tire

Abstract

To provide a tire capable of improving steering stability performance while maintaining excellent abrasion resistance performance.SOLUTION: There is provided a tire 1 in which a plurality of grooves 3 are formed in a tread part 2. in the tread part 2, in a normal state, a contact surface 2a when a normal load is applied thereto at a camber angle of 0° has a contact length L that is a length in the tire circumferential direction related to each position in a tire axial direction, and a contact semi-width Tw that is a distance between a tire equator C and a contact end Te that is an outer end in the tire axial direction of the contact surface 2a. The contact length L includes a crown contact length LC at the tire equator C, and a shoulder contact length LS at a position separated from the tire equator C by 80% of the contact semi-width Tw. The crown contact length LC is 0.95 to 1.05 times of the shoulder contact length LS. When a reference virtual groove G0 set at a groove depth d0 predetermined at the tire equator C is defined, each groove depth d of the plurality of grooves 3 satisfies a predetermined expression.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire having a tread portion. [Background technology]

[0002] Conventionally, tires having a tread portion in which a plurality of circumferential grooves extending in the tire circumferential direction are formed have been known. For example, Patent Document 1 listed below proposes a tire in which wear resistance is improved by specifying the profile of a tread portion in which a plurality of circumferential main grooves are formed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-182339 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the tire of Patent Document 1, the groove depth of the main grooves is the same, and the rigidity of the tread portion is reduced by the main grooves with a larger groove depth, so further improvement in steering stability performance has been desired.

[0005] The present invention has been devised in view of the above circumstances, and has as its main object to provide a tire that can improve steering stability while maintaining excellent wear resistance. [Means for solving the problem]

[0006] The present invention provides a tire having a tread portion, the tread portion having a plurality of grooves formed therein, wherein the tread portion, when mounted on a regular rim and adjusted to a regular internal pressure, has a contact patch when a regular load is applied with a camber angle of 0° and has a contact length which is a circumferential length of the tire associated with each position in the tire axial direction, and a contact half width which is the distance from the tire equator to the contact edge which is the outermost end of the contact patch in the tire axial direction, the contact length including a crown contact length at the tire equator and a shoulder contact length at a position away from the tire equator by 80% of the contact half width, the crown contact length being 0.95 to 1.05 times the shoulder contact length, and wherein when a reference virtual groove set to a predetermined groove depth is defined at the tire equator, a groove depth d of each of the plurality of grooves satisfies the following formula (1):

number

[0007] In the tire of the present invention, the grooves include a plurality of circumferential grooves extending in the tire circumferential direction, and when the reference imaginary groove, a first imaginary groove set at a first position axially separated from the tire equator, a second imaginary groove set at a second position axially outward from the first position, a third imaginary groove set at a third position axially outward from the second position, and an imaginary line tangent to the groove bottoms of the reference imaginary groove, the groove bottoms of the first imaginary groove, the groove bottoms of the second imaginary groove, and the groove bottoms of the third imaginary groove are defined in a tire meridian cross section in the normal state without load, the groove depth of the circumferential groove is within ±10% of the distance from the outer surface of the tread portion to the imaginary line at the axial position where the circumferential groove is formed, and the groove depth d1 of the first imaginary groove, the groove depth d2 of the second imaginary groove, and the groove depth d3 of the third imaginary groove are desirably determined based on the following formulas (2) to (4).

number

number

number

[0008] In the tire of the present invention, it is desirable that the first position is a position that is 40% to 55% of the half contact width from the tire equator, the second position is a position that is 75% to 80% of the half contact width from the tire equator, and the third position is a position that is 90% to 85% of the half contact width from the tire equator.

[0009] In the tire of the present invention, the correction coefficient is preferably a positive number of 2.0 or less.

[0010] In the tire of the present invention, the correction coefficient is preferably 0.8 to 1.2.

[0011] In the tire of the present invention, it is desirable that the circumferential grooves include a first circumferential groove on the axially inner side of the tire and a second circumferential groove on the axially outer side of the tire, and that the groove depth of the second circumferential groove is greater than the groove depth of the first circumferential groove.

[0012] In the tire of the present invention, it is preferable that the grooves include a plurality of lateral grooves extending in the tire axial direction. [Effects of the Invention]

[0013] In the tire of the present invention, the contact length includes a crown contact length at the tire equator and a shoulder contact length at a position 80% of the contact half width from the tire equator, and the crown contact length is 0.95 to 1.05 times the shoulder contact length. Such a tire has a large contact area and can improve cornering power, thereby improving steering stability.

