tire

Abstract

To improve an anti-hydroplaning performance.SOLUTION: A tire 1 includes a tread part 2. The tread part 2 includes at least one circumferential groove 3 which is recessed and extended from a contact area 2a in a tire circumferential direction. The circumferential groove 3 includes a pair of groove wall parts 8, 8 and a groove bottom part 9. The circumferential groove 3 includes a first circumferential groove 4. In a tire cross section including a tire rotary shaft, the pair of groove wall parts 8A, 8A of the first circumferential groove 4 are substantially orthogonal to virtual profiles P of the contact area 2a to extend from the contact area 2a to an inner side of a tire radial direction. The groove bottom part 9A of the first circumferential groove 4 comes into contact with the pair of groove wall parts 8A, 8A to be a semi-circle 10 protruding toward an inner side of the tire radial direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] Patent Document 1 below describes a tire having a circumferential groove extending in the tire circumferential direction in the tread portion. The groove bottom of the circumferential main groove has an arc portion formed in an arc shape, and the center of the arc of the arc portion is located outside the groove bottom in the tire radial direction. And in the tire of Patent Document 1 below, the ratio of the groove depth of the circumferential groove to the radius of curvature of the arc portion is specified.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, with the improvement of vehicle performance, the opportunity to drive on a wet road surface at high speed has increased. Therefore, it is desired to improve the hydroplaning resistance performance of the tire.

[0005] The present invention has been devised in view of the above actual situation, and the main object thereof is to provide a tire capable of improving the hydroplaning resistance performance.

Means for Solving the Problems

[0006] The present invention is a tire having a tread portion, the tread portion including a ground contact surface and at least one circumferential groove recessed from the ground contact surface and extending in the tire circumferential direction, the at least one circumferential groove including a pair of groove wall portions and a groove bottom portion, the at least one circumferential groove including a first circumferential groove, in a tire cross section including a tire rotation axis, The pair of groove walls of the first circumferential groove extend from the contact surface inward in the tire radial direction, substantially perpendicular to the virtual profile of the contact surface, and The groove bottom is in contact with the pair of groove walls and is a semicircle that is convex inward in the radial direction of the tire. [Effects of the Invention]

[0007] By adopting the above configuration, the tire of the present invention can improve hydroplaning resistance. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view of the tread portion showing one embodiment of the tire of the present invention. [Figure 2] This is a cross-sectional view of the first circumferential groove. [Figure 3] This is a cross-sectional view of the second circumferential groove of this embodiment. [Figure 4] This is a cross-sectional view of a conventional circumferential groove. [Modes for carrying out the invention]

[0009] One embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a plan view of the tread portion 2 of a tire 1 showing one embodiment of the present invention. The tire 1 of the present invention is used, for example, as a pneumatic tire for a passenger car. The present invention may also be used, for example, as a pneumatic tire for heavy loads or motorcycles, or as a non-pneumatic tire that is not filled with compressed air.

[0010] The tread portion 2 includes a contact surface 2a and at least one circumferential groove 3 that is recessed from the contact surface 2a and extends in the circumferential direction of the tire.

[0011] In this embodiment, at least one circumferential groove 3 includes a pair of groove walls 8, 8 and a groove bottom 9. Furthermore, at least one circumferential groove 3 includes a first circumferential groove 4.

[0012] Figure 2 is a cross-section of the tire including the tire rotation axis (not shown), and is an enlarged view of the first circumferential groove 4. Figure 2 is a cross-sectional view of the tire 1 in its normal state. The "normal state" refers to the unloaded state in which the tire 1 is mounted on a normal rim and filled with the normal internal pressure. Unless otherwise specified, the dimensions of each part of the tire 1 are values ​​measured in this normal state.

[0013] "Regular rim" refers to the rim specified for each tire within the standard system on which the tire is based, such as the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO.

[0014] "Regular internal pressure" refers to the air pressure specified for each tire by the aforementioned standards. For JATMA, it means the maximum air pressure; for TRA, it means the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and for ETRTO, it means "INFLATION PRESSURE."

