Pneumatic tires

Abstract

The present invention provides a pneumatic tire capable of improving driving stability, noise performance and drainage performance in a balanced manner. A plurality of inner middle lug grooves (13B) are formed on the inner middle land portion (12B), and a plurality of outer middle lug grooves (13D) are formed on the outer middle land portion (12D). The length L1 of the inner middle lug groove (13B) and the length L2 of the outer middle lug groove (13D) satisfy the relationship L1>L2. The distance W1 from the tire equator to the inner shoulder main groove (11A), the distance W2 from the tire equator to the inner central main groove (11B), the distance W3 from the tire equator to the outer central main groove (11C), and the distance W4 from the tire equator to the outer shoulder main groove (11A) are equal to or greater than the distance W5 from the tire equator to the inner shoulder main groove (11A). The distance W4 of the shoulder main groove (11D) relative to the distances Wi and Wo from the tire equator (CL) to the ground contact end satisfies the relationship of 0.58≤W1 / Wi≤0.62, 0.20≤W2 / Wi≤0.24, 0.15≤W3 / Wo≤0.19, and 0.53≤W4 / Wo≤0.57, and the sum of the groove width WG1 of the inner shoulder main groove (11A) and the groove width WG2 of the inner central main groove (11B) is greater than the sum of the groove width WG3 of the outer central main groove (11C) and the groove width WG4 of the outer shoulder main groove (11D).

Description

Technical Field

[0001] The present invention relates to a pneumatic tire having four main grooves in a tread portion, and more particularly to a pneumatic tire capable of improving driving stability, noise performance, and drainage performance in a balanced manner. Background Art

[0002] In pneumatic tires, in order to ensure drainage performance, various schemes have been proposed, such as forming a tread pattern with four main grooves extending along the tire circumference and forming a plurality of transverse grooves in the circumferential land portion divided by these main grooves (for example, refer to patent documents 1 to 3).

[0003] However, while increasing the groove area of the main grooves and lug grooves can improve drainage performance, this can also lead to reduced steering stability and noise performance. Therefore, achieving a high level of balance between steering stability, noise performance, and drainage performance is difficult, and further improvements are desired.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-51834

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2019-1406

[0008] Patent Document 3: Japanese Patent No. 5413500 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] An object of the present invention is to provide a pneumatic tire capable of improving driving stability, noise performance, and drainage performance in a balanced manner.

[0011] Technical means to solve the problem

[0012] The pneumatic tire of the present invention for achieving the above-mentioned object comprises a tread portion extending in the tire circumferential direction and having an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of the sidewall portions, and has an installation direction display portion for indicating the installation direction relative to the vehicle.

[0013] The pneumatic tire is characterized in that the tread portion is formed with four main grooves extending in the tire circumferential direction, the four main grooves including an inner central main groove located on the inner side of the vehicle than the tire equator when installed on a vehicle, an outer central main groove located on the outer side of the vehicle than the tire equator when installed on a vehicle, an inner shoulder main groove located on the inner side of the vehicle than the inner central main groove when installed on a vehicle, and an outer shoulder main groove located on the outer side of the vehicle than the outer central main groove when installed on a vehicle. The main grooves are divided into five rows of land portions, the five rows of land portions including a central land portion divided between the inner central main groove and the outer central main groove, an inner middle land portion divided between the inner central main groove and the inner shoulder main groove, an outer middle land portion divided between the outer central main groove and the outer shoulder main groove, an inner shoulder land portion divided closer to the vehicle inner side than the inner shoulder main groove, and an outer shoulder land portion divided closer to the vehicle outer side than the outer shoulder main groove.

[0014] The inner middle land portion is provided with a plurality of inner middle lug grooves extending in the tire width direction, one end of which is connected to the inner central main groove and the other end of which is terminated in the inner middle land portion. The outer middle land portion is provided with a plurality of outer middle lug grooves extending in the tire width direction, one end of which is connected to the outer shoulder main groove and the other end of which is terminated in the outer middle land portion. The length L1 of the inner middle lug groove and the length L2 of the outer middle lug groove satisfy the relationship L1>L2.

[0015] The distance W1 from the tire equator to the center position of the inner shoulder main groove, the distance W2 from the tire equator to the center position of the inner central main groove, the distance W3 from the tire equator to the center position of the outer central main groove, and the distance W4 from the tire equator to the center position of the outer shoulder main groove satisfy the relationship of 0.58≤W1 / Wi≤0.62, 0.20≤W2 / Wi≤0.24, 0.15≤W3 / Wo≤0.19, and 0.53≤W4 / Wo≤0.57 relative to the distances Wi and Wo from the tire equator to the ground contact ends on the inner and outer sides of the vehicle, and the sum of the groove width WG1 of the inner shoulder main groove and the groove width WG2 of the inner central main groove is greater than the sum of the groove width WG3 of the outer central main groove and the groove width WG4 of the outer shoulder main groove.