[0014] In the tire of the present invention, when a reference virtual groove is defined as a predetermined groove depth centered on the tire equator, the groove depth d of each of the plurality of grooves satisfies the above formula (1). Such grooves can prevent the groove depth from becoming excessively large in response to wear amounts that vary depending on the axial position of the tire, and improve the rigidity of the tread portion, thereby improving cornering power. Therefore, the tire of the present invention can improve steering stability while maintaining excellent wear resistance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a schematic diagram of a tread portion of a tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the contact surface of the tread portion. [Figure 3] FIG. 4 is a cross-sectional view showing a tread portion of another embodiment. [Figure 4] 3 is a flowchart illustrating an embodiment of a groove depth setting method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 1 is a schematic cross-sectional view of a tire meridian showing a tread portion 2 of a tire 1 in a normal state according to this embodiment. The tire 1 according to this embodiment is suitably used as a pneumatic tire for passenger cars. The tire 1 is not limited to pneumatic tires for passenger cars, and can be used for various tires such as pneumatic tires for heavy loads, pneumatic tires for motorcycles, and non-pneumatic tires that do not have pressurized air filled inside the tire.

[0017] Here, "normal state" means, in the case where the tire 1 is a pneumatic tire, a state in which the tire 1 is mounted on a normal rim, adjusted to a normal internal pressure, and no load is applied. Unless otherwise specified in this specification, the dimensions of each part of the tire 1 are values measured in the normal state.

[0018] "Genuine rim" is a rim that is determined for each tire by a standard system that includes the standard on which tire 1 is based, for example, "standard rim" for JATMA, "Design Rim" for TRA, and "Measuring Rim" for ETRTO. "Genuine rim" is a rim that is determined for each tire by the manufacturer, etc., if there is no standard system that includes the standard on which tire 1 is based.

[0019] "Normal internal pressure" is the air pressure set for each tire by a standard set by each standard, if there is one that includes the standard on which tire 1 is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE." If there is no standard set that includes the standard on which tire 1 is based, "normal internal pressure" is the air pressure set for each tire by the manufacturer, etc.

[0020] As shown in Fig. 1, a tire 1 of this embodiment has a tread portion 2 that comes into contact with the road surface during running. The tread portion 2 of this embodiment has a plurality of grooves 3 formed therein. The grooves 3 include a plurality of circumferential grooves 4 (four in this embodiment) extending in the circumferential direction of the tire, and a plurality of lateral grooves 5 extending in the axial direction of the tire.

[0021] The circumferential grooves 4 include, for example, a crown circumferential groove 4A arranged on the tire equator C side and a shoulder circumferential groove 4B arranged axially outward of the crown circumferential groove 4A. Such a tire 1 has good drainage performance when traveling on wet roads due to the plurality of grooves 3.

[0022] Fig. 2 is a schematic diagram showing a contact patch 2a of the tread portion 2. As shown in Fig. 2, in the tread portion 2 of this embodiment, in a normal state, when a normal load is applied with a camber angle of 0°, the contact patch 2a has a contact length L, which is the length in the tire circumferential direction associated with each position P in the tire axial direction. The contact patch 2a of this embodiment has a contact half width Tw, which is the distance from the tire equator C to the contact edge Te, which is the outer end of the contact patch 2a in the tire axial direction. The tire equator C is the center position between the contact edges Te on both sides in the tire axial direction.

[0023] Here, "normal load" refers to the load determined for each tire by a standard system that includes the standard on which tire 1 is based, if such a system exists; for example, it is "maximum load capacity" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO. If there is no standard system that includes the standard on which tire 1 is based, "normal load" refers to the load determined for each tire by the manufacturer, etc.

[0024] The contact length L includes, for example, a crown contact length LC at the tire equator C and a shoulder contact length LS at a position P1 that is a distance W1 that is 80% of the half contact width Tw from the tire equator C. In this embodiment, the crown contact length LC is 0.95 to 1.05 times the shoulder contact length LS. Such a tire 1 has a large contact area and can improve cornering power, thereby improving steering stability.

[0025] As shown in Figures 1 and 2, when a reference virtual groove G0 is defined at the tire equator C with a predetermined groove depth d0, the groove depth d of each of the multiple grooves 3 in this embodiment satisfies the following formula (1).

number

[0026] Such grooves 3 can prevent the groove depth d from becoming excessively large in response to the amount of wear that varies depending on the axial position of the tire, and can improve cornering power because of the improved rigidity of the tread portion 2. Therefore, the tire 1 of this embodiment can improve steering stability while maintaining excellent wear resistance.

[0027] In a more preferred embodiment, the groove depth d0 of the reference imaginary groove G0 is defined based on the groove depth d of the circumferential groove 4 arranged adjacent to the tire equator C. That is, the groove depth d0 of the reference imaginary groove G0 is defined as the distance between the tire equator C and a curve connecting the groove bottoms of the crown circumferential grooves 4A arranged adjacent to the tire equator C with the same curvature radius R as the outer surface 2b.

[0028] Fig. 3 is a schematic cross-sectional view of a tire meridian showing a tread portion 2 of a tire 1 in a normal state according to another embodiment. As shown in Fig. 3, three circumferential grooves 4 are formed in the tread portion 2 of the tire 1 of this embodiment. One of the circumferential grooves 4 of this embodiment is formed on the tire equator C.

[0029] The groove depth d0 of the reference imaginary groove G0 in this embodiment is defined as the groove depth d of the circumferential groove 4 arranged on the tire equator C. The groove depth d0 of such a reference imaginary groove G0 is clearly defined. Note that the number of circumferential grooves 4 is not limited to this and may be, for example, two or five or more.

[0030] 1 and 2, the groove depth d of the circumferential groove 4 is preferably determined based on a virtual line VL defined on a meridian cross section of the tire in a normal, no-load state. The virtual line VL in this embodiment is defined on the meridian cross section of the tire in a normal, no-load state based on a reference virtual groove G0, a first virtual groove G1, a second virtual groove G2, and a third virtual groove G3 set in the tread portion 2.

[0031] Here, the reference imaginary groove G0 is a virtual circumferential groove set at the tire equator C. The first imaginary groove G1 is a virtual circumferential groove set at a first position P1 axially separated from the tire equator C. The second imaginary groove G2 is a virtual circumferential groove set at a second position P2 axially outward of the first position P1. The third imaginary groove G3 is a virtual circumferential groove set at a third position P3 axially outward of the second position P2.

[0032] Such imaginary line VL can optimize the groove depth d of the circumferential groove 4 with respect to the amount of wear and can improve the rigidity of the tread portion 2, thereby improving the steering stability of the tire 1. In addition, the imaginary line VL is useful for reducing the thickness t of the tread rubber 2g of the tread portion 2 and can reduce the weight of the tire 1, thereby improving the fuel efficiency of the tire 1. The thickness t of the tread rubber 2g is defined as the distance between the outer surface 2b of the tread portion 2 and the belt layer B arranged in the tread portion 2.

[0033] The contact length L includes, for example, a first contact length L1 at the first position P1, a second contact length L2 at the second position P2, and a third contact length L3 at the third position P3. The first contact length L1, the second contact length L2, and the third contact length L3 are useful for accurately defining the virtual line VL.

[0034] The groove depth d1 of the first imaginary groove G1 is preferably determined based on the following formula (2).

number

[0035] The groove depth d2 of the second imaginary groove G2 is preferably determined based on the following formula (3).

number

[0036] The groove depth d3 of the third imaginary groove G3 is preferably determined based on the following formula (3).

number

[0037] The correction coefficient α is preferably a positive number equal to or less than 2.0. When the correction coefficient α is equal to or less than 2.0, excessive correction based on the differences between the crown contact length LC and the first contact length L1, second contact length L2, and third contact length L3 can be prevented. When the correction coefficient α is a positive number, correction based on the differences between the crown contact length LC and the first contact length L1, second contact length L2, and third contact length L3 can be reliably made. From this perspective, the correction coefficient α is more preferably 0.8 to 1.2.

[0038] The imaginary line VL in this embodiment is defined so as to be tangent to the groove bottom of the reference imaginary groove G0, the groove bottom of the first imaginary groove G1, the groove bottom of the second imaginary groove G2, and the groove bottom of the third imaginary groove G3. The groove depth d of the circumferential groove 4 in this embodiment is within ±10% of the distance Ld from the outer surface 2b of the tread portion 2 to the imaginary line VL at the position P in the tire axial direction where the circumferential groove 4 is formed.

[0039] Such circumferential grooves 4 can prevent the groove depth d from becoming excessively large relative to the amount of wear that varies depending on the axial position P of the tire, thereby improving the rigidity of the tread portion 2. Therefore, the tire 1 of this embodiment can improve steering stability while maintaining excellent wear resistance.

[0040] The first position P1 is preferably a position separated by a distance W1 of 40% to 55% of the half contact width Tw from the tire equator C. The first position P1 is located, for example, in the middle land portion 6 between the crown circumferential groove 4A and the shoulder circumferential groove 4B.

[0041] The second position P2 is preferably located a distance W2 that is 75% to 80% of the half contact width Tw from the tire equator C. The second position P2 is located, for example, in the shoulder land portion 7 that is axially outward of the shoulder circumferential groove 4B. The second contact length L2 is equal to the shoulder contact length LS, for example, when the distance W2 is 80% of the half contact width Tw.

[0042] The third position P3 is preferably a position separated by a distance W3 of 90% to 85% of the half contact width Tw from the tire equator C. The third position P3 is located, for example, in the shoulder land portion 7 axially outward of the shoulder circumferential groove 4B.

[0043] Such a virtual line VL can be precisely defined over the entire range from the tire equator C to the ground contact edge Te by the reference virtual groove G0, the first virtual groove G1, the second virtual groove G2, and the third virtual groove G3.

[0044] The circumferential grooves 4 of this embodiment include a first circumferential groove on the axially inner side of the tire and a second circumferential groove on the axially outer side of the tire. The first circumferential groove is, for example, a crown circumferential groove 4A. The second circumferential groove is, for example, a shoulder circumferential groove 4B. The groove depth of the second circumferential groove of this embodiment is greater than the groove depth of the first circumferential groove. With such circumferential grooves 4, the remaining groove depth becomes equal when the tread portion 2 wears, and it is possible to achieve both durability and fuel efficiency due to weight reduction.

[0045] The groove depth d of the lateral grooves 5 in this embodiment is equal to or less than the distance Ld from the outer surface 2b to the imaginary line VL at the axial position P where the lateral grooves 5 are formed. The groove bottom of the lateral grooves 5 may extend along the imaginary line VL, for example. Such an imaginary line VL can optimize the maximum value of the groove depth d of the lateral grooves 5.

[0046] Next, with reference to Figures 1 to 3, a method for setting the groove depth d of the circumferential grooves 4 in a tire 1 having a tread portion 2 in which a plurality of circumferential grooves 4 extending in the tire circumferential direction are formed will be described.

[0047] Fig. 4 is a flowchart showing the groove depth setting method of this embodiment. As shown in Fig. 4, the groove depth setting method of this embodiment first performs a first step S1 of identifying the contact patch 2a of the tread portion 2 when a normal load is applied in a normal state with a camber angle of 0°. In the first step S1, the contact patch 2a may be identified, for example, by a computer simulation or experimentally. This first step S1 can accurately identify the shape of the contact patch 2a.

[0048] In the groove depth setting method of this embodiment, after the first step S1, a second step S2 is performed to determine the contact length L, which is the circumferential length of the tire associated with each axial position P of the contact patch 2a. In this embodiment, the second step S2 determines at least the crown contact length LC and the shoulder contact length LS. Preferably, the second step S2 further determines the first contact length L1, the second contact length L2, and the third contact length L3. This second step S2 does not require determining the contact lengths L associated with all axial positions P, thereby reducing calculation time.

[0049] In the groove depth setting method of this embodiment, after the second step S2, a third step S3 is performed in which a reference imaginary groove G0, a first imaginary groove G1, a second imaginary groove G2, and a third imaginary groove G3 are set. In the third step S3, for example, a groove depth d0 of the reference imaginary groove G0, a groove depth d1 of the first imaginary groove G1, a groove depth d2 of the second imaginary groove G2, and a groove depth d3 of the third imaginary groove G3 are obtained.

[0050] In the groove depth setting method of this embodiment, after the third step S3, a fourth step S4 is performed to define a virtual line VL that is tangent to the groove bottom of the reference virtual groove G0, the groove bottom of the first virtual groove G1, the groove bottom of the second virtual groove G2, and the groove bottom of the third virtual groove G3.

[0051] In the groove depth setting method of this embodiment, after the fourth step S4, a fifth step S5 is performed in which the groove depth d of the circumferential grooves 4 is set so that the groove bottom is located on the imaginary line VL. This groove depth setting method can optimize the groove depth d of the circumferential grooves 4 to accommodate the amount of wear that varies depending on the position in the tire axial direction, thereby improving the rigidity of the tread portion 2. Therefore, the groove depth setting method of this embodiment can improve the steering stability of the tire 1 while maintaining excellent wear resistance.

[0052] In addition, the groove depth may be set, for example, by defining a virtual circle having a center on the outer surface 2b of the tread portion 2, instead of the virtual groove, to define the virtual line VL.