[0015] Figure 4 is a cross-sectional view of a conventional circumferential groove 3. The circumferential groove 3 shown in Figure 4 is formed by a pair of inclined groove walls 8 and a groove bottom 9 connecting the pair of groove walls 8. The groove bottom 9 is formed by an arc 11 with a relatively small radius r. In addition, the circumferential groove 3 has a relatively small cross-sectional area. Furthermore, the length of the arc 11 with respect to the wetted rim is small. For this reason, the circumferential groove 3 in Figure 4 tended to have a small drainage capacity. In contrast, in the first circumferential groove 4 shown in Figure 2, the pair of groove walls 8A of the first circumferential groove 4 extend from the contact surface 2a inward in the tire radial direction, substantially perpendicular to the virtual profile P of the contact surface 2a. In addition, the groove bottom 9A is a semicircle 10 that is tangent to the pair of groove walls 8A and is convex inward in the tire radial direction. In this embodiment, the semicircle 10 is formed by an arc with a single radius r1. This increases the length of the arc portion 11 (semicircle 10) relative to the wetted edge, thereby increasing the drainage volume and improving hydroplaning resistance. Furthermore, such a first circumferential groove 4 has a relatively large cross-sectional area and low drainage resistance at the groove bottom 9A, allowing for a further increase in drainage volume. Therefore, the tire 1 of the present invention can improve hydroplaning resistance by increasing the drainage volume of the first circumferential groove 4. The "cross-sectional area" is the groove area of ​​the cross-section of the circumferential groove 3. The "wetted edge" is the sum of the lengths of the groove wall portion 8 or groove bottom portion 9 that come into contact with water in the circumferential groove 3.

[0016] The contact surface 2a is the surface of the tread portion 2 that makes contact with the flat surface of the tire 1 in its normal state with a normal load applied and a camber angle of 0 degrees. The ends of the contact surface 2a in the tire axial direction are the tread ends Te (shown in Figure 1). The width between the tread ends Te in the tire axial direction is the tread width TW.

[0017] The "normal load" is, in the case of a pneumatic tire, the load defined for each tire in a standard system including the standards on which the tire is based. In the case of JATMA, it is the "maximum load capacity"; in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and in the case of ETRTO, it is the "LOAD CAPACITY".

[0018] The "virtual profile P" refers to the contour shape of the ground contact surface 2a in the normal state in a tire cross-section including the tire rotation axis (not shown). For example, when a chamfer (not shown) is formed at an intersection position K (shown in FIG. 1) between the ground contact surface 2a and the groove wall portion 8A, the virtual profile P refers to a virtual contour shape obtained by filling in this chamfer.

[0019] The term "substantially orthogonal" includes not only the case where the angle α between the groove wall portion 8A and the virtual profile P is 90 degrees, but also the aspect where the angle α is 90 ± 2 degrees. Further, the term "semicircle" includes not only a circle bisected by a diameter, but also an arc having a single radius where a tangent line 10t on one end 10e of the semi-circle 10 overlaps with the groove wall portion 8A.

[0020] As shown in FIG. 1, the tread portion 2 has a crown region Cr having a tire axial width Wc of 44% of the tread width TW centered on the tire equator C, and a pair of shoulder regions Sh adjacent to the crown region Cr on the outer side in the tire axial direction. This crown region Cr is a region with relatively high ground pressure. Therefore, it is considered that the circumferential grooves 3 arranged in this crown region Cr contribute greatly to the hydroplaning resistance performance as compared with the circumferential grooves 3 arranged in the shoulder regions Sh.

[0021] At least one circumferential groove 3 includes a plurality of circumferential grooves 3. The plurality of circumferential grooves 3 includes a first circumferential groove 4 arranged closest to the tire equator C and at least one second circumferential groove 5 arranged outside the first circumferential groove 4 in the tire axial direction. The circumferential groove 3 of the present embodiment includes a pair of first circumferential grooves 4 arranged on both sides of the tire equator C and a pair of second circumferential grooves 5 arranged outside the first circumferential groove 4 in the tire axial direction. Thus, the first circumferential groove 4 provided at a position adjacent to the tire equator C helps to further improve the hydroplaning resistance performance. Note that the circumferential groove 3 is not limited to such a mode. For example, it may include two second circumferential grooves 5 outside the first circumferential groove 4 in the tire axial direction.

[0022] Also, the first circumferential groove 4 is preferably arranged in the crown region Cr. Thereby, the hydroplaning resistance performance can be further improved. In the present embodiment, the groove width center line 4c of the first circumferential groove 4 is arranged in the crown region Cr. Also, for example, the outer end 4e of the first circumferential groove 4 in the tire axial direction is arranged in the crown region Cr. Note that three or more first circumferential grooves 4 may be provided in the crown region Cr.

[0023] As shown in Figure 2, the groove width W1 of the first circumferential groove 4 is preferably 8 mm or more, and the radius r1 of the semicircle 10 is preferably 4 mm or more. Since the groove width W1 is 8 mm or more, the cross-sectional area A1 of the first circumferential groove 4 can be kept large. Since the radius r1 is 4 mm or more, the drainage resistance at the groove bottom 9 can be reduced. If the groove width W1 or radius r1 is excessively large, the cross-sectional area A1 (shown in Figure 2(B)) will become too large, and there is a risk that the noise generated from the first circumferential groove 4 will become excessively large. For this reason, in the case of a passenger car tire 1, the groove width W1 is more preferably 9 mm or more, preferably 13 mm or less, and more preferably 12 mm or less. Also, the radius r1 is more preferably 4.5 mm or more, preferably 6.5 mm or less, and more preferably 6 mm or less. Furthermore, the ratio of the length La of the groove bottom 9 to the maximum value Lb of the wetted perimeter (La / Lb) is preferably 60% or more. The length La in the first circumferential groove 4 shown in Figure 2 is 2 × π × r1 × (180 degrees / 360 degrees) = π × r1. The maximum value Lb is the sum of the lengths of the inner groove wall portion 8 and the groove bottom portion 9 in the radial direction of the tire from the contact surface 2a, and in the first circumferential groove 4 shown in Figure 2, it is H1 × 2 + π × r1.

[0024] The length H1 of each of the pair of groove walls 8A, 8A of the first circumferential groove 4 in the tire radial direction is preferably 50% or less of the maximum depth D1 of the first circumferential groove 4, and more preferably 40% or less. This allows for a smaller wetted perimeter when the cross-sectional area A1 of the first circumferential groove 4, whose groove bottom 9 is semicircular, is kept the same size. Reducing the wetted perimeter is thought to reduce drainage resistance and increase flow velocity, thereby improving hydroplaning resistance. From this viewpoint, it is preferable that the groove width W1 of the first circumferential groove 4 is greater than or equal to the maximum depth D1 of the first circumferential groove 4.

[0025] As shown in Figure 1, the second circumferential groove 5 in this embodiment is located in the shoulder region Sh. In this embodiment, the groove width centerline 5c of the second circumferential groove 5 is located in the shoulder region Sh. Also, for example, the inner end 5i of the second circumferential groove 5 in the tire axial direction is located in the shoulder region Sh.

[0026] Figure 3 is a cross-section of a tire including the tire rotation axis (not shown), and is an enlarged view of the second circumferential groove 5. As shown in Figure 3, the groove bottom 9B of the second circumferential groove 5 in this embodiment includes a pair of arc portions 11. The radius of curvature r2 of the pair of arc portions 11 is smaller than the radius r1 of the semicircle 10 of the groove bottom 9A of the first circumferential groove 4. Such a second circumferential groove 5 provides appropriate flexibility to the tread portion 2 near the second circumferential groove 5, mitigating the impact when the tire makes contact with the ground, thereby improving noise performance.

