JP5568952B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire. More specifically, the present invention relates to a pneumatic radial tire that reduces rolling resistance without impairing riding comfort and durability in a tire obtained by dividing a carcass layer in a central region of a tread portion. Regarding tires.

  In order to improve the weight reduction and riding comfort of a pneumatic tire, the carcass layer forming the tire skeleton has been divided in the central region of the tread portion and left and right separated (for example, Patent Document 1). reference). However, in this type of tire, because the side rigidity of the tire is insufficient, it becomes difficult to ensure good steering stability and durability, and at the same time, with the increase in the tire outer diameter in the tread central region, There is a problem that the contact length of the tread surface increases and rolling resistance deteriorates.

  As countermeasures, in order to improve rolling resistance and achieve both ride comfort and handling stability, the tire shape during inflation filled with air pressure is changed to the cavity shape in the vulcanization mold. There is a proposal that is specified by the relationship (see Patent Document 2). However, in this proposal, although the improvement effect of steering stability is recognized to some extent, the improvement effect of rolling resistance is limited, and further improvement has been demanded.

JP 2007-283962 A JP 2001-187512 A

  An object of the present invention is to provide a pneumatic radial tire in which rolling resistance is reduced without impairing riding comfort and durability in a tire in which a carcass layer is divided in a central region of a tread portion. .

In the pneumatic radial tire of the present invention that achieves the above object, at least one carcass layer made of a reinforcing cord oriented in the tire radial direction is mounted between a pair of left and right bead portions, and the outer periphery of the carcass layer in the tread portion. In a pneumatic radial tire in which at least two belt layers whose cord directions are crossed between the layers are arranged on the side and the carcass layer is divided in a central region of the tread portion to form a divided portion, the belt layer is An organic fiber cord that is made of a steel cord and is spirally wound at an angle of 0 to 5 ° with respect to the tire circumferential direction in a central region corresponding to at least a split portion of the carcass layer on the outer peripheral side of the belt layer A belt cover layer made of, and the outer peripheral length of the tread portion along the tire equatorial plane at the time of non-inflation of the vulcanized tire CN, when the outer peripheral length of the tread portion at a position corresponding to 70% of the tire contact width with respect to the tire equatorial plane is defined as DSN, the relationship between DCN and DSN is DCN ≦ DSN, and inflation DCI and DSI when the outer peripheral length of the tread portion along the tire equatorial plane at the time is DCI and the outer peripheral length of the tread portion at a position corresponding to 70% of the tire ground contact width around the tire equatorial plane is DSI. The relationship is that DCI> DSI.

Furthermore, in the structure mentioned above, it is preferable to comprise as described in (1)-(4) below.
(1) The belt cover layer covers the entire outer peripheral side of the belt layer, or the central region and both ends.
(2) The organic fiber cord constituting the belt cover layer is composed of at least one selected from nylon fiber, polyester fiber, rayon fiber, and vinylon fiber.
(3) The dividing width A at the dividing portion of the carcass layer is set to 10 to 95% of the belt maximum width BW of the belt layer.
(4) The belt cover represented by the product of the residual tension S of the organic fiber cords constituting the belt cover layer in the vulcanized tire and the number E of driven organic fiber cords per 1 cm width of the belt cover layer. The belt tightening index S × E of the layer is set to 150 to 300 at least at a position corresponding to the divided portion of the carcass layer.

According to the present invention, in the tire in which the carcass layer is divided in the central region of the tread portion, the tire extends substantially in the tire circumferential direction in the central region corresponding to at least the split portion of the carcass layer on the outer peripheral side of the belt layer made of steel cord. A belt cover layer made of an organic fiber cord is disposed, and both the outer peripheral length of the tread portion along the tire equatorial plane (hereinafter referred to as the center outer peripheral length) and 70% of the tire ground contact width centered on the tire equatorial plane. The relationship between the outer circumference of the tread at the shoulder position (hereinafter referred to as the shoulder outer circumference) is “center outer circumference ≦ shoulder outer circumference” when not inflated, and “center outer circumference> shoulder outer circumference when inflated. The tension of the belt cover layer in the tire after inflation is increased. While ensuring good riding comfort by dividing the carcass layer in the center area of the head part, durability is ensured by the tagging effect of the belt cover layer, and at the same time, the contact length of the tread surface is increased by increasing the tension of the belt cover layer. It can be optimized to reduce rolling resistance.

It is sectional drawing which shows an example of the pneumatic radial tire by embodiment of this invention. It is explanatory drawing in the case of measuring the outer periphery length of the tread part in the position in which the groove | channel was formed. It is explanatory drawing which shows arrangement | positioning of the reinforcement layer in the pneumatic radial tire by other embodiment of this invention. It is explanatory drawing equivalent to FIG. 3 which shows arrangement | positioning of the reinforcement layer in the pneumatic radial tire by further another embodiment of this invention.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing an example of a pneumatic radial tire according to an embodiment of the present invention. In FIG. 1, a pneumatic radial tire 1 is mounted with at least one carcass layer 3 (one layer in the figure) made of a reinforcing cord oriented in the tire radial direction between a pair of left and right bead portions 2, 2, In the tread portion 4, at least two belt layers 5 and 6 (two layers in the figure) whose cord directions cross each other are disposed on the outer peripheral side of the carcass layer 3, and the carcass layer 3 is disposed in the central region of the tread portion 4. Dividing part Q is formed by dividing.

In the pneumatic radial tire 1 of the present invention, the belt layers 5 and 6 are made of steel cords, and the tire circumference is at least in the central region corresponding to the dividing portion Q of the carcass layer 3 on the outer peripheral side of the belt layers 5 and 6. A tread along the tire equatorial plane CL when the vulcanized tire is not inflated by arranging a belt cover layer 7 made of an organic fiber cord spirally wound at an angle of 0 to 5 ° with respect to the direction When the outer peripheral length of the tread portion 4 at the positions P and P corresponding to 70% of the tire ground contact width TW with respect to the tire equatorial plane CL is defined as DCN as the outer peripheral length of the portion 4, the relationship between DCN and DSN is DCN ≦ DSN, preferably DCN <DSN, and the outer peripheral length of the tread portion 4 along the tire equatorial plane CL during inflation is DCI, while the tire equatorial plane CL is Tire position P corresponding to 70% of the ground contact width TW, when the DSI the outer peripheral length of the tread portion 4 in the P, the relationship between the DCI and the DSI is set to be DCI> DSI as.

  As described above, the pneumatic radial tire 1 according to the present invention has an outer peripheral length of the tread portion 4 (hereinafter referred to as a center outer peripheral length) along the tire equatorial plane CL and 70% of the tire ground contact width TW around the tire equatorial plane CL. The relationship between the size of the outer circumference of the tread portion 4 at the positions P and P (hereinafter referred to as the shoulder outer circumference length) is reversed between non-inflation and inflation, and the tread portion is non-inflation. The surface of 4 is formed in a flat or concave shape, and the surface of the tread portion 4 is formed in a convex shape as the air pressure is filled.

  As a result, the tension of the belt cover layer 7 in the tire after inflation is increased. Therefore, the belt cover layer 7 has a tagging portion while ensuring good riding comfort by dividing the carcass layer 3 in the central region of the tread portion 4. The durability can be ensured by the effect, and at the same time, the contact length of the tread surface can be optimized by increasing the tension of the belt cover layer 7 to reduce the rolling resistance.

  The above-described outer perimeter of the tread portion 4 is a value obtained when the tire is mounted on an applicable rim (standard rim) and is not filled with air pressure when not inflated in accordance with the tire measurement method stipulated by the JATMA standard. Is applied, the tire is mounted on the applied rim (standard rim) at the time of inflation, filled with the highest air pressure (air pressure corresponding to the maximum load capacity) and left at room temperature (15 to 30 ° C.) for 24 hours, The value when adjusted to the original air pressure and measured again is applied. However, in the case of passenger car tires, this filling air pressure is set to 180 kPa in accordance with the above-mentioned standard.

  In the present invention, when grooves are formed on the surface of the tread portion 4 at the positions P and P corresponding to 70% of the tire contact width TW on the tire equatorial plane CL, as shown in FIG. The outer peripheral length on the virtual extension line R which connects the surfaces 4a and 4a of the tread portion 4 straddling is applied.

  Note that the tire ground contact width TW described above refers to a tire that is filled with air pressure corresponding to the maximum load capacity specified by JATMA and placed vertically on a flat plate, and a load corresponding to 80% of the maximum load capacity is applied. This is the maximum linear distance in the tire axial direction on the ground contact surface formed on the flat plate.

  In the present invention, the type of the organic fiber cord constituting the belt cover layer 7 is not particularly limited, but the heat-shrinkable organic fiber such as nylon fiber cord, polyester fiber cord, rayon fiber cord, vinylon fiber cord, etc. A code is preferably used. Thereby, the tagging effect of the belt layers 5 and 6 in the tire after vulcanization is enhanced, and in the tire after inflation in combination with the relationship between the size of the center outer circumference length and the shoulder outer circumference length before and after the inflation described above. The tension of the belt cover layer 7 is increased, and accordingly, the contact length of the tread surface is optimized and the rolling resistance can be surely reduced.

  In the present invention, the dividing width A at the dividing portion Q of the carcass layer 3 described above may be set to 10 to 95%, preferably 45 to 85% of the belt maximum width BW of the belt layers 5 and 6. Thereby, rolling resistance can be reliably reduced, maintaining favorable riding comfort and durability. Here, if the dividing width A is less than 10% of the belt maximum width BW, the relationship between the center outer circumference length and the shoulder outer circumference length before and after inflation cannot be maintained, and the effect of reducing rolling resistance cannot be obtained. If it exceeds%, the durability will be reduced.

  In the present invention, more preferably, the product of the residual tension S of the organic fiber cords constituting the belt cover layer 7 in the vulcanized tire and the number E of driven organic fiber cords per 1 cm width of the belt cover layer 7 is represented by The belt tightening index S × E is adjusted to be 150 to 300, preferably 180 to 250, at least at a position corresponding to the divided portion Q of the carcass layer 3. Thereby, since the tension of the belt cover layer 7 in the tire after inflation is reliably increased, the contact length of the tread surface can be optimized by increasing the tension of the belt cover layer 7 to reliably reduce the rolling resistance. it can.

  Here, when the belt tightening index S × E is less than 150, the tension of the belt cover layer 7 in the tire after inflation is insufficient, so that it is difficult to obtain an effect of reducing rolling resistance due to an increase in the contact length of the tread surface. When the tightening index S × E exceeds 300, the tension of the belt cover layer 7 increases excessively, the variation in the contact length of the tread surface increases, and uneven wear tends to occur, and at the same time, the rolling resistance is reduced. It becomes difficult to obtain.

  The above-described residual tension S means the length La of the organic fiber cord in the vulcanized tire, and the cord is taken from the tire and then pulled with a load of 1/20 g per 1d of the displayed fineness of the cord. The tension (N) when the tension (N) corresponding to the difference (La-Lb) from the measured length Lb is collated with the tension-strain curve obtained in accordance with JIS L1017.

  Specifically, a part of the tread rubber of the tire after vulcanization is removed to expose the cover cord constituting the belt cover layer, and a predetermined length La (for example, 500 mm) along the exposed cover cord. ), And then measuring the length when the cover cord is cut from the tire and then pulled with a predetermined load corresponding to the displayed fineness of the cord, and the length Lb at that time is measured. The tension (N) corresponding to the difference (La−Lb) is obtained by collating with a tension-strain curve obtained in accordance with JIS L1017.

  In the embodiment shown in FIG. 1, the belt cover layer 7 is disposed so as to cover the entire area and both ends of the belt layers 5 and 6. However, in the pneumatic radial tire 1 of the present invention, the belt The cover layer 7 may be disposed so as to cover only the entire width of the belt layers 5 and 6 as shown in FIG. Furthermore, the belt cover layer 7 may be divided into a central area on the outer peripheral side of the belt layers 5 and 6 and both ends.

  FIG. 4 is an explanatory view showing the arrangement of the carcass layer 3 and the belt cover layer 7 in a pneumatic radial tire according to another embodiment of the present invention. In this embodiment, the carcass layer 3 is divided into an inner carcass layer 3a and an outer carcass layer. 3b and the carcass layers 3a and 3b have different dividing widths. In the present embodiment, the case where the dividing width of the inner carcass layer 3a is formed narrower than the dividing width of the outer carcass layer 3b is shown, but the relationship between the sizes of these dividing widths is not limited to this. Absent.

  In the present embodiment, three belt cover layers 7 are provided on the outer peripheral side of the belt layers 5 and 6 and the outer peripheral sides of both ends of the belt layers 5 and 6 corresponding to the divided portions of the carcass layers 3a and 3b. The parts 7a, 7b and 7b are divided and arranged. Here, both ends of the belt cover layer 7a arranged in the central region of the belt layers 5 and 6 can be extended to the inside of the belt cover layers 7b and 7b as in the embodiment of FIG.

  In the embodiment of FIG. 4, from the viewpoint of ensuring durability, the dividing width between the inner carcass layer 3a and the outer carcass layers 3b and 3b is set to be 10 to 95% of the maximum belt width BW, respectively. doing.