[0053] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment and can be modified and practiced in various ways. [Example]

[0054] Example tires having the basic structure shown in Figure 1 and circumferential groove depths based on formulas (2) to (4) were prototyped based on the specifications in Table 1. As a comparative example, a tire with the same circumferential groove depth was prototyped. These prototype tires were tested for wear resistance, steering stability, noise performance, and fuel economy. The common specifications and test methods for each prototype tire are as follows:

[0055] <Common specifications> Tire size: 255 / 65R18 Rim size: 18 x 7.5J

[0056] <Wear resistance> Each prototype tire was fitted to all wheels of a vehicle, and the vehicle was driven 20,000 km on a dry paved road. The amount of wear was measured at multiple different positions in the tire axial direction, and the amount of wear at the position with the most advanced wear was evaluated. The results were expressed as an index, with Comparative Example 1 being set at 100, and the higher the index, the less advanced the wear and the better the wear resistance.

[0057] <Handling stability> Each prototype tire in its normal state was mounted on a flat belt testing machine, and cornering power was measured when the tire was run at 30 km / h with a normal load and a slip angle of 1°. The results were expressed as an index with Comparative Example 1 being set at 100, with a higher index indicating greater cornering power and better handling stability.

[0058] <Noise performance> Each prototype tire was mounted on all wheels of a running vehicle, and the vehicle's external noise was measured when the vehicle was driven on a road noise measurement surface. The results were expressed as an index, with Comparative Example 1 being set at 100, and the higher the index, the lower the external noise and the better the noise performance.

[0059] <Low fuel consumption performance> The weight of each prototype tire was measured. The results were expressed as an index with Comparative Example 1 being 100, with a larger index indicating a lighter weight and better fuel economy.

[0060] The test results are shown in Table 1. [Table 1]

[0061] As a result of the test, it was confirmed that the tires of the examples had improved steering stability while maintaining the same wear resistance as the comparative example, and were also superior in noise performance and fuel economy. [Explanation of symbols]

[0062] 1 tire 2 Tread section 2a Ground plane 3 grooves

Claims

1. A tire having a tread portion, A plurality of grooves are formed in the tread portion, The tread portion has a contact patch that has a contact length, which is a length in the tire circumferential direction associated with each position in the tire axial direction, and a contact edge, which is the outermost end in the tire axial direction, when the tread portion is mounted on a normal rim and adjusted to a normal internal pressure, with a camber angle of 0° and a normal load applied, and a contact patch half width, which is a distance from the tire equator to a contact edge, which is the outermost end in the tire axial direction, of the contact patch, the contact length includes a crown contact length at the tire equator and a shoulder contact length at a position spaced a distance of 80% of the half contact width from the tire equator, the crown contact length is 0.95 to 1.05 times the shoulder contact length, When a reference virtual groove is defined at the tire equator with a predetermined groove depth, the groove depth d of each of the plurality of grooves satisfies the following formula (1): The groove includes a plurality of circumferential grooves extending in the tire circumferential direction, When the reference imaginary groove, a first imaginary groove set at a first position axially separated from the tire equator, a second imaginary groove set at a second position axially outward of the first position, a third imaginary groove set at a third position axially outward of the second position, and imaginary lines tangent to the groove bottoms of the reference imaginary groove, the groove bottoms of the first imaginary groove, the groove bottoms of the second imaginary groove, and the groove bottoms of the third imaginary groove are defined in a tire meridian cross section in the normal state without load, a groove depth of the circumferential groove is within ±10% of a distance from an outer surface of the tread portion to the virtual line at a position in the tire axial direction where the circumferential groove is formed, A groove depth d1 of the first imaginary groove, a groove depth d2 of the second imaginary groove, and a groove depth d3 of the third imaginary groove are determined based on the following formulas (2) to (4): the circumferential grooves include a crown circumferential groove arranged on or adjacent to the tire equator, and a shoulder circumferential groove arranged axially outward of the crown circumferential groove, a groove depth of the shoulder circumferential groove is greater than a groove depth of the crown circumferential groove, a groove depth of the reference virtual groove is defined based on a groove depth of the crown circumferential groove; tire. [Equation 1] [Equation 2] [Equation 3] [Equation 4] where: d0: groove depth of reference virtual groove LC: Crown contact length L: Contact length at groove position L1: 1st ground contact length L2: 2nd ground contact length L3: 3rd ground contact length α: Correction coefficient

2. The first position is a position separated from the tire equator by a distance of 40% to 55% of the half-contact width, the second position is a position separated from the tire equator by a distance of 75% to 80% of the half contact width, The tire according to claim 1, wherein the third position is a position spaced from the tire equator by a distance of 90% to 85% of the half contact width.

3. A tire as described in claim 1 or 2, wherein the correction coefficient α is a positive number less than or equal to 2.

0.

4. 4. The tire according to claim 3, wherein the correction coefficient α is 0.8 to 1.

2.

5. The tire according to claim 1 , wherein the grooves include a plurality of lateral grooves extending in the tire axial direction.

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