhesion with glue.

The sound absorbing members are made of a spongy material. The term “spongy material” refers to a sponge-like porous material, such as open-cell polyurethane foams. These materials are known to lower the volume of sound by converting vibration energy into heat energy. Examples of the spongy material are a sponge-like porous materials made of a synthetic resin such as an ether-based polyurethane foam, an ester-based polyurethane foam or a polyethylene foam, a foam of a rubber such as a chloroprene rubber foam, an ethylene-propylene rubber foam or a nitrile rubber foam.

Polyurethane foams particularly ether-based polyurethane foams are preferred. The polyurethane foams can be a poly-addition product of isocyanates, polyether/ polyester polyols and water, controlled by catalysts, stabilizers, and other additives, resulting in a cellular polyurethane foam.

In embodiments, the spongy material of the at least one sound absorbing member comprises a polyurethane foam material having: - a specific gravity in a range of from 0.022 to 0.032, or - of from 10 to 25 pores per cm, preferable 15 +/-2 pores per cm, or - a permanent compression set of <10% (measured according to NF EN ISO 1856).

The term “specific gravity” refers the density of a material at a temperature of 20 °C divided by the density of water at that temperature, which is approximately 998 kg/m”.

The polyurethane foam material may have a density of from 20 kg/m? to 30 kg/m’, preferably of from 26 kg/m° to 30 kg/m’ measured according to DIN EN ISO 845. The polyurethane foam material may have a density of 23 +/- 2 kg/m? or of 28 +/- 2 kg/m. The polyurethane foam material comprises cells where the cells may have an average size ranging from 250 um to 400 um with a standard deviation ranging from 20% to 30%. The polyurethane foam material may have a permanent compression set of <10%, preferably of <7% measured according to DIN EN ISO 1856 (22 h, 50 %, 70 °C). Usable polyurethane foam materials are commercially available. Preferred polyurethane foam materials are for example available from Metzeler Schaum GmbH under the tradename Metzonor® MA 3031D, 023 and available from Masterfoam MT28FX. Preferred are open-cell Metzeler Metzonor® 023 or

Metzonor® MA 3031D foams with a density of 23 +/- 2 kg/m? or 28 +/- 2 kg/m°, respectively. These foams provide for optimum noise performance.

A further aspect relates to a wheel assembly comprising a pneumatic tyre according to the invention assembled onto a wheel. For the description of the pneumatic tyre and its components reference is made to description of the tyre above.

In the following the invention is explained in detail by examples and with reference to the enclosed drawings showing preferred embodiments of the present invention, wherein each feature can constitute solely or in combination an aspect of the invention.

Inthe drawings:

Fig. 1 schematically shows a wheel assembly according to an embodiment of the invention comprising a pneumatic tyre assembled onto a wheel.

Fig. 2 schematically shows an equator cross-sectional view of a pneumatic tyre according to an embodiment of the invention.

Fig. 3 schematically shows in Fig. 3a to Fig 3m various geometries of step, cut-outs, and recesses according to various embodiments of the invention.

As shown in Fig. 1, a wheel assembly comprises a pneumatic tyre 1 assembled onto a wheel 20. The pneumatic tyre 1 comprises an inner surface 2, a tread portion 3, and a pair of sidewall portions 4 radially inwardly extending from both edges of the tread portion 3. Bead portions 5 are disposed at radially inner edges of the sidewall portions 4. A sound absorbing device 6 made of a spongy material is adhered to the inner surface 2 of the pneumatic tyre | at a tread region and extends in the tyre circumferential direction. The sound absorbing device 6 in the embodiment of Fig. 1 comprises first and second sound absorbing members 7, wherein the sound absorbing members 7 are separated from each other by a distance S in the axial tyre direction. The distance S may be of from 10 mm to 50 mm, such as 15 mm in a passenger tyre. The sound absorbing members 7 have a rectangular cross section having a height Hs in the radial direction from the inner surface 2, a width Ws in the axial direction and a length Ls in the circumferential direction. The height Hs may be 31 mm < Hs < 40 mm. The width Ws may be 30 mm < Ws < 80 mm for a two-part foam embodiment. The sound absorbing members 7 are adhered to the inner surface 2 of the pneumatic tyre 1 by an adhesive component 8.