[0016] Effects of the Invention

[0017] In the present invention, in a pneumatic tire with a specified mounting orientation relative to a vehicle, by specifying W1 / Wi, W2 / Wi, W3 / Wo, and W4 / Wo as described above and positioning the four main grooves closer to the vehicle's inner side when mounted on the vehicle, it is possible to reduce exterior noise while improving drainage performance. Furthermore, by making the sum of the groove width WG1 of the inner shoulder main groove and the groove width WG2 of the inner center main groove greater than the sum of the groove width WG3 of the outer center main groove and the groove width WG4 of the outer shoulder main groove, drainage performance can be improved without degrading noise performance. Furthermore, in addition to making the sum of the inner shoulder main groove width WG1 and the inner center main groove width WG2 greater than the sum of the outer center main groove width WG3 and the outer shoulder main groove width WG4, the inner middle lug groove length L1 is also made greater than the outer middle lug groove length L2. This allows the tread portion, where greater lateral forces act, to have greater rigidity on the vehicle's outer side than on the vehicle's inner side, thereby improving driving stability on both dry and wet roads. As a result, driving stability, noise reduction, and drainage performance can be further improved.

[0018] In the present invention, the center land portion preferably has a plurality of center lug grooves spaced apart in the tire circumferential direction, extending in the tire width direction, one end communicating with the inner center main groove, and the other end terminating within the center land portion. Providing non-through center lug grooves in the center land portion improves drainage without compromising steering stability.

[0019] It is particularly preferred that the other end of the central lug groove terminates within the central land portion without crossing the tire equator. By arranging the central lug grooves so as not to cross the tire equator, the rigidity of the central land portion can be sufficiently ensured, thereby improving drainage performance without deteriorating steering stability.

[0020] Furthermore, the center land portion preferably has a plurality of center sipes formed at intervals in the tire circumferential direction, extending in the tire width direction, one end communicating with the outer center main groove, and the other end terminating within the center land portion without crossing the tire equator. Arranging the center sipes so as not to cross the tire equator ensures sufficient center land portion rigidity, thereby improving drainage performance without compromising noise performance or steering stability.

[0021] The width Wr1 of the inner middle land portion and the length L1 of the inner middle lug groove preferably satisfy the relationship of 0.6 ≤ L1 / Wr1 ≤ 0.7. The width Wr2 of the outer middle land portion and the length L2 of the outer middle lug groove preferably satisfy the relationship of 0.4 ≤ L2 / Wr2 ≤ 0.5. The width Wr3 of the central land portion and the length L3 of the central lug groove preferably satisfy the relationship of 0.3 ≤ L3 / Wr3 ≤ 0.4. By optimizing the length L1 of the inner middle lug groove, the length L2 of the outer middle lug groove, or the length L3 of the central lug groove, it is possible to achieve balanced improvements in driving stability, noise reduction, and drainage performance.

[0022] The inclination angle θ1 of the acute-angled side of the inner middle lug groove relative to the tire circumferential direction is preferably smaller than the inclination angle θ2 of the acute-angled side of the outer middle lug groove relative to the tire circumferential direction. By making the inclination angle θ1 of the inner middle lug groove smaller than the inclination angle θ2 of the outer middle lug groove, the rigidity of the inner middle land portion can be ensured while maintaining good drainage performance. As a result, steering stability on both dry and wet roads can be balanced.

[0023] The groove walls of the inner shoulder main groove and the outer center main groove on the vehicle's outer side preferably have edges that are chamfered into a serrated shape. By having the groove walls of the inner shoulder main groove and the outer center main groove on the vehicle's outer side have serrated edges, the initial groove area can be maintained without degrading noise performance, thereby improving drainage performance.

[0024] The inner middle lug groove preferably has an inclined portion, where the groove depth gradually decreases from 50% to 65% of the length L1 from its opening end toward the terminal end. The outer middle lug groove preferably has an inclined portion, where the groove depth gradually decreases from 35% to 50% of the length L2 from its opening end toward the terminal end. The central lug groove preferably has an inclined portion, where the groove depth gradually decreases from 25% to 40% of the length L3 from its opening end toward the terminal end. By designing such an inclined portion, the rigidity of each land portion can be avoided, thereby improving drainage performance without compromising steering stability.

