pneumatic tires

Abstract

To provide a pneumatic tire that can make both reduction in a maximum value of cornering force and reduction of tire noise compatible.SOLUTION: A tire 1 that is one example of embodiments includes a tread 10 which has a center land part 40 including a center in a tire width direction, mediate land parts 44 provided through first circumferential main grooves 20 at both sides in a tire width direction of the center land part 40 and shoulder land parts 50 provided through second circumferential main grooves 21, outsides in the tire width direction of the mediate land parts 44. The mediate land parts 44 are formed with circumferential sub grooves 46 which are smaller in width than the circumferential main grooves 20 and 21 and extend in a tire circumferential direction. In the mediate land part 44, a taper-shaped chamfer 47 is formed at an opening end of a wall surface forming at least either of the first circumferential main groove 20 and the second circumferential main groove 21.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a tread including a plurality of land portions. [Background technology]

[0002] Conventionally, a pneumatic tire has been described in which the length (width) of a middle land portion in the tire width direction is made larger than the width of a center land portion, thereby increasing the upper limit of the slip angle during running and thereby increasing cornering power (see Patent Document 1). Patent Document 1 also describes forming a middle thin groove in the middle land portion that is narrower in width than the other circumferential grooves and extends in the circumferential direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-227007 Summary of the Invention [Problem to be solved by the invention]

[0004] In the pneumatic tire of Patent Document 1, it is conceivable to reduce the maximum cornering force (CFmax) by increasing the tire widthwise length (width) of the circumferential main groove adjacent to the middle land portion in the tire width direction. This reduces the tire widthwise length of the middle land portion. By reducing CFmax, the increase in grip force during cornering, which increases the slip angle, can be suppressed. Therefore, even when used in tall vehicles such as minivans, minivans, and box-type vehicles like buses, the outward roll of the vehicle during cornering can be suppressed. However, simply increasing the width of the circumferential main groove increases the volume of the circumferential main groove, which increases tire noise (pneumatic pipe resonance). Therefore, it is desirable to achieve both a decrease in CFmax and a reduction in tire noise.

[0005] An object of the present invention is to provide a pneumatic tire that can achieve both a reduction in maximum cornering force and a reduction in tire noise. [Means for solving the problem]

[0006] The pneumatic tire of the present invention is a pneumatic tire having a tread including a center land portion including the center in the tire width direction, intermediate land portions provided on both sides of the center land portion in the tire width direction via first circumferential main grooves, and shoulder land portions provided on the tire width direction outer sides of each of the two intermediate land portions via second circumferential main grooves, wherein the intermediate land portion has a circumferential sub-groove formed therein that is smