JP5902394B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire with reduced rolling resistance.

  In recent years, development in consideration of environmental problems such as global warming has been actively carried out, and one example is the reduction in fuel consumption of automobiles. One means for achieving this is to reduce the rolling resistance of the tire, and various technical developments have been made conventionally.

When a tire rolls under load, bending deformation, shear deformation, and the like occur in a tread portion, a sidewall portion, and the like, and energy loss occurs due to consumption of deformation energy as heat energy. This energy loss is particularly generated in the tread rubber constituting the tread portion, and reducing this leads to an effective reduction of the rolling resistance of the tire. As a direct improvement method, the tread rubber can be changed to one having a small loss tangent (tan δ). However, this method is also known to sacrifice various performances of the tire including the wear resistance. On the other hand, a method of reducing the thickness of the tread part can be easily considered in order to reduce rubber, which is a source of increasing rolling resistance, but in this case, it is a problem that a sufficient life until tire wear cannot be secured. become.
For example, Patent Document 1 proposes reducing the rolling resistance by devising the cross-sectional shape of a tire. With this proposal, it is possible to reduce rolling resistance while ensuring steering stability, wear resistance, durability, and the like.

JP 2006-1360 A

A detailed analysis of the strain energy loss generated in the tread rubber reveals that the strain energy loss due to shear deformation (tire circumferential direction and tire width direction) is dominant, especially at the belt end of the shoulder. It was.
Accordingly, an object of the present invention is to provide a pneumatic tire in which rolling resistance is further reduced while suppressing strain energy loss at the belt end and maintaining various performances of the tire.

The gist of the present invention is as follows.
(1) A carcass extending in a toroidal shape between a pair of bead cores is used as a skeleton, and a belt composed of a plurality of belt layers and a plurality of circumferential grooves extending along the tire equatorial plane are formed outside the carcass in the radial direction. In pneumatic tires with treads,
The tread consists of at least one tread rubber layer,
Among the end portions of the plurality of belt layers, a rubber sheet is disposed between the belt and the tread rubber layer so as to cover an end portion located on the outermost side in the tire width direction,
Loss tangent of the rubber sheet at 60 ° C. is rather low than the loss tangent of the tread rubber layer,
The tire width direction inner side edge part of the rubber sheet is 10 mm or more outside in the tire width direction outside the tire width direction outer side edge part of the outermost circumferential groove in the tire width direction among the plurality of circumferential grooves,
A pneumatic sheet characterized in that an outer end portion in the tire width direction of the rubber sheet is 10 mm or more and 20 mm or less in an outer portion in the tire width direction from an end portion of the plurality of belt layers located on the outermost side in the tire width direction. tire.

(2) The carcass is folded from the carcass main body extending in a toroidal shape between the pair of bead cores around the bead core from the inner side to the outer side in the tire width direction, and the belt and the carcass main body The pneumatic tire according to the above (1), which has a carcass turn-up portion extending between the two.

( 3 ) The tread is composed of a base rubber layer and a cap rubber layer radially outside the base rubber layer,
The loss tangent tan δg of the rubber sheet at 60 ° C., the loss tangent tan δb of the base rubber layer, and the loss tangent tan δc of the cap rubber layer are:
tan δg <tan δb <tan δc
The pneumatic tire according to (1) or (2) , wherein the relationship is satisfied.

It is sectional drawing of the width direction of the tread half part of the pneumatic tire which concerns on 1st Example of this invention. It is sectional drawing of the width direction of the tread half part of the pneumatic tire which concerns on 2nd Example of this invention. It is sectional drawing of the width direction of the tread half part of the pneumatic tire which concerns on 3rd Example of this invention.

Hereinafter, the pneumatic tire of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view in the width direction of a tread half portion of a pneumatic tire according to a first embodiment of the present invention. The pneumatic tire of the present invention has a carcass 2 extending in a toroidal shape between a pair of bead cores as a skeleton, and includes a belt and a tread 6 composed of two inclined belt layers 3a and 3b outside the carcass 2 in the radial direction. Yeah. The carcass 2 has a low turn-up structure in which the end portion of the carcass ply is terminated at the bead portion. The two inclined belt layers 3a and 3b are formed by covering a large number of cords extending in a direction oblique to the tire equatorial plane CL and intersecting each other with rubber. A plurality of circumferential grooves 9 extending along the tire equatorial plane CL are formed in the tread 6.
The tread 6 has a single structure including a cap rubber layer 6C which is a single tread rubber layer.
Further, the outermost inclined belt in the radial direction of the two inclined belt layers 3a and 3b so as to cover the end 3aE located on the outermost side in the tire width direction among the ends of the two inclined belt layers 3a and 3b. The rubber sheet 7 is disposed between the layer 3b and the cap rubber layer 6C. The loss tangent of the rubber sheet 7 at 60 ° C. is lower than the loss tangent of the cap rubber layer 6C.

FIG. 2 is a cross-sectional view in the width direction of the tread half portion of the pneumatic tire according to the second embodiment of the present invention. In the pneumatic tire according to the second embodiment, the same components as those of the pneumatic tire according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
The carcass 2 has a high turn-up structure in which the end of the carcass ply extends to the center of the sidewall.
The tread 6 has a cap / base structure including a base rubber layer 6B and a cap rubber layer 6C on the radially outer side of the base rubber layer 6B.
Further, the outermost inclined belt in the radial direction of the two inclined belt layers 3a and 3b so as to cover the end 3aE located on the outermost side in the tire width direction among the ends of the two inclined belt layers 3a and 3b. A rubber sheet 7 is disposed between the layer 3b and the base rubber layer 6B. The loss tangent of the rubber sheet 7 at 60 ° C. is lower than the loss tangent of the base rubber layer 6B and the loss tangent of the cap rubber layer 6C.

FIG. 3 is a cross-sectional view in the width direction of the tread half portion of the pneumatic tire according to the third embodiment of the present invention. In the pneumatic tire according to the third example, the same components as those of the pneumatic tire according to the first example and the second example are denoted by the same reference numerals, and the description thereof is omitted.
The carcass 2 is folded from the carcass main body portion 2h extending in a toroidal shape between the pair of bead cores, around the bead core from the inner side to the outer side in the tire width direction, and extends between the belt and the carcass main body portion 2h. It is an envelope structure which has the part 2o.
The belt includes two inclined belt layers 3a and 3b and two circumferential belt layers 4a and 4b. The two circumferential belt layers 4a and 4b are made by covering a large number of cords extending along the tire equatorial plane CL with rubber. The circumferential belt layer 4a is disposed across the tire equatorial plane CL so as to cover the ends of the two inclined belt layers 3a and 3b. The circumferential belt layer 4b is disposed only in the shoulder portion, and is interrupted at the tread center portion including the tire equatorial plane CL.
The two inclined belt layers 3a and 3b and the two inclined belt layers 3a and 4bE so as to cover the ends 4aE and 4bE located at the outermost side in the tire width direction among the ends of the two circumferential belt layers 4a and 4b. Among the circumferential belt layers 4a and 4b of 3b and 2b, the rubber sheet 7 is arranged between the circumferential outermost belt layer 4b and the base rubber layer 6B.
In the shoulder portion, cushion rubber 8 is disposed between the inclined belt layer 3a and the carcass folded portion 2o.

Hereinafter, the operation of the present invention will be described.
As described above, changing the loss tangent of the cap rubber layer 6C in contact with the road surface to a small one is not an effective means because wear resistance and the like are sacrificed. Therefore, in the first embodiment, by disposing a rubber sheet 7 having a loss tangent lower than the loss tangent of the cap rubber layer 6C at the position of the belt end of the shoulder portion, distortion energy loss at this position is suppressed and rolling is performed. Reduced resistance.
When the cap / base structure is adopted for the tread 6 as in the second embodiment, generally, the loss tangent (tan δ) of the base rubber layer 6B is set to be smaller than the loss tangent of the cap rubber layer 6C to generate heat. It is suppressed. Therefore, in order to suppress strain energy loss at the belt end of the shoulder portion, it is conceivable to increase the thickness of the rubber at this position, that is, the base rubber layer 6B. Therefore, if the base rubber layer 6B is made thicker throughout the entire tire width direction, the cap rubber layer 6C becomes thinner accordingly, so that the cap rubber layer 6C has the expected performance, for example, wear resistance and durability performance. May worsen. On the other hand, when only the base rubber layer 6B of the shoulder portion is thickened, the contour shape of the tread 6 becomes complicated and the product size varies with it, which may cause various performance deteriorations and product defects.
Therefore, in the present invention, the rubber sheet 7 that is separate from the base rubber layer 6B and has a loss tangent smaller than the loss tangent of the base rubber layer 6B is disposed so as to cover the belt end of the shoulder portion. Can be solved. Moreover, since the process of sticking the rubber sheet 7 is easy, a decrease in productivity can be minimized.
Particularly, in the case of the pneumatic tire according to the third embodiment, since the envelope structure is adopted, the carcass folded portion 2o exists under the belt end where the strain concentrates. For this reason, in a pneumatic tire having an envelope structure, rolling resistance is likely to increase as compared with a pneumatic tire having a high turn-up structure or a low turn-up structure. Therefore, by covering the belt end where the strain energy is most likely to be generated with the rubber sheet 7 having a low loss tangent, the heat generated by the strain can be efficiently suppressed, so that the effect of the present invention is remarkably exhibited.

As shown in FIG. 3, the tire width direction inner end 7IE of the rubber sheet 7 is preferably 10 mm or more on the outer side in the tire width direction from the outer end in the tire width direction of the circumferential groove 9 on the outermost side in the tire width direction. The land portion near the circumferential groove 9 located in the shoulder portion repeatedly undergoes deformation such as compression during tire rolling. Therefore, the rubber sheet 7 is in the vicinity of the circumferential groove 9, that is, the tire width direction inner end portion 7IE of the rubber sheet 7 is less than 10 mm from the tire width direction outer end portion of the outermost circumferential groove 9 in the tire width direction. If it is disposed at the position, the durability may be inferior.
On the other hand, the outer end 7OE in the tire width direction of the rubber sheet 7 is an end located on the outermost side in the tire width direction among the ends of the two inclined belt layers 3a and 3b and the two circumferential belt layers 4a and 4b. 4aE and 4bE are preferably 10 mm or more and 20 mm or less on the outer side in the tire width direction. Since the end portions 4aE and 4bE of the circumferential belt layers 4a and 4b tend to jump outward in the radial direction at the time of molding, this jumping phenomenon occurs when the end portion 7OE is disposed at a position less than 10 mm from the end portions 4aE and 4bE. As a result, workability may decrease and product defects may increase. Further, in the present invention, the rubber sheet 7 is added, so that the side rubber 10 is thinned to maintain the pneumatic tire gauge at the time of product. Therefore, when the end portion 7OE is disposed at a position more than 20 mm from the end portions 4aE and 4bE, a region where the side rubber 10 is thinned is enlarged, and defects are likely to occur at the time of molding, which may reduce workability.
Therefore, in order to reduce rolling resistance while maintaining various performances, the length and arrangement position of the rubber sheet 7 are defined as described above.

The loss tangent tan δg of the rubber sheet 7 at 60 ° C., the loss tangent tan δb of the base rubber layer 6B, and the loss tangent tan δc of the cap rubber layer 6C are:
tan δg <tan δb <tan δc
It is preferable to satisfy this relationship.
When the loss tangent of the rubber is lowered, the heat generation property is lowered, so that the rolling resistance is reduced and the rolling resistance performance is improved. However, it has been found that reducing the loss tangent of rubber also reduces the wet performance. Therefore, the loss tangent tan δc of the cap rubber layer 6C is not changed, and the rubber sheet 7 having the lowest loss tangent is disposed at a position where the distortion is large and the energy loss is large while maintaining the wet performance. Rolling resistance performance can be improved.

  The pneumatic tire of the present invention is not limited to the first to third embodiments described above. For example, the belt can have three inclined belt layers. In FIG. 3, the end portions 4aE and 4bE of the circumferential belt layers 4a and 4b are at the same position in the tire width direction, but may be shifted. Alternatively, the carcass 2 may be composed of two layers of carcass plies, with one layer of carcass ply having a high turn-up structure and the other layer of carcass ply having a low turn-up structure.

Examples of the present invention will be described below, but the present invention is not limited thereto.
Invention example tires, reference example tires, and comparative example tires (all tire sizes: 195 / 65R15) were prototyped and various performances described below were evaluated.

Inventive tires 1-1 to 1-3 and comparative tires 1-1 to 1-3 were measured for rolling resistance depending on the presence or absence of rubber sheet 7.
Invention example tire 1-1 has the structure shown in FIG. 3 and the specifications shown in Table 1.
The comparative example tire 1-1 is the same as the example tire 1-1, except that the rubber sheet 7 is not provided.
Invention Example Tire 1-2 is the same as Invention Example Tire 1-1 except that the carcass 2 has a high turn-up (HTU) structure.
The comparative example tire 1-2 is the same as the inventive example tire 1-2 except that the rubber sheet 7 is not provided.
Invention Example Tire 1-3 is the same as Invention Example Tire 1-1 except that the carcass 2 has a low turn-up (LTU) structure.
Comparative Example Tire 1-3 is the same as Invention Example Tire 1-3 except that it does not have rubber sheet 7.

(Rolling resistance test)
In the rolling resistance test, each test tire was assembled on a standard rim, the internal pressure was adjusted to 210 kPa, and then the rolling resistance of the axle was measured using a drum testing machine (speed: 80 km / h) having a steel plate surface with a diameter of 1.7 m. This was done by seeking power. The rolling resistance was measured according to ISO18164, using a smooth drum and force type. It shows that the smaller the rolling resistance, the better the performance.

From Table 1, it can be seen that the rolling resistance of the invention example tire having the rubber sheet 7 is reduced regardless of the carcass structure.
Further, in the case of the envelope structure, it can be seen that the invention example tire 1-1 having the rubber sheet 7 has a rolling resistance improved by 2.3% as compared with the comparative example tire 1-1 not having the rubber sheet 7. In the case of the high turn-up structure, it can be seen that the invention example tire 1-2 having the rubber sheet 7 has a rolling resistance improved by 1.2% as compared with the comparative example tire 1-2 not having the rubber sheet 7. In the case of the low turn-up structure, it can be seen that the inventive tire 1-3 having the rubber sheet 7 has a rolling resistance improved by 1.2% compared to the comparative tire 1-3 having no rubber sheet 7.

Inventive Example Tire 2-1 and Reference Examples 2-2 to 2-4 were subjected to measurement of the occurrence rate of groove bottom cracks and the occurrence of air under the belt by changing the length and / or arrangement position of the rubber sheet 7. .
Invention Example Tire 2-1 and Reference Examples 2-2 to 2-4 have the structure shown in FIG.
(Confirmation of groove bottom crack occurrence rate and belt under air occurrence rate)
100 tires were manufactured for each invention example tire and reference example tire , each obtained test tire was assembled to a standard rim, the internal pressure was adjusted to 210 kPa, and then mounted on the vehicle, and a running test of 50,000 km. And the occurrence of cracks in the groove bottom of the circumferential groove 9 on the outermost side in the tire width direction was confirmed.
Further, after confirming the occurrence of groove bottom cracks, each test tire was cut along the tire equatorial plane CL, and the occurrence of air under the inclined belt layer 3a was confirmed.
In Table 2, the distance from the groove is the distance from the inner end 7IE in the tire width direction of the rubber sheet 7 from the outer end in the tire width direction of the circumferential groove 9, and the distance from the belt end is the rubber This is the distance of the outer end 7OE in the tire width direction of the seat 7 from the ends 4aE and 4bE of the circumferential belt layers 4a and 4b.

  From Table 2, the tire width direction inner side end portion 7IE of the rubber sheet 7 is 10 mm or more outside the tire width direction outer end portion of the tire circumferential direction groove 9, and the rubber sheet 7 has an outer end portion in the tire width direction. In invention example tire 2-1, in which 7OE is 10 mm or more and 20 mm or less on the outer side in the tire width direction from the end portions 4aE and 4bE of the circumferential belt layers 4a and 4b, the groove bottom crack generation rate and the belt under-air generation rate are both 0%. It turns out that it is.

Invention Example Tires 3-1 and 3-2 and Comparative Example Tires 3-1 to 3-4, the presence or absence of the rubber sheet 7, the rubber sheet 7, the base rubber layer (BASE) 6B, and the cap rubber layer (CAP) 6C The rolling tangent and wet brake performance were measured by changing the loss tangent.
Inventive tires 3-1 and 3-2 and comparative tires 3-1 to 3-4 have the structure shown in FIG. 3 and the specifications shown in Table 3.
(Wet brake performance)
Each test tire is assembled on a standard rim, the internal pressure is adjusted to the vehicle specified pressure, and then mounted on the vehicle. After running on a stagnant road surface with an average water depth of 2 mm at a speed of 80 km / h, braking is applied suddenly. The distance was measured. The results are shown as an index with the performance of the inventive tire 3-1 as 100. In addition, it shows that it is excellent in performance, so that a numerical value (deceleration index | exponent) is large.

  From Table 3, the invention example tire having the rubber sheet 7 and the loss tangent of the rubber sheet 7, the base rubber layer 6B, and the cap rubber layer 6C satisfies the relationship of rubber sheet <base rubber layer <cap rubber layer It can be seen that 3-1 maintains a low rolling resistance and is excellent in wet brake performance.

2 carcass 3a inclined belt layer 3b inclined belt layer 4a circumferential belt layer 4b circumferential belt layer 6 tread 6C cap rubber layer 6B base rubber layer 7 rubber sheet 8 cushion rubber 9 circumferential groove 10 side rubber

Claims (3)

A tread in which a carcass extending in a toroid shape between a pair of bead cores is used as a skeleton, and a belt composed of a plurality of belt layers and a plurality of circumferential grooves extending along the tire equatorial plane are formed on the outer side in the radial direction of the carcass. In pneumatic tires,
The tread consists of at least one tread rubber layer,
Among the end portions of the plurality of belt layers, a rubber sheet is disposed between the belt and the tread rubber layer so as to cover an end portion located on the outermost side in the tire width direction,
Loss tangent of the rubber sheet at 60 ° C. is rather low than the loss tangent of the tread rubber layer,
The tire width direction inner side edge part of the rubber sheet is 10 mm or more outside in the tire width direction outside the tire width direction outer side edge part of the outermost circumferential groove in the tire width direction among the plurality of circumferential grooves,
A pneumatic sheet characterized in that an outer end portion in the tire width direction of the rubber sheet is 10 mm or more and 20 mm or less in an outer portion in the tire width direction from an end portion of the plurality of belt layers located on the outermost side in the tire width direction. tire.   The carcass is folded from the carcass main body portion extending in a toroidal shape between the pair of bead cores, from the inner side to the outer side in the tire width direction around the bead core, and extends between the belt and the carcass main body portion. The pneumatic tire according to claim 1, further comprising a carcass folded portion. The tread is composed of a base rubber layer and a cap rubber layer radially outside the base rubber layer,
The loss tangent tan δg of the rubber sheet at 60 ° C., the loss tangent tan δb of the base rubber layer, and the loss tangent tan δc of the cap rubber layer are:
tan δg <tan δb <tan δc
The pneumatic tire according to claim 1 or 2, characterized by satisfying the relationship.

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