TECHNICAL FIELD

The present technology relates to a pneumatic tire comprising a belt-shaped sound-absorbing member bonded to a tire inner surface in a region corresponding to a tread portion, and, more specifically, to a pneumatic tire allowing for ensured satisfactory wet performance and reduced air column resonance caused by circumferential grooves.

BACKGROUND ART

In pneumatic tires, cavernous resonance caused by the vibration of air that the tire is filled with is one cause of noise being generated. When a tire is rolled, uneven road surfaces cause a tread portion to vibrate. The vibrations of the tread portion cause the air inside the tire to vibrate which causes cavernous resonance to be generated.

One proposed method for reducing the noise produced by this phenomenon of cavernous resonance is to provide a sound-absorbing member within the cavity formed between the tire and the rim of the wheel. More specifically, a belt-shaped sound-absorbing member is bonded to the tire inner surface in a region corresponding to the tread portion (see, for example, Japanese Unexamined Patent Application Publication Nos. 2002-67608A and 2005-138760A).

Meanwhile, circumferential grooves that extend in the tire circumferential direction are formed in the tread portion of a pneumatic tire; such circumferential grooves are one factor that causes the production of air column resonance, which has a frequency (approximately 800 Hz to 1.5 kHz) higher than that of cavernous resonance (approximately 200 Hz to 250 Hz). In particular, increasing the width of the circumferential grooves in order to improve wet performance also increases the air column resonance produced thereby. Reducing the width of the circumferential grooves in order to reduce air column resonance leads to reduced wet performance. There is therefore a demand for reduced air column resonance caused by circumferential grooves while ensuring satisfactory wet performance.

SUMMARY

The present technology provides a pneumatic tire that allows for ensured satisfactory wet performance and reduced air column resonance caused by circumferential grooves.

A pneumatic tire according to the present technology is a pneumatic tire provided with an annular-shaped tread portion extending in a tire circumferential direction, a pair of side wall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the inner side in the tire radial direction of the side wall portions, a plurality of circumferential grooves that extend in the tire circumferential direction being provided in the tread portion, and a belt-shaped sound-absorbing member being bonded via an adhesive layer to a tire inner surface in a region corresponding to the tread portion along the tire circumferential direction, the tire being characterized in that the sound-absorbing member has a width of 70% to 95% of a ground contact width of the tire, and the circumferential grooves included in the region in the tire width direction in which the sound-absorbing member is disposed have a total width of 25% to 40% of the width of the sound-absorbing member.

The inventors discovered that sound-absorbing member and an adhesive layer used to bond the same provided on a tire inner surface in order to reduce cavernous resonance also contribute in reducing air column resonance caused by the circumferential grooves formed in the tread portion, and arrived at the present invention.

Specifically, the present technology provides a pneumatic tire comprising a belt-shaped sound-absorbing member bonded via an adhesive layer to a tire inner surface in a region corresponding to the tread portion along the tire circumferential direction, wherein the width of the sound-absorbing member is from 70% to 95% of the tire ground contact width, and the total width of the circumferential grooves included in the region in which the sound-absorbing member is disposed in the tire width direction is from 25% to 40% of the width of the sound-absorbing member, thereby making it possible to suppress air column resonance noise caused by the circumferential grooves from being transmitted to the interior of the cavity within the pneumatic tire and resonating, thereby reducing air column resonance noise, while ensuring satisfactory wet performance.

In the present technology, the tire ground contact width is the ground contact width in the tire axial direction as measured when the tire is mounted on a regular rim and inflated to a regular internal pressure, and placed vertically upon a flat surface with a regular load applied thereto. A “regular rim” is a rim defined by a standard for each tire according to a system of standards that includes standards on which tires are based, and refers to a “standard rim” in the case of JATMA, refers to a “design rim” in the case of TRA, and refers to a “measuring rim” in the case of ETRTO. If the tire is a tire for installation on a new vehicle, the genuine wheel upon which the tire is mounted is used. “Regular internal pressure” is the air pressure defined by standards for each tire according to a system of standards that includes standards on which tires are based, and refers to “maximum air pressure” in the case of JATMA, to the maximum value in the table of “TIRE ROAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, and to “inflation pressure” in the case of ETRTO. In the case of a tire for installation upon a new vehicle, the air pressure displayed on the vehicle is used. “Regular load” is the load defined by standards for each tire according to a system of standards that includes standards on which tires are based, and refers to “maximum load capacity” in the case of JATMA, to the maximum value in the table of “TIRE ROAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, and to “LOAD CAPACITY” in the case of ETRTO. If the tire is for use with a passenger vehicle, a load corresponding to 88% of the loads described above is used. If the tire is a tire for installation on a new vehicle, a wheel load calculated by dividing the front and rear axle loads listed on the vehicle inspection certification by two is used.

The width of the circumferential grooves is the width of the grooves in the road contact surface of the tread portion as measured when the tire is mounted on a regular rim and inflated to a regular internal pressure. However, because circumferential grooves having a width of 1.8 mm or less have little effect upon air column resonance, the width of these circumferential grooves is excluded from the total width of the circumferential grooves included in the region in the tire width direction in which the sound-absorbing member is disposed.

The sound-absorbing member is preferably disposed so that all of the circumferential grooves formed in the tread portion are included within the region in the tire width direction in which the sound-absorbing member is disposed. This allows for the effective reduction of air column resonance caused by the circumferential grooves.

The adhesive layer is preferably double-sided adhesive tape having a thickness of 0.1 mm to 1.2 mm. This allows for the effective reduction of air column resonance caused by the circumferential grooves.