Fig. 2 illustrates an equator cross-sectional view of a pneumatic tyre according to an embodiment of the invention. The sound absorbing members have a length Ls in the circumferential direction thereby defining circumferential outer ends 7a, 7b. The circumferential outer ends 7a,7b of the sound absorbing members 7 provide a gap G of from 1 % to 5 % of the circumference of the tyre, based on 100% total circumference. When a plurality of sound absorbing members is provided, each gap G between the ends of the corresponding sound absorbing member may be displaced by a circumferential distance D between the gaps of preferably at least 10% of the circumferential extent of the tyre. Both circumferential outer ends 7a, 7b of the sound absorbing members 7 comprise a step (10).

Fig. 3 illustrates various geometries of step 10, cut-outs 11 and recesses 12 according to various embodiments of the invention. Fig. 3a shows schematically a side view of a sound absorbing member 7 comprising a step 10 in the circumferential outer end. The height Hb of the bottom portion 13 of the step 10 1s in a range of 30 % < Hb < 75 %, based on 100% total height of the sound absorbing member 7. In embodiments, where the height Hs of the sound absorbing member 7 is 31 mm, the height Hb of the bottom portion 13 may be 15 mm or 20 mm.

Figures 3b, 3c and 3d show schematically a side view of a sound absorbing member 7 comprising a cut-out 11 formed in axial direction on the circumferential outer end, where the cut-out 11 has a round cross-section in axial direction in Fig. 3b, an elliptical cross-section in Fig. 3c, and a rounded rectangular cross-section in Fig. 3d. In embodiments of Fig. 3b, the diameter Dh of the cut-out is Dh < 0.7 Hs, where Hs is the total height of the foam.

Figures 3e, 3f and 3g show schematically a side view of a sound absorbing member 7 comprising a recess 12. Fig. 3e illustrates a recess 12 that has a partial circular cross-section in axial direction. Fig. 3f illustrates a recess 12 that has a partial elliptic cross-section in axial direction. Fig. 3g illustrates a recess 12 that has a partial circular cross-section in radial direction.

Fig. 3h to Fig. 3m illustrate schematically a side view of a sound absorbing member 7 comprising two or three cut-outs 11 or recesses 12. Figures 3h to 3] show a side view of a sound absorbing member 7 comprising two cut-outs 11, where the cut-outs 11 have a round cross-section in axial direction in Fig. 3h, an elliptical cross-section in axial direction in Fig. 31, and a rounded rectangular cross-section in axial direction in Fig. 3j. Fig. 3k shows a sound absorbing member 7 comprising two recesses 12 having a partial circular cross-section in radial direction. Fig. 31 shows a side view of a sound absorbing member 7 comprising three cut-outs 11, where the cut-outs 11 have a round cross-section in axial direction, and Fig. 3m shows a side view of a sound absorbing member 7 comprising three cut- outs 11, where the cut-outs 11 have an elliptical cross-section in axial direction. The size of the cut- outs increases towards the circumferential end of the sound absorbing member 7.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1: Endurance tests

The endurance test is a destructive indoor test measuring distance to failure. The test speed was 120 km/h. The test was ended at a survival distance of 20,000 km. Measurement was the total kilometers ofrunning on a drum before tyre and/or foam failure.

All endurance tests were performed on prototype 245/40 ZR 18 97Y tyres. Five sets of prototype tyres were built, all sets of 245/40 ZR 18 97Y tyres. All tyre sets were configured as shown in Table 1 having a sound absorbing foam member applied to the inner-liner with a total of about 130 g glue (Loctite® SI 5930 FIT, Henkel). The height Hs of the foam was 31 mm and the width Ws of the foam was 50 mm.