[0027] In this embodiment, the pair of arc portions 11 of the groove bottom portion 9B are smoothly connected to, for example, each groove wall portion 8B. In this embodiment, the groove wall portion 8B is inclined with respect to the virtual profile P of the contact surface 2a. The "inclination" refers to a configuration in which the angle α between the groove wall portion 8A and the virtual profile P is greater than 92 degrees. Although not particularly limited, the angle α of the second circumferential groove 5 is preferably 105 degrees or less, and preferably 100 degrees or less.

[0028] Furthermore, the groove bottom 9B of the second circumferential groove 5 includes a joint 12 connecting a pair of arc sections 11. The joint 12 extends parallel to the contact surface 2a in the tire cross-section including the tire rotation axis and intersects with the groove width centerline 5c. The joint 12 is not limited to this configuration and may be formed, for example, by an arc with a larger radius of curvature than the arc section 11.

[0029] To improve noise performance, the radius of curvature r2 of the arc portion 11 of the second circumferential groove 5 is preferably 50% or less of the radius r1 of the semicircle 10 of the first circumferential groove 4, and more preferably 30% or less. Although not particularly limited, the radius of curvature r2 of the arc portion 11 is preferably 1 mm or more, and more preferably 1.5 mm or more.

[0030] The cross-sectional area A2 of the second circumferential groove 5 is preferably 60% or more of the cross-sectional area A1 of the first circumferential groove 4, more preferably 65% ​​or more, preferably 80% or less, and more preferably 75% or less. Since the cross-sectional area A2 is 60% or more of the cross-sectional area A1, high hydroplaning resistance is maintained. Since the cross-sectional area A2 is 80% or less of the cross-sectional area A1, the noise performance improvement effect of the second circumferential groove 5 is realized.

[0031] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiments described above and can be implemented in various modified forms. [Examples]

[0032] A prototype tire with the basic pattern shown in Figure 1 was manufactured based on the specifications in Table 1. The hydroplaning resistance and noise performance of each test tire were then tested. The common specifications and test methods for each test tire are as follows. Tire size: 215 / 55R17 Rim: 17×7.5J Internal pressure: 230kPa Radius of curvature r2 of the arc portion in the embodiment: 1 mm The circumferential grooves in the shoulder region of the comparative example and the circumferential grooves in the shoulder region of the embodiment are similar in shape.

[0033] <Hydroplaning resistance> Using a well-known inside drum testing machine, the braking force and travel speed were measured when a test tire was driven on a water-sprayed drum surface. Specifically, the maximum braking force when the drum's speed was increased at a constant acceleration, and the travel speed at which the braking force reached 50% of the maximum braking force (referred to as the "hydroplaning initiation speed") were measured. The results are shown as an index with the hydroplaning initiation speed of Comparative Example 1 set to 100. A higher value indicates better hydroplaning resistance. Vertical load: 4.2kN Maximum water depth: 5mm

[0034] <Noise performance> Using a well-known outside drum testing machine, the total sound pressure (decibels) of the running noise (100-2000 Hz) when a test tire was run on the drum surface was measured using a sound-collecting microphone. The results are shown as a difference from the comparative example. Vertical load: 4.2kN Slip angle: 0 degrees Test tire speed: 50 km / h The test results are shown in Table 1.

[0035] [Table 1]

[0036] The test results showed that the example tire had equivalent hydroplaning resistance to the comparative example tire, despite having a 7% smaller total cross-sectional area of ​​circumferential grooves. Furthermore, because the example tire has circumferential grooves shown in Figure 2 in the crown region, noise performance can be improved compared to the comparative example tire even if circumferential grooves with a smaller cross-sectional area, as shown in Figure 3, are placed in the shoulder region. Thus, the example tire can improve both hydroplaning resistance and noise performance.

[0037] [Note] The present invention includes the following embodiments.