[0025] In the present invention, the contact area of the tread portion is determined based on the contact width in the axial direction of the tire, which is measured when the tire rim is assembled on a regular rim and filled with regular internal pressure, and then placed vertically on a plane and a regular load is applied. The contact end is the outermost position of the contact area in the axial direction of the tire. "Regular rim" refers to the rim specified for each tire in the specification system that includes the specifications based on which the tire is based, for example, in the case of JATMA, it is set as a standard rim, in the case of TRA, it is set as a "design rim (Design Rim)", or in the case of ETRTO, it is set as a "measuring rim (Measuring Rim)". "Regular internal pressure" refers to the air pressure corresponding to the maximum load capacity specified for each tire in the specification system that includes the specifications based on which the tire is based. "Regular load" refers to the load equivalent to 80% of the maximum load capacity specified for each tire in the specification system that includes the specifications based on which the tire is based. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention.

[0027] Figure 2 Yes Figure 1 An expanded view of the tread pattern of a pneumatic tire.

[0028] Figure 3 Yes Figure 1 An outline drawing of the tread portion of a pneumatic tire in a meridian section. DETAILED DESCRIPTION

[0029] Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. Figures 1 to 3 1 is a diagram showing a pneumatic tire according to an embodiment of the present invention. This pneumatic tire has designated mounting directions for the front and back of the tire when mounted on a vehicle. Figures 1 to 3 In the figure, inside (IN) refers to the inner side of the vehicle when installed on the vehicle, outside (OUT) refers to the outer side of the vehicle when installed on the vehicle, Ei is the ground terminal on the inner side of the vehicle, Eo is the ground terminal on the outer side of the vehicle, and TCW is the ground connection width.

[0030] like Figure 1As shown, the pneumatic tire of this embodiment includes a tread portion 1 extending in an annular shape in the tire circumferential direction, a pair of sidewall portions 2, 2 disposed on either side of the tread portion 1, and a pair of bead portions 3, 3 disposed radially inward of the sidewall portions 2. For example, an installation direction indicator portion 2A is formed on at least the sidewall portion 2 on the vehicle's outer side to indicate the installation direction relative to the vehicle. The installation direction indicator portion 2A displays, for example, "OUTSIDE" along the tire circumferential direction on the vehicle's outer side and "INSIDE" along the tire circumferential direction on the vehicle's inner side.

[0031] A carcass layer 4 is provided between a pair of bead portions 3, 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and folded back from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. A bead filler 6 composed of a rubber composition and having a triangular cross-section is disposed on the outer periphery of the bead core 5.

[0032] On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 on the tread portion 1. These belt layers 7 are configured to include a plurality of reinforcing cords inclined relative to the tire circumferential direction, and the reinforcing cords cross each other between layers. In the belt layer 7, the inclination angle of the reinforcing cords relative to the tire circumferential direction is set, for example, in the range of 10° to 40°. As the reinforcing cords of the belt layer 7, steel cords are preferably used. In order to improve high-speed durability, at least one belt covering layer 8 is provided on the outer peripheral side of the belt layer 7, in which reinforcing cords are arranged at an angle of, for example, less than 5° relative to the tire circumferential direction. As the reinforcing cords of the belt covering layer 8, organic fiber cords such as nylon and aramid are preferably used.

[0033] It should be noted that the above tire internal structure shows a representative example of a pneumatic tire, but is not limited thereto.

[0034] like Figure 2 As shown, the tread portion 1 has four main grooves 11 extending in the tire circumferential direction. These four main grooves 11 include an inner central main groove 11B located inboard of the tire equator CL when installed on a vehicle; an outer central main groove 11C located outboard of the tire equator CL when installed on a vehicle; an inner shoulder main groove 11A located inboard of the inner central main groove 11B; and an outer shoulder main groove 11D located outboard of the outer central main groove 11C when installed on a vehicle. The main grooves 11 have a groove width within the range of 6.5 mm to 12.0 mm and a groove depth within the range of 6.5 mm to 8.5 mm, and are equipped with wear indicators.

[0035] The tread portion 1 is divided into five rows of land portions 12 by these four main grooves 11. The five rows of land portions 12 include a central land portion 12C defined between the inner central main groove 11B and the outer central main groove 11C, an inner middle land portion 12B defined between the inner central main groove 11B and the inner shoulder main groove 11A, an outer middle land portion 12D defined between the outer central main groove 11C and the outer shoulder main groove 11D, an inner shoulder land portion 12A defined further inboard of the vehicle than the inner shoulder main groove 11A, and an outer shoulder land portion 12E defined further outboard of the vehicle than the outer shoulder main groove 11D.

[0036] The inner shoulder land portion 12A has a plurality of inner shoulder lug grooves 13A formed at intervals in the tire circumferential direction. These grooves extend in the tire width direction, have one end extending further inboard of the vehicle's inner ground contact end Ei, and terminate within the inner shoulder land portion 12A at the other end. Furthermore, the inner shoulder land portion 12A has a plurality of inner shoulder sipes 14A formed at intervals in the tire circumferential direction. These grooves extend in the tire width direction, have one end communicating with the inner shoulder main groove 11A, and terminate within the inner shoulder land portion 12A at the other end.

[0037] The inner middle land portion 12B has a plurality of inner middle lug grooves 13B formed at intervals in the tire circumferential direction. These grooves extend in the tire width direction, one end of which communicates with the inner center main groove 11B and the other end of which terminates within the inner middle land portion 12B. Furthermore, a serrated edge portion 16B is formed on the groove wall of the inner shoulder main groove 11A on the vehicle's outer side (i.e., the sidewall of the inner middle land portion 12B on the vehicle's inner side).

[0038] The center land portion 12C has a plurality of center lug grooves 13C formed at intervals in the tire circumferential direction, extending in the tire width direction, communicating at one end with the inner center main groove 11B, and terminating at the other end within the center land portion 12C. Furthermore, the center land portion 12C has a plurality of center sipes 14C formed at intervals in the tire circumferential direction, extending in the tire width direction, communicating at one end with the outer center main groove 11C, and terminating at the other end within the center land portion 12C.

[0039] The outer middle land portion 12D has a plurality of outer middle lug grooves 13D formed at intervals in the tire circumferential direction. These grooves extend in the tire width direction, one end of which communicates with the outer shoulder main groove 11D and the other end of which terminates within the outer middle land portion 12D. Furthermore, a serrated edge 16D is formed on the groove wall of the outer central main groove 11C on the vehicle's outer side (i.e., the sidewall of the outer middle land portion 12D on the vehicle's inner side).

[0040] The outer shoulder land portion 12E is formed with a plurality of outer shoulder lug grooves 13E spaced apart in the tire circumferential direction. These grooves extend in the tire width direction, one end extending further outboard of the vehicle's outer ground contact end Eo, and the other end terminating within the outer shoulder land portion 12E. A circumferential auxiliary groove 15E is formed in the outer shoulder land portion 12E, extending in the tire circumferential direction and connecting the outer shoulder lug grooves 13E. Furthermore, the outer shoulder land portion 12E is formed with a plurality of outer shoulder sipes 14D spaced apart in the tire circumferential direction. These grooves communicate with the outer shoulder main groove 11D at one end and with the circumferential auxiliary groove 15E at the other end.

[0041] In the pneumatic tire described above, the length L1 of the inner middle lug groove 13B and the length L2 of the outer middle lug groove 13D satisfy the relationship L1 > L2. The lengths L1 and L2 are measured along the tire width direction. By making the length L1 of the inner middle lug groove 13B greater than the length L2 of the outer middle lug groove 13D, the rigidity of the vehicle-outer side portion (outer middle land portion 12D) of the tread portion 1, where greater lateral forces act, can be increased compared to the rigidity of the vehicle-inner side portion (inner middle land portion 12B) of the tread portion 1, thereby improving driving stability on both dry and wet roads.

[0042] In the pneumatic tire described above, the distance W1 from the tire equator CL to the center of the inner shoulder main groove 11A, the distance W2 from the tire equator CL to the center of the inner center main groove 11B, the distance W3 from the tire equator CL to the center of the outer center main groove 11C, and the distance W4 from the tire equator CL to the center of the outer shoulder main groove 11D satisfy the following relationships: 0.58 ≤ W1 / Wi ≤ 0.62, 0.20 ≤ W2 / Wi ≤ 0.24, 0.15 ≤ W3 / Wo ≤ 0.19, and 0.53 ≤ W4 / Wo ≤ 0.57, relative to the distances Wi and Wo from the tire equator CL to the ground contact edges Ei and Eo on the vehicle's inner and outer sides, respectively. Each of the distances Wi and Wo from the tire equator CL to the ground contact edges Ei and Eo on the vehicle's inner and outer sides corresponds to TCW / 2. The center positions of the inner shoulder main groove 11A, the inner center main groove 11B, the outer center main groove 11C, and the outer shoulder main groove 11D are the center positions in the groove width direction, and are the center positions of the groove portions excluding the chamfered portions.

[0043] In a pneumatic tire with a specified mounting orientation relative to a vehicle, by specifying W1 / Wi, W2 / Wi, W3 / Wo, and W4 / Wo as described above and positioning the four main grooves closer to the vehicle's inner side when mounted on the vehicle, it is possible to reduce exterior noise while improving drainage performance. However, if the center positions of the inner shoulder main groove 11A, inner center main groove 11B, outer center main groove 11C, and outer shoulder main groove 11D deviate from the above range, achieving both noise reduction and drainage performance becomes difficult.

[0044] In the above-mentioned pneumatic tire, the sum of the groove width WG1 of the inner shoulder main groove 11A and the groove width WG2 of the inner center main groove 11B (WG1 + WG2) is set to be greater than the sum of the groove width WG3 of the outer center main groove 11C and the groove width WG4 of the outer shoulder main groove 11D (WG3 + WG4). This improves drainage performance without degrading noise performance. Furthermore, by making the sum of the groove width WG1 of the inner shoulder main groove 11A and the groove width WG2 of the inner center main groove 11B greater than the sum of the groove width WG3 of the outer center main groove 11C and the groove width WG4 of the outer shoulder main groove 11D, the rigidity of the vehicle-exterior portion of the tread portion 1, to which greater lateral forces act, can be increased relative to the rigidity of the vehicle-exterior portion of the tread portion 1, thereby improving driving stability on both dry and wet roads. It is particularly desirable to satisfy the relationship WG1 ≥ WG2 > WG3 ≥ WG4.

[0045] In the above-described pneumatic tire, the center land portion 12C preferably has a plurality of center lug grooves 13C formed therein at intervals in the tire circumferential direction, extending in the tire width direction, one end of which communicates with the inner center main groove 11B and the other end of which terminates within the center land portion 12C. Providing non-through center lug grooves 13C in the center land portion 12C in this manner improves drainage performance without impairing steering stability.

[0046] When designing the center lug grooves 13C, it is preferred that the other ends of the center lug grooves 13C terminate within the center land portion 12C, without crossing the tire equator CL. By arranging the center lug grooves 13C so as not to cross the tire equator CL, the rigidity of the center land portion 12C can be sufficiently ensured, thereby improving drainage performance without compromising steering stability.

[0047] In the above-described pneumatic tire, the center land portion 12C preferably has a plurality of center sipes 14C formed therein at intervals in the tire circumferential direction, extending in the tire width direction, one end of the sipes communicating with the outer center main groove 11C, and the other end of the sipes 14C terminating within the center land portion 12C without crossing the tire equator CL. Arranging the center sipes 14C so as not to cross the tire equator CL ensures sufficient rigidity of the center land portion 12C, thereby improving drainage performance without degrading noise performance or steering stability.

[0048] In the above-described pneumatic tire, the width Wr1 of the inner middle land portion 12B and the length L1 of the inner middle lug groove 13B preferably satisfy the relationship 0.6 ≤ L1 / Wr1 ≤ 0.7. By optimizing the length L1 of the inner middle lug groove 13B, it is possible to achieve balanced improvements in steering stability, noise reduction, and drainage performance. If the value of L1 / Wr1 is less than 0.6, the drainage performance improvement effect is reduced. Conversely, if this value is greater than 0.7, the rigidity of the inner middle land portion 12B decreases, which reduces the steering stability improvement effect and the noise reduction effect.

[0049] In the above-described pneumatic tire, the width Wr2 of the outer middle land portion 12D and the length L2 of the outer middle lug groove 13D preferably satisfy the relationship 0.4 ≤ L2 / Wr2 ≤ 0.5. By optimizing the length L2 of the outer middle lug groove 13D, it is possible to achieve balanced improvements in steering stability, noise reduction, and drainage performance. If the value of L2 / Wr2 is less than 0.4, the drainage performance improvement effect is reduced. Conversely, if this value is greater than 0.5, the rigidity of the outer middle land portion 12D decreases, which reduces the steering stability improvement effect and the noise reduction effect.