It is preferable that the pneumatic tire of the present technology have a tire ground contact width of 110 mm to 170 mm, and the circumferential grooves disposed in the region in the tire width direction in which the sound-absorbing member is disposed include four main grooves having a width of at least 4 mm. This allows for effective reduction of air column resonance caused by the circumferential grooves while maintaining satisfactory wet performance in a pneumatic tire having a tire ground contact width as described above.

It is preferable that the pneumatic tire of the present technology have a tire ground contact width of 150 mm to 280 mm, and the circumferential grooves disposed in the region in the tire width direction in which the sound-absorbing member is disposed include three main grooves having a width of at least 10 mm and one or two auxiliary grooves having a width of less than 10 mm. This allows for effective reduction of air column resonance caused by the circumferential grooves while maintaining satisfactory wet performance in a pneumatic tire having a tire ground contact width as described above.

The widest circumferential groove out of the circumferential grooves disposed in the region in the tire width direction in which the sound-absorbing member is disposed preferably has a width of at least 15 mm. Forming a circumferential groove having a width of at least 15 mm in the tread portion in this manner allows for enhanced wet performance.

Because the sound-absorbing member is imparted with a comparatively large width in the present technology, shear strain readily occurs in the bonded surface of the sound-absorbing member as the result of deformation of the tread portion. It is therefore necessary to ensure that the sound-absorbing member remains satisfactorily bonded to the tire inner surface. One preferable method of accomplishing this is to dispose the ends in the tire width direction of the sound-absorbing member in regions outside the areas directly beneath the circumferential grooves. Specifically, when a tire changer is used to remove the pneumatic tire from the wheel, the tread portion exhibits pronounced bending at the circumferential grooves; thus, if the ends in the tire width direction of the sound-absorbing member are present in areas directly beneath the circumferential grooves, there is a risk of the ends of the sound-absorbing member debonding from the tire inner surface when deformation of the tread portion occurs. By contrast, disposing the ends in the tire width direction of the sound-absorbing member in regions outside the areas directly beneath the circumferential grooves allows the occurrence of such debonding of the sound-absorbing member to be avoided.

It is preferable that the sound-absorbing member be constituted by a single sound-absorbing member extending in the tire circumferential direction, the member being of uniform thickness at least within a range corresponding to the bonded surface of the sound-absorbing member as seen in a cross-section orthogonal to the longitudinal direction thereof, and having a constant cross-sectional shape along its longitudinal direction. This allows the volume of sound-absorbing member per unit of bonded area to be maximized, thereby yielding superior noise-reducing effects. In addition, a sound-absorbing member having such a shape is easy to machine, thereby reducing manufacturing costs.

It is preferable that the volume of sound-absorbing member be greater than 20% of the volume of the cavity formed within the tire when the tire is mounted on a rim. Increasing the volume of the sound-absorbing member in this way allows superior noise-reducing effects to be obtained, and allows a satisfactory bonded state to be maintained over long periods of time even when a large sound-absorbing member is used. The term “volume of the cavity” refers to the volume of the cavity formed between the tire and the rim when the tire is mounted on a regular rim and inflated to a regular internal pressure.

It is preferable that the sound-absorbing member have a hardness of 60 N to 170 N, and a tensile strength of 60 kPa to 180 kPa. Sound-absorbing member having these physical properties will exhibit superior resistance to shear strain caused by the swelling of the tire when being inflated or deformation of the tread portion due to contact with the ground. The hardness of the sound-absorbing member is as measured according to Japanese Industrial Standard JIS-K 6400-2, “Flexible cellular polymeric materials—Physical properties—Part 2: Determination of hardness and stress-strain characteristics in compression”, method D (method for calculating force after constant 25% compression for 20 seconds). The tensile strength of the sound-absorbing member is as measured according to JIS-K 6400-5, “Flexible cellular polymeric materials—Physical properties—Part 5: Determination of tensile strength, elongation at break and tear strength”.

It is preferable that the adhesive layer be constituted by double-sided adhesive tape having a peel adhesive force in a range from 8 N/20 mm to 40 N/20 mm. This facilitates the processes of bonding the sound-absorbing member and removing the member when the tire is being disposed of while maintaining satisfactory anchoring strength on the part of the sound-absorbing member. The peel adhesive force of the double-sided adhesive tape is as measured according to JIS-Z 0237. Specifically, a double-sided adhesive sheet is bonded to a piece of PET film having a thickness of 25 μm to create a backing. The adhesive sheet with backing is cut to a 20 mm×20 mm square to create a test sample. The removable liner is peeled off the test sample, and the exposed adhesive surface is bonded to a piece of stainless steel (SUS: B304; surface finish: BA) sheet acting as a substrate using a 2-kg reciprocating roller. This arrangement is kept in a 23° C., 50% relative humidity environment for 30 minutes, after which a tensile tester is used to measure the 180° peel adhesive force of the adhesive sheet to the SUS sheet according to JIS-Z 0237 and in a 23° C., 50% relative humidity environment at testing conditions of 180° peel angle and 300 mm/min strain rate.

If a tire structure in which a carcass layer is mounted between the pair of bead portions, a belt layer is disposed to the outer circumferential side of the carcass layer in the tread portion, the carcass layer is folded back from the tire inner side to the tire outer side around bead cores disposed in each of the bead portions, and the folded back portion of the carcass layer extends to a position overlapping the belt layer is adopted in the present technology, it is preferable that the ends in the tire width direction of the sound-absorbing member be disposed at positions at least 5 mm away from the positions of the ends of the carcass layer. Large amounts of heat are generated near the positions of the ends of the carcass layer in the tire structure described above; thus, separating the ends of the sound-absorbing member from the positions of the ends of the carcass layer allows the durability of the pneumatic tire to be improved.