  As described above, in the pneumatic radial tire of the present invention, the belt cover layer is disposed in the central region corresponding to at least the split portion of the carcass layer on the outer peripheral side of the belt layer, and before and after inflation of the tire after vulcanization. By maintaining a predetermined relationship between the center outer circumference length and the shoulder outer circumference length, while maintaining good riding comfort, it ensures durability and at the same time reduces rolling resistance. It can be preferably applied to high-performance vehicles that place importance on rolling resistance.

  Conventional tires (conventional examples), tires of the present invention (Examples 1 to 5) having a tire size of 235 / 40R18, a tire structure as shown in FIG. ) And comparative tires (Comparative Examples 1 to 4). In each tire, a nylon fiber cord was used for the belt cover layer, a polyester fiber cord for the carcass layer, and a steel cord for the belt layer.

  About these 10 types of tires, rolling resistance, riding comfort and durability were evaluated by the test methods described below, and the results are also shown in Table 1 using an index with the conventional example being 100. It shows that it is excellent, so that this figure is large.

[Rolling resistance]
Each tire is incorporated into a rim (size: 8.5J), filled with an internal pressure of 230 kPa, and loaded with a load of 4.5 kN with an indoor drum tester (drum diameter: 1707 mm), with a speed of 80 km / h. The rolling resistance value when running was measured, and the rolling resistance value was evaluated by the inverse value.

[Ride comfort]
Each tire is assembled in a rim (size: 8.5J), filled with an internal pressure of 230 kPa, mounted on the front and rear wheels of a passenger car with a displacement of 3000L, and then a straight test course with irregularities is run at a speed of 50km / h. Then, sensory evaluation was performed by three skilled panelists, and the evaluation points were averaged to evaluate riding comfort.

〔durability〕
Each tire was incorporated into a rim (size: 8.5 J), and water pressure was applied until the tire broke, and the durability was evaluated using the water pressure when the tire broke.

  From Table 1, it can be seen that the rolling resistance of the tire of the present invention is reduced while maintaining riding comfort and durability as compared with the conventional tire.

DESCRIPTION OF SYMBOLS 1 Pneumatic radial tire 2 Bead part 3, 3a, 3b Carcass layer 4 Tread part 5, 6 Belt layer 7, 7a, 7b Belt cover layer CL Tire equatorial plane Q Carcass layer part A Carcass layer part width BW Belt maximum Large TW tire contact width

Claims (6)

At least one carcass layer made of reinforcing cords oriented in the tire radial direction is mounted between a pair of left and right bead portions, and at least two layers in which the cord directions cross each other on the outer peripheral side of the carcass layer in the tread portion. In a pneumatic radial tire in which a belt layer is disposed and the carcass layer is divided in a central region of the tread portion to form a split portion.
The belt layer is formed of a steel cord and is spirally wound at an angle of 0 to 5 ° with respect to the tire circumferential direction at a position corresponding to at least a split portion of the carcass layer on the outer peripheral side of the belt layer. A belt cover layer made of an organic fiber cord is arranged, and the outer peripheral length of the tread portion along the tire equatorial plane when the vulcanized tire is not inflated is DCN, and the tire ground contact width is 70 around the tire equatorial plane. %, The relationship between DCN and DSN is DCN ≦ DSN, and the outer circumference of the tread portion along the tire equator line at the time of inflation When DCI is the length and DSI is the outer peripheral length of the tread portion at a position corresponding to 70% of the tire ground contact width centered on the tire equator line, A pneumatic radial tire the relationship between SI was set to be the DCI> DSI.   The pneumatic radial tire according to claim 1, wherein the belt cover layer is disposed so as to cover the entire outer peripheral side of the belt layer.   2. The pneumatic radial tire according to claim 1, wherein the belt cover layer is disposed so as to cover a central area and both ends of the outer peripheral side of the belt layer.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the organic fiber cord constituting the belt cover layer is at least one selected from nylon fiber, polyester fiber, rayon fiber, and vinylon fiber.   The pneumatic radial tire according to any one of claims 1 to 4, wherein a dividing width A at a dividing portion of the carcass layer is 10 to 95% of a belt maximum width BW of the belt layer.   The belt cover layer represented by the product of the residual tension S of the organic fiber cords constituting the belt cover layer in the non-inflated tire and the number E of driven organic fiber cords per 1 cm width of the belt cover layer. The pneumatic radial tire according to any one of claims 1 to 4, wherein a belt tightening index SxE is set to 150 to 300 at least at a position corresponding to a divided portion of the carcass layer.

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