[0050] In the above-described pneumatic tire, it is preferred that the width Wr3 of the center land portion 12C and the length L3 of the center lug groove 13C satisfy the relationship 0.3 ≤ L3 / Wr3 ≤ 0.4. By optimizing the length L3 of the center lug groove 13C, it is possible to achieve balanced improvements in steering stability, noise reduction, and drainage performance. If the value of L3 / Wr3 is less than 0.3, the drainage performance improvement effect is reduced. Conversely, if this value is greater than 0.4, the rigidity of the center land portion 12C decreases, which reduces the steering stability improvement effect and the noise reduction effect.

[0051] In the above-described pneumatic tire, the inclination angle θ1 of the acute-angled side of the inner middle lug groove 13B relative to the tire circumferential direction is preferably set smaller than the inclination angle θ2 of the acute-angled side of the outer middle lug groove 13D relative to the tire circumferential direction. The inclination angle θ1 is the angle formed by a line connecting the center of the open end and the center of the terminal end of the inner middle lug groove 13B relative to the tire circumferential direction, while the inclination angle θ2 is the angle formed by a line connecting the center of the open end and the center of the terminal end of the outer middle lug groove 13D relative to the tire circumferential direction. By setting the inclination angle θ1 of the inner middle lug groove 13B smaller than the inclination angle θ2 of the outer middle lug groove 13D, the rigidity of the inner middle land portion 12B can be ensured while maintaining good drainage performance. As a result, steering stability on both dry and wet roads can be balanced. It is particularly desirable to set the inclination angle θ1 of the inner middle lug groove 13B within a range of 65° to 71°, and to set the inclination angle θ2 of the outer middle lug groove 13D within a range of 72° to 78°.

[0052] In the above-described pneumatic tire, preferably, the groove walls of the inner shoulder main groove 11A and the outer center main groove 11C on the vehicle's outer side are formed with sawtooth-shaped chamfered edges 16B and 16D, respectively. By providing the groove walls of the inner shoulder main groove 11A and the outer center main groove 11C on the vehicle's outer side with the sawtooth-shaped chamfered edges 16B and 16D, the initial groove area can be secured without degrading noise performance, thereby improving drainage performance.

[0053] In the above-mentioned pneumatic tire, if Figure 3 As shown, the inner middle lug groove 13B, the central lug groove 13C, and the outer middle lug groove 13D have inclined portions 17B, 17C, and 17D, where the groove depth gradually decreases from the middle of their length toward the terminal end. More specifically, the groove depth of the inner middle lug groove 13B gradually decreases toward the terminal end from a distance L1' corresponding to 50% to 65% of the length L1 from the inner middle lug groove 13B's opening end. The groove depth of the outer middle lug groove 13D gradually decreases toward the terminal end from a distance L2' corresponding to 35% to 50% of the length L2 from the outer middle lug groove 13D's opening end. The groove depth of the central lug groove 13C gradually decreases toward the terminal end from a distance L3' corresponding to 25% to 40% of the length L3 from the inner middle lug groove 13B's opening end. By designing these inclined portions 17B, 17C, and 17D, it is possible to avoid reducing the rigidity of the inner middle lug groove 13B, the central lug groove 13C, or the outer middle lug groove 13D, thereby improving drainage performance without compromising steering stability. If the distances L1', L2', and L3' are too small, the improvement in drainage performance will be reduced. Conversely, if they are too large, the improvement in steering stability will be reduced.

[0054] Example

[0055] The following tires of the conventional example, comparative examples 1 to 3, and embodiments 1 to 8 were prepared: In a pneumatic tire having a tire size of 215 / 55R1794V, comprising a tread portion, a pair of sidewall portions, and a pair of bead portions, and having an installation direction display portion indicating the installation direction relative to the vehicle, as shown in FIG. Figure 2 As shown, four main grooves extending in the tire circumferential direction are formed in the tread portion, and five rows of land portions are divided by the four main grooves. Lug grooves and sipes are formed in these land portions.

[0056] In the conventional example, comparative examples 1 to 3, and embodiments 1 to 8, the distances Wi and Wo from the tire equator to the ground contact end, the length L1 of the inner middle lug groove, the length L2 of the outer middle lug groove, the length L3 of the central lug groove, the distance W1 from the tire equator to the center position of the inner shoulder main groove, the distance W2 from the tire equator to the center position of the inner central main groove, the distance W3 from the tire equator to the center position of the outer central main groove, the distance W4 from the tire equator to the center position of the outer shoulder main groove, W1 / Wi, W2 / Wi, W3 / Wo, W4 / Wo, the sum of the groove width WG1 of the inner shoulder main groove and the groove width WG2 of the inner central main groove (WG1+WG2), the groove width WG3 of the outer central main groove and the groove width WG4 of the outer shoulder main groove are calculated. The sum (WG3+WG4), the terminal position of the non-through central lug groove, the presence or absence of a non-through central sipe pattern, the width Wr1 of the inner middle land portion, the width Wr2 of the outer middle land portion, the width Wr3 of the central land portion, L1 / Wr1, L2 / Wr2, L3 / Wr3, the inclination angle θ1 of the inner middle lug groove, the inclination angle θ2 of the outer middle lug groove, whether there are serrated chamfers on the groove walls of the inner shoulder main groove and the outer central main groove on the vehicle outer side, the starting position L1' of the inclined portion of the inner middle lug groove, the starting position L2' of the inclined portion of the outer middle lug groove, the starting position L3' of the inclined portion of the central lug groove, L1' / L1, L2' / L2, L3' / L3 are set as shown in Tables 1 and 2. Note that, regarding the terminal position of the non-through center lug groove, the case where the terminal is on the tire equator is indicated by "A", and the case where the terminal is at a position not crossing the tire equator is indicated by "B".

[0057] The driving stability on a dry road surface and the driving stability on a wet road surface, as well as the noise performance of these test tires were evaluated by the following test methods. The results are shown in Tables 1 and 2.

[0058] Driving stability on dry roads:

[0059] Each test tire was mounted on a 17×7J wheel and attached to a 2500cc passenger car. After preheating, the tires were operated at a pressure (F / R) of 230 kPa / 220 kPa. Sensory evaluations were conducted by test drivers while the tires were driven on dry roads. The evaluation results were expressed as an index, with the conventional tire value set at 100. A higher index value indicates better driving stability on dry roads.

[0060] Driving stability on wet roads:

[0061] Each test tire was mounted on a 17×7J wheel and installed in a 2500cc passenger car. After preheating, the tires were operated at a pressure (F / R) of 230 kPa / 220 kPa. Sensory evaluations were conducted by test drivers while the tires were driven on wet roads. The evaluation results were expressed as an index, with the conventional tire value set at 100. A higher index value indicates better driving stability on wet roads.

[0062] Noise performance:

[0063] Each test tire was mounted on a 17×7J wheel and attached to a 2500cc passenger car. After preheating, the air pressure (F / R) was set to 230kPa / 220kPa. Exterior noise levels were measured in accordance with ECE R117. The reciprocal of the measured value was used to express the evaluation results as an index, with the conventional value set to 100. A higher index value indicates lower exterior noise levels and superior noise performance.

[0064] [Table 1]

[0065]

[0066]

[0067] [Table 2]

[0068]

[0069]

[0070] Tables 1 and 2 show that the tires of Examples 1 to 8 generally exhibit superior driving stability on dry roads, driving stability on wet roads, and noise performance compared to the conventional tires. In contrast, in Comparative Example 1, the inner middle lug groove length L1 is smaller than the outer middle lug groove length L2, resulting in insufficient improvement in driving stability on both dry and wet roads. In Comparative Example 2, the four main grooves are positioned closer to the vehicle's outer sides when installed, resulting in poor noise performance and driving stability on wet roads. In Comparative Example 3, the sum of the inner shoulder main groove width WG1 and the inner center main groove width WG2 (WG1 + WG2) is smaller than the sum of the outer center main groove width WG3 and the outer shoulder main groove width WG4 (WG3 + WG4), resulting in poor noise performance and driving stability on both dry and wet roads.