The first inventive sound absorbing member El was provided with a step at the circumferential outer ends having a height Hb of the bottom portion of the step of 10 mm, the second inventive sound absorbing member E2 was provided with a step having a height Hb of the bottom portion of 20 mm, and absorbing member F5 was provided with a step having a height Hb of the bottom portion of 15 mm. The inventive sound absorbing member E3 had a partial elliptical recess, E4 had a round cut-out with a diameter Dh of 15 mm. Two reference tyres 245/40 ZR 18 97Y tyres were built with a sound absorbing device with straight ends. For each geometrical concept El to ES and Refl two tyres were tested.

Table 1: Endurance measurements

Side view (foam) sampio | SSE eu) | nds 20mm form height x X x

El . : © - pass

E2 ss - 50% failed

NSS NAD oo

NT P ass ism foam height ww S

E5 au pass

After a distance of 20,000 km the status of the foam was evaluated. The foam of examples E1 and ES showed no separation of the foam from the inner surface of the tyre. The foam of example E2 failed in one of two tyres but showed no separation in the second. The foams of examples F3, F4 showed localized foam failure but no separation. The foam of the reference tyre was totally loose on both tyres.

Example 2: High speed tests

The high-speed test is a destructive test procedure measuring the total running time before failure of a tyre rotating against a drum as stipulated in the Economic Commission for Europe Regulation 30 (ECE R30), Annex 7 for a Y rated tyre. À Y rated tyre must pass the legal lower limit of 60 minutes running time.

All high-speed tests were performed on prototype 245/40 ZR 18 97Y tyres. Five sets of inventive prototype tyres were built. The tyre sets were configured as shown in Table 2 having a sound absorbing foam member applied to the inner-liner with a total of about 130 g glue (Loctite® SI 5930

FIT, Henkel). The height Hs of the foam was 31 mm and the width Ws of the foam was 50 mm.

Inventive sound absorbing members E1 to E6 were provided with a step at the circumferential outer ends having a height Hb of the bottom portion of 10 mm, or of 20 mm, having a partial elliptical recess, or a round cut-out as discussed in Example 1. Inventive sound absorbing member E6 had a partial circular recess. For each geometrical concept E1 to E6 two tyres were tested in the high-speed tests. Two reference tyres 245/40 ZR 18 97Y tyres were built without sound absorbing device (Ref2).

Table 2 shows the configuration of the prototype tyres and the results of the high-speed test.

Table 2: high speed measurements

Side view (foam)

Co] So 20mm foam height = ; =

E Le Pas 5

NS SAN

- ay P ass 15mm foam height

ES he pass ar > x

After running time, the status of the foam was evaluated. All examples E1 to E6 showed no foam failure. Example E2 showed tread separation, while examples E1, and E3 to E6 showed no tyre failure.

Also, the reference tyres Ref2 showed no tyre failure. The examples E1 to E6 showed that the sound absorbing device also ensures satisfactory high-speed performance.

The results show that the tyres comprising a step, cut-out or recess have demonstrated excellent durability and have passed the ECE R30 qualification test.

Reference signs: 1 tyre 2 tyre inner surface 3 tread portion 4 sidewall portion 5 bead portion 6 sound absorbing device 7 sound absorbing member 7a,7b outer ends of sound absorbing members 8 adhesive component 10 step 11 cut-out 12 recess 13 bottom portion wheel

Hs height of sound absorbing member

Hb height of bottom portion of sound absorbing member

Ws width of sound absorbing member 20 Ls length of sound absorbing member

Dh diameter of cut-out

G gap between circumferential outer ends

Ve volume of tyre cavity

Vs volume of sound absorbing member

S axial spacing of sound absorbing members

D circumferential distance between the gaps G

Claims (15)