[0038] [Invention 1] A tire having a tread portion, The tread portion includes a contact surface and at least one circumferential groove that is recessed from the contact surface and extends in the circumferential direction of the tire. The at least one circumferential groove includes a pair of groove walls and a groove bottom, The at least one circumferential groove includes a first circumferential groove, In the tire cross-section including the tire rotation axis, The pair of groove walls of the first circumferential groove extend from the contact surface inward in the tire radial direction, substantially perpendicular to the virtual profile of the contact surface, and The groove bottom is in contact with the pair of groove walls and is a semicircle that is convex inward in the radial direction of the tire. tire. [Invention 2] The tire according to the present invention, wherein the groove width of the first circumferential groove is 8 mm or more, and the radius of the semicircle is 4 mm or more. [Invention 3] The tire according to invention 1 or 2, wherein the length of each of the pair of groove walls of the first circumferential groove in the tire radial direction is 50% or less of the maximum depth of the first circumferential groove. [4th Invention] The aforementioned at least one circumferential groove includes a plurality of circumferential grooves, The plurality of circumferential grooves include a first circumferential groove located closest to the tire equator, and at least one second circumferential groove located further outward in the tire axial direction than the first circumferential groove. In the tire cross-section including the tire rotation axis, The bottom of the second circumferential groove includes a pair of arc portions, The tire according to invention 1 or 2, wherein the radius of curvature of the pair of arc portions is smaller than the radius of the semicircle at the bottom of the groove of the first circumferential groove. [5th ​​Invention] The tire according to the present invention, wherein the cross-sectional area of ​​the second circumferential groove is 60% to 80% of the cross-sectional area of ​​the first circumferential groove. [Explanation of symbols]

[0039] 1 tire 2 Tread section 2a Ground plane 3 Circumferential groove 4 First circumferential groove 8, 8A groove wall 9, 9A groove bottom 10 semicircles P Virtual Profile

Claims

1. A tire having a tread portion, The tread portion includes a contact surface and at least one circumferential groove that is recessed from the contact surface and extends in the circumferential direction of the tire. The at least one circumferential groove includes a pair of groove walls and a groove bottom, The at least one circumferential groove includes a first circumferential groove, In the tire cross-section including the tire rotation axis, The pair of groove walls of the first circumferential groove extend from the contact surface inward in the tire radial direction, substantially perpendicular to the virtual profile of the contact surface, and The groove bottom is in contact with the pair of groove walls and is a semicircle that is convex inward in the tire radial direction. The length of each of the pair of groove walls of the first circumferential groove in the tire radial direction is 50% or less of the maximum depth of the first circumferential groove. tire.

2. The tire according to claim 1, wherein the groove width of the first circumferential groove is 8 mm or more, and the radius of the semicircle is 4 mm or more.

3. A tire having a tread portion, The tread portion includes a contact surface and at least one circumferential groove that is recessed from the contact surface and extends in the circumferential direction of the tire. The at least one circumferential groove includes a pair of groove walls and a groove bottom, The at least one circumferential groove includes a first circumferential groove, In the tire cross-section including the tire rotation axis, The pair of groove walls of the first circumferential groove extend from the contact surface inward in the tire radial direction, substantially perpendicular to the virtual profile of the contact surface, and The groove bottom is in contact with the pair of groove walls and is a semicircle that is convex inward in the tire radial direction. The aforementioned at least one circumferential groove includes a plurality of circumferential grooves, The plurality of circumferential grooves include a first circumferential groove located closest to the tire equator, and at least one second circumferential groove located further outward in the tire axial direction than the first circumferential groove. In the tire cross-section including the tire rotation axis, The bottom of the second circumferential groove includes a pair of arc portions, The radius of curvature of the pair of circular arcs is smaller than the radius of the semicircle at the bottom of the first circumferential groove. tire.

4. The tire according to claim 3, wherein the cross-sectional area of ​​the second circumferential groove is 60% to 80% of the cross-sectional area of ​​the first circumferential groove.

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