[0071] Explanation of symbols

[0072] 1: Tread

[0073] 2: Side wall

[0074] 3: Bead

[0075] 11, 11A, 11B, 11C, 11D: Main slots

[0076] 12, 12A, 12B, 12C, 12D, 12E: Coastal area

[0077] 13A, 13B, 13C, 13D, 13E: horizontal grooves

[0078] 14A, 14C, 14E: Sipe

[0079] 15E: Circumferential auxiliary groove

[0080] 16B, 16D: Edge

[0081] 17B, 17C, 17D: inclined portion

Claims

1. A pneumatic tire comprising a tread portion extending in a circumferential direction of the tire and having an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, a pair of bead portions arranged radially inward of the sidewall portions, and a mounting direction indicator portion for indicating a mounting direction relative to a vehicle. The pneumatic tire is characterized in that four main grooves extending in the tire circumferential direction are formed in the tread portion, the four main grooves including an inner central main groove located on the inner side of the vehicle than the tire equator when installed on a vehicle, an outer central main groove located on the outer side of the vehicle than the tire equator when installed on a vehicle, an inner shoulder main groove located on the inner side of the vehicle than the inner central main groove when installed on a vehicle, and an outer shoulder main groove located on the outer side of the vehicle than the outer central main groove when installed on a vehicle. The four main grooves define five rows of land portions, the five rows of land portions including a central land portion defined between the inner central main groove and the outer central main groove, an inner intermediate land portion defined between the inner central main groove and the inner shoulder main groove, an outer intermediate land portion defined between the outer central main groove and the outer shoulder main groove, an inner shoulder land portion defined closer to the vehicle inner side than the inner shoulder main groove, and an outer shoulder land portion defined closer to the vehicle outer side than the outer shoulder main groove. The inner middle land portion is provided with a plurality of inner middle lug grooves extending in the tire width direction, one end of which is connected to the inner central main groove and the other end of which is terminated in the inner middle land portion. The outer middle land portion is provided with a plurality of outer middle lug grooves extending in the tire width direction, one end of which is connected to the outer shoulder main groove and the other end of which is terminated in the outer middle land portion. The length L1 of the inner middle lug groove and the length L2 of the outer middle lug groove satisfy the relationship L1>L2. The distance W1 from the tire equator to the center position of the inner shoulder main groove, the distance W2 from the tire equator to the center position of the inner central main groove, the distance W3 from the tire equator to the center position of the outer central main groove, and the distance W4 from the tire equator to the center position of the outer shoulder main groove satisfy the relationship of 0.58≤W1 / Wi≤0.62, 0.20≤W2 / Wi≤0.24, 0.15≤W3 / Wo≤0.19, and 0.53≤W4 / Wo≤0.57 relative to the distances Wi and Wo from the tire equator to the ground contact ends on the inner and outer sides of the vehicle, and the sum of the groove width WG1 of the inner shoulder main groove and the groove width WG2 of the inner central main groove is greater than the sum of the groove width WG3 of the outer central main groove and the groove width WG4 of the outer shoulder main groove.

2. The pneumatic tire according to claim 1, wherein: The center land portion has a plurality of center lug grooves formed therein at intervals in the tire circumferential direction. The center lug grooves extend in the tire width direction, one end of the lug grooves communicates with the inner center main groove, and the other end of the lug grooves terminates within the center land portion.

3. The pneumatic tire according to claim 2, wherein: The other end of the central lug groove does not cross the tire equator but terminates within the central land portion.

4. The pneumatic tire according to any one of claims 1 to 3, characterized in that: The center land portion has a plurality of center sipes formed thereon at intervals in the tire circumferential direction, extending in the tire width direction, one end communicating with the outer center main groove, and the other end terminating within the center land portion without crossing the tire equator.

5. The pneumatic tire according to any one of claims 1 to 4, characterized in that: The width Wr1 of the inner middle land portion and the length L1 of the inner middle lug groove satisfy the relationship of 0.6≤L1 / Wr1≤0.

7.

6. The pneumatic tire according to any one of claims 1 to 5, characterized in that: The width Wr2 of the outer middle land portion and the length L2 of the outer middle lug groove satisfy the relationship of 0.4≤L2 / Wr2≤0.

5.

7. The pneumatic tire according to claim 2 or 3, characterized in that: The width Wr3 of the central land portion and the length L3 of the central lug groove satisfy the relationship of 0.3≤L3 / Wr3≤0.

4.

8. The pneumatic tire according to any one of claims 1 to 7, characterized in that: An inclination angle θ1 of the acute angle side of the inner middle lug groove with respect to the tire circumferential direction is smaller than an inclination angle θ2 of the acute angle side of the outer middle lug groove with respect to the tire circumferential direction.

9. The pneumatic tire according to any one of claims 1 to 8, characterized in that Groove walls of the inner shoulder main groove and the outer center main groove on the vehicle outer side have edge portions chamfered into a zigzag shape.

10. The pneumatic tire according to any one of claims 1 to 9, characterized in that: The inner middle lug groove has an inclined portion whose groove depth gradually becomes shallower from a position of 50% to 65% of the length L1 with the opening end thereof as a starting point toward the terminal end.

11. The pneumatic tire according to any one of claims 1 to 10, characterized in that: The outer middle lug groove has an inclined portion whose groove depth gradually becomes shallower from a position of 35% to 50% of the length L2 with the opening end thereof as a starting point toward the terminal end.

12. The pneumatic tire according to claim 2, 3 or 7, wherein: The central lug groove has an inclined portion in which the groove depth gradually becomes shallower starting from a position of 25% to 40% of the length L3 with the opening end thereof as a starting point toward the terminal end.

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