Claims

1. A pneumatic tyre (1) comprising: an inner surface (2), a tread portion (3), a pair of sidewall portions (4) radially inwardly extending from both edges of the tread portion (3), and bead portions (5) disposed at radially inner edges of the sidewall portions (4), and a sound absorbing device (6) made of a spongy material which is adhered to the inner surface (2) of the pneumatic tyre (1) at a tread region and extends in the tyre circumferential direction, wherein the sound absorbing device (6) comprises at least one sound absorbing member (7) with circumferential outer ends (7a, 7b), characterized in that at least one of the circumferential outer ends (7a, 7b) comprises at least one step (10), cut-out (11), recess (12), or combinations thereof.

2. The tyre according to claim 1, wherein the height (Hb) of the bottom portion (13) of the step (10), cut-out (11), recess (12) or combinations thereof at the at least one of the circumferential outer ends (7a, 7b) is in a range of 25 % <Hb < 75 %, based on 100% total height of the sound absorbing member (7).

3. The tyre according to claim 1, wherein the cut-out (11) is formed in axial direction on at least one of the circumferential outer ends (7a, 7b) and has a round, rectangular, square, elliptical, or rounded polygonal cross-section in axial direction.

4. The tyre according to of claim 1, wherein the recess (12) is formed in axial or radial direction on at least one of the circumferential outer ends (7a, 7b).

5. The tyre according to claim 4, wherein the recess (12) has partial circular or partial elliptic cross-section in axial direction.

6. The tyre according to any one of claims 1 or 3 to 5, wherein the at least one circumferential outer end (7a, 7b) comprises two or three cut-outs (11), recesses (12) or combinations thereof.

7. The tyre according to any one of claims 1 to 6, wherein both circumferential outer ends (7a, 7b) of the at least one sound absorbing member (7) comprise a step (10), a cut-out (11), a recess (12) or combinations thereof.

8 The tyre according to any one of claims 1 to 7, wherein the height (Hs) of the at least one sound absorbing member (7) is in a range of 20 mm < Hs < 60 mm, preferably in a range of 30 mm < Hs < 55 mm, more preferably in a range of 31 mm < Hs < 40 mm.

9. The tyre according to any one of claims 1 to 8, wherein the height (Hb) of the bottom portion (13) of the step (10) at the at least one of the circumferential outer ends (7a, 7b) is in a range of 7mm < Hb < 45 mm.

10. The tyre according to any one of claims 1 to 9, wherein the axial width (W) of the at least one sound absorbing members (7) is in a range of 30 mm < Ws < 200 mm, preferably in a range of 30 mm < Ws < 80 mm or in a range of 50 mm < Ws < 200 mm.

11. The tyre according to any one of claims 1 to 10, wherein the sound absorbing device (6) comprises first and second sound absorbing members (7), wherein the first and second sound absorbing members (7) are separated from each other by a distance (S) in the axial tyre direction in a range of 10 mm < S <50 mm.

12. The tyre according to any one of claims 1 to 11, the circumferential outer ends (7a, 7b) of the at least one sound absorbing member (7) provide a gap (G) of from 1 % to 5 % of the circumference of the tyre, based on 100% total circumference.

13. The tyre according to any one of claims 1 to 12, wherein the sound absorbing device (6) has a volume (Vs) in a range of from 10% to 30% of the total volume (Vc) of the tyre cavity.

14. The tyre according to any one of claims 1 to 13, wherein the spongy material of the at least one sound absorbing member (7) comprises a polyurethane foam material having: - a specific gravity in a range of from 0.022 to 0.032, or - of from 10 to 25 pores per cm, preferable 15 +/-2 pores per cm, or

- a permanent compression set of <10% (measured according to NF EN ISO 1856).

15. A wheel assembly comprising a pneumatic tyre (1) assembled onto a wheel (20), characterized in that the tyre (1) is a tyre according to one of claims 1 to 14.