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Pneumatic tire

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20140138002 patent thumbnailZoom

Pneumatic tire


Provided is a pneumatic tire having at least one carcass layer as a skeleton extending in toroidal shape over a pair of bead portions, at least one belt layer and a tread disposed on an outer side in the radial direction of a crown portion of the carcass. In a tire section in the widthwise direction in state where the tire is assembled to an application rim, ratio BD/BW of radius difference BD between radius at a center portion and radius at an end portion in the widthwise direction of an innermost layer of the belt layer, to width BW of the innermost layer, ranges from 0.01 to 0.04, and ratio TD/TW of radius difference TD between radius at a center portion and radius at an end portion of the tread in the widthwise direction of a tread ground surface, to tread ground-contact width TW, satisfies BD/BW<TD/TW.
Related Terms: Crown Pneuma Skeleton Radial Direction

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USPTO Applicaton #: #20140138002 - Class: 152454 (USPTO) -
Resilient Tires And Wheels > Tires, Resilient >Pneumatic Tire Or Inner Tube >Tire Characterized By The Dimension Or Profile Of The Cross Sectional Shape



Inventors: Shinsaku Katayama

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The Patent Description & Claims data below is from USPTO Patent Application 20140138002, Pneumatic tire.

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CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Japanese Patent Application No. 2011-136674 filed Jun. 20, 2011, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a pneumatic tire that has low rolling resistance, good partial wear resistance performance, and reduced weight.

BACKGROUND ART

Recently, in order to address environmental problems such as global warming, products having less of an adverse impact on the environment are being actively developed. Tires are no exception to such products. In case of tires, in order to address the environmental problems, it is important to ensure tire performance that would contribute to higher fuel efficiency of vehicles. As one method to achieve the above task, reducing tire rolling resistance and tire weight has been proposed, and various technologies have been developed until now.

Some of the conventional improvement methods for reducing tire rolling resistance are as follows.

To start with, it is known that a large portion of tire rolling resistance is generated in rubber of a tread portion. As a method for directly addressing the problem, it is effective to replace the rubber for use in the tread portion with rubber with a smaller loss tangent. However, the above method is also known to sacrifice other performance of tires such as wear resistance performance. As another method, it may be easily conceived to reduce a tread thickness so as to reduce rubber, that is to say, the origin of rolling resistance. However, the above method poses a problem that a sufficient wear-resisting period of the tires may not be ensured.

Patent Literature 1 proposes reducing rolling resistance by regulating a shape of a section of a tire. Although the proposed method indeed makes it possible to reduce rolling resistance, when compatibility with other performance, in particular with good wear resistance performance, is considered, a more meticulous tire design is required.

Although Patent Literature 2 discloses reduction in rolling resistance and improvement of wear resistance performance by the more meticulous design of a tire shape, the tire needs to be designed even more meticulously when the weight of the tire is to be reduced.

CITATION LIST Patent Literature

PL1: JP2006327502A PL2: JP2009166819A

SUMMARY

OF INVENTION Technical Problem

In view of the above, the present invention is to propose details of a tire shape for achieving a pneumatic tire that has low rolling resistance, good partial wear resistance performance, and reduced weight.

The present inventor has found that performance of a tire can be improved as desired by meticulously regulating the tire shape and that it is effective to individually regulate respective shapes of reinforcing members as a skeleton of the tire because the shapes of the reinforcing members have significant influence on tire performance. Specifically, the inventor of the present invention has found that, by suppressing shear deformation of a tire in a section in a tire width direction, particularly shear deformation in a tread on an outer side in the widthwise direction thereof, improvement is achieved simultaneously in reduction in rolling resistance resulting from energy loss caused by the deformation and in reduction of wear often generated by shearing force and slip also caused by the deformation.

Furthermore, in the present invention, the present inventor has regulated the shapes of the reinforcing members and then studied the shape of an optimal tire outer surface when the tire is combined with the shapes of the reinforcing members. Then, the present inventor has found that wear resistance performance is ensured even when the tread thickness is reduced, although conventionally it was not possible to reduce the tread thickness. Thus, the present inventor has found that three types of performance, i.e., reduction in rolling resistance, improvement of partial wear resistance performance, and reduction in weight, are simultaneously satisfied, thereby completing the present invention.

Solution to Problem

Primary features of the present invention are as follows.

(1) A pneumatic tire having at least one carcass layer as a skeleton extending in a toroidal shape over a pair of bead portions, at least one belt layer and a tread that are disposed on an outer side in a tire radial direction of a crown portion of the carcass layer, wherein

in a section of the tire in a tire widthwise direction in a state where the tire is assembled to an application rim,

a ratio BD/BW of radius difference BD between radius at a center portion and radius at an end portion in the tire widthwise direction of an innermost layer of the belt layer, to a width BW of the innermost layer, is in the range of 0.01 to 0.04, and

a ratio TD/TW of radius difference TD between radius at a center portion and radius at an end portion of the tread in the tire widthwise direction of a tread ground surface, to a tread ground-contact width TW, satisfies the relation BD/BW<TD/TW.

(2) The pneumatic tire according to the above item (1), wherein

a ratio TGh/TGc of a tread gauge TGh measured in a tread end portion, to a tread gauge TGc measured in a tread center portion, is in the range of 0.5 to 0.9, and

a ratio TGe/TGc of a tread gauge TGe measured in the end portion in the tire widthwise direction of the innermost layer to a tread gauge TGc measured in the tread center portion is in the range of 0.2 to 0.6.

(3) The pneumatic tire according to the above item (1) or (2), wherein a ratio CSWh/CSH of a shortest distance CSWh between a line drawn in parallel with a rotation axis of the tire at a maximum width position of the carcass and a line drawn in parallel with the rotation axis of the tire at a bead toe, to a distance CSH in the tire radial direction between an outermost side of the carcass in the tire radial direction and the bead toe, is in the range of 0.6 to 0.9. (4) The pneumatic tire according to any one of the above items (1)-(3), wherein

A ratio SWh/SH of a shortest distance SWh between a line drawn in parallel with the rotation axis of the tire at a maximum width position of the tire and a line drawn in parallel with the rotation axis of the tire at the bead toe, to a sectional height SH of the tire, is in the range of 0.5 to 0.8.

(5) The pneumatic tire according to any one of the above items (1)-(4), wherein

a ratio BW/CSW of the width BW of the innermost layer, to a maximum width CSW of the carcass, is in the range of 0.8 to 0.94.

(6) The pneumatic tire according to the above items (1)-(5), wherein

a ratio CSL/CSP of a path length CSL from a position corresponding to the end portion in the tire widthwise direction of the innermost layer to a position corresponding to the maximum width position of the carcass, to a path length CSP from a position corresponding to the center portion in the tire widthwise direction of the innermost layer to a position right below a bead core, is in the range of 0.1 to 0.25.

(7) The pneumatic tire according to any one of the above items (1)-(6), wherein

a shortest distance CSEh between a terminal end of a turn-up portion of at least one carcass ply layer and a line drawn in parallel with the rotation axis of the tire at the bead toe is greater than the shortest distance SWh.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be further described below with reference to the accompanying drawings, wherein:

FIG. 1 is a view illustrating a section in a widthwise direction of a pneumatic tire according to the present invention;

FIG. 2A is a view illustrating behaviors before and after application of load to a conventional pneumatic tire, and FIG. 2B is a view illustrating behaviors before and after application of load to a pneumatic tire according to the present invention;

FIG. 3 is a view illustrating how a tread gauge is measured;

FIGS. 4A and 4B are views illustrating tensile strain when a neutral axis of bending is changed;

FIGS. 5A-5E are views illustrating examples of different belt structures of a pneumatic tire according to the present invention;

FIG. 6 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio BD/BW;

FIG. 7 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio TGh/TGc;

FIG. 8 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio TGe/TGc;

FIG. 9 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio CSWh/CSH;

FIG. 10 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio SWh/SH;

FIG. 11 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio BW/CSW; and

FIG. 12 is a graph illustrating rolling resistance performance and wear performance with respect to a ratio CSL/CSP.

DESCRIPTION OF EMBODIMENTS

The following describes a pneumatic tire according to the present invention in detail with reference to the drawings.

FIG. 1 illustrates a section of a pneumatic tire (which may be referred to below as a tire) according to the present invention in a widthwise direction thereof. A tire 10 according to the present invention includes: a carcass 2 as a skeleton, having at least one carcass ply layer (one carcass ply layer in the illustrated example) that extends toroidally between bead portions each embedded with one of a pair of bead cores 1 and that is turned up along each of the bead cores 1 from an inner side to an outer side in the tire widthwise direction; a belt disposed on the outer side in a radial direction of a crown portion of the carcass 2, the belt having at least one slant belt layer (two slant layers 3a and 3b in the illustrated example) formed by coating a number of cords extending in a direction inclined with respect to an equatorial plane CL of the tire with rubber and one circumferential belt layer 4 formed by coating a number of cords extending along the equatorial plane CL of the tire with rubber; and a tread 6 disposed on the outer side in the radial direction of the belt.

The tire 10 as described above is assembled to an application rim 7 and served for use. In the present embodiment, a ratio BD/BW of a radius difference BD between radius at a center portion (the tire equatorial plane CL) and radius at an end portion 3aE in the widthwise direction of the innermost layer 3a among the slant belt layers 3a and 3b and the circumferential belt layer 4, to a width BW of the innermost layer 3a, is in the range of 0.01 to 0.04, in a section in the tire widthwise direction in a state where the tire 10 is assembled to the application rim 7.

Note that it is preferable that the radius difference of the innermost layer 3a in the tire radial direction gradually decreases from the center portion (the tire equatorial plane CL) to the end portion 3aE in the widthwise direction.

A ratio TD/TW of a radius difference TD between a radius at the center portion (the tire equatorial plane CL) and a tread end portion TE of a tread ground surface, to a tread ground-contact width TW, satisfies the relation BD/BW<TD/TW.

It is preferable that the radius difference of a tread surface in the tire radial direction gradually decreases from the center portion in the widthwise direction (the tire equatorial plane CL) to the tread end portion TE of the tread ground surface.

The state where the tire 10 is assembled to the application rim 7 refers to a state where the tire 10 is assembled to a standard rim specified by JATMA and the tire is not filled with an internal pressure or filled with an extremely low internal pressure of up to approximately 30 kPa.

The tread ground-contact width TW refers to a width of the ground contact surface of the tread that comes into contact with a road surface when the tire 10 is pressed against the road surface (e.g. a smooth road surface such as a steel road surface) at the specified internal pressure and at load of 80% in the state where the tire 10 is assembled to the standard rim specified by the JATMA.

Note that, when the TRA and the ETRTO standard are applied in regions where tire is manufactured and used, these standards are to be complied with.

The radius differences BD and TD are measured in a direction parallel to the tire equatorial plane CL.

Although in the description herein the radius difference BD and the width BW are defined by a dimension of the innermost layer, the innermost layer refers to a layer positioned radially innermost among belt layers having a width greater than or equal to 90% of the tread ground-contact width TW. That is to say, even when a belt layer having a width less than 90% of the tread ground-contact width TW is positioned radially innermost, this belt layer is not regarded as the innermost layer defined in the present invention. From the viewpoint of usability and specification of the tread gauge described below, it is preferable that the relation TW≦BW is satisfied, and it is more preferable that the relation 1.1 BW/TW 1.6 is satisfied.

The restriction that the BD/BW is in the range of 0.01 to 0.04 means that the radius difference of the slant belt layer 3a in the width direction thereof is small. In other words, the restriction means that the belt is nearly flat.

As described above, rolling resistance is primarily due to energy loss occurring in rubber of the tread portion, and it is effective to suppress shear deformation, the shear deformation being one example of relevant deformation, in the section in the width direction in order to reduce rolling resistance. Shear deformation described above occurs due to deformation before and after application of load by which the belt which was curved in the ground-contact area is extended flat, as indicated in FIG. 2A (refer to arrows) by a solid line representing a no-load state before a radial tire (with the ratio BD/BW=0.050) having a normal sectional shape of the size 195/65 R15 is filled with the internal pressure and by a broken line representing a loaded state where the radial tire has been filled with an internal pressure of 210 kPa and then applied with load of 4.41 kN. As illustrated in FIG. 2A, a normal radial tire has a radius difference due to a smaller radius in a shoulder portion relative to that in a tread center portion, a portion of the belt that is located near the shoulder portion is stretched in the tire circumferential direction.

As a result, the slant belt layer in which cords are disposed crisscross are deformed like a pantograph to be extended in the circumferential direction, and accordingly, shrink in the width direction. Consequently, the aforementioned shear deformation is promoted, resulting in an increase in hysteresis loss of the tread rubber.

The easiest way to prevent the deformation, in terms of the tire shape, is to design the belt as flat as possible. For example, assume a tire having the same size as the tire illustrated in FIG. 2A in which the belt is flat (with the ratio BD/BW=0.026) and assume the deformation before and after application of load under the same condition as the example illustrated in FIG. 2A. By setting the ratio BD/BW to be 0.04 or less, as shown in FIG. 2B (refer to arrows), the deformation before and after application of load is limited to an extremely low level. Accordingly, by setting the ratio BD/BW to be 0.04 or less, hysteresis loss of the tread rubber is reduced, and the tire with low rolling resistance is achieved.

In actual tire designing, it is essential to set curvedness of the tire in an appropriate range without making the belt completely flat, in view of a deformation component associated with deformation of a side portion and also in view of a ground-contact configuration and distribution of ground-contact pressure required for prevention of uneven wear. An ardent study on the appropriate range has revealed that the ratio BD/BW is be at least 0.01. With the above structure, shear deformation of the tread rubber is limited, and therefore shearing force and distribution of slip within the contact patch change toward reduction. Thus, the above structure provides an advantageous effect of improving partial wear resistance performance at the same time.

The restriction that the ratio BD/BW and the ratio TD/TW satisfy the relation BD/BW<TD/TW indicates that the belt has the flat shape, while the shape of the crown portion on the tire outer surface has a greater falling ratio than the belt and is curved.

Similarly to the belt shape, in order to obtain an appropriate ground-contact configuration and an appropriate distribution of ground-contact pressure, it is essential to define the shape of the tire outer surface to have an appropriate relation with the belt shape without making the shape of the tire outer surface completely flat. When the tire outer surface has a shape more flat than the belt shape, the tire center portion is off the road surface, and the ground-contact length is greater in the tread end portion TE than in the tire center portion. In this case, rolling resistance is deteriorated, and moreover, the ground-contact pressure in the shoulder portion, which includes the tread end portion TE, is increased, and partial wear resistance performance is badly deteriorated. From the above, by setting the relation BD/BW<TD/TW, rolling resistance performance and partial wear resistance performance are improved.

The ratio restriction BD/BW<TD/TW also means that a tread gauge TGh measured in the tread end portion TE is less than a tread gauge TGc measured in the tread center portion.

Generally speaking, when the tread gauge measured on a shoulder portion side is small despite that the amount of wear is large on the shoulder portion side, the wear-resisting period might not be ensured, and wear resistance performance might be deteriorated. However, when the belt has the flat shape as in the present invention, the shoulder portion with the smaller tread gauge prevents the aforementioned increase in the ground-contact length and in the ground-contact pressure in the shoulder portion. As a result, good wear-resistance is achieved. Furthermore, with the small tread gauge in the shoulder portion, the amount of rubber deformed is reduced. As a result, rolling resistance is further lowered, and moreover, an advantageous effect that the weight of the tire is reduced is achieved.

The present inventor has conducted an ardent study on the appropriate range for the tread gauge and found according to Examples described below that a ratio TGh/TGc of the tread gauge TGh measured in the tread end TE, to the tread gauge TGc measured in the tread center portion, is preferably in the range of 0.5 to 0.9, and a ratio TGe/TGc of the tread gauge TGe measured in the end portion 3aE of the innermost layer 3a in the width direction, to the tread gauge TGc measured in the tread center portion, is preferably in the range of 0.2 to 0.6.

Furthermore, the relation TGe≦TGh is preferably satisfied.

Moreover, the ratio TD/TW is preferably greater than or equal to 0.05, more preferably in the range of 0.05 to 0.15. The reason is that, in the tire with the flat belt line in which the ratio BD/BW is at most 0.04 as in the present invention, when the ratio TD/TW is greater than 0.15, this means, in a case of a normal size tire, that the tread gauge measured in the shoulder portion does not exist.

In addition, it is preferable that the tread gauge gradually decreases from the tread center portion to the shoulder portion.

The tread gauge refers to a thickness of the tread rubber from an outer side of the reinforcing member of the outermost circumferential belt layer 4 among the belts to the tread ground surface as measured on a normal line of the carcass 2 in the section in the tire widthwise direction in the state where the tire 10 is assembled to the application rim 7. In a portion of the tread where the innermost layer 3a is disposed, when a direction of the normal line of the carcass 2 considerably differs from a direction of a normal line of the innermost layer 3a, the tread gauge is measured on the normal line of the innermost layer 3a.

For example, with reference to FIG. 3, the tread gauge TGc in the tread center portion is measured on the tire equatorial plane CL and is identified as the thickness of the tread rubber measured from an outer side of a cord C included in the circumferential belt layer 4 to the tread ground surface. The tread gauge TGh at the tread end portion TE is measured on the normal line L1 of the carcass 2 passing through the tread end portion TE and is identified as the thickness of the tread rubber measured from the outer side of a cord C included in the circumferential belt layer 4 to the tread ground surface. The tread gauge TGe at the end portion 3aE of the innermost layer 3a in the widthwise direction is measured on the normal line L2 of the carcass 2 passing through the end portion 3aE in the widthwise direction and is identified as the thickness of the tread rubber measured from the outer side of a cord C included in the circumferential belt layer 4 to the tread ground surface.



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stats Patent Info
Application #
US 20140138002 A1
Publish Date
05/22/2014
Document #
14127279
File Date
05/17/2012
USPTO Class
152454
Other USPTO Classes
International Class
60C3/04
Drawings
8


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Resilient Tires And Wheels   Tires, Resilient   Pneumatic Tire Or Inner Tube   Tire Characterized By The Dimension Or Profile Of The Cross Sectional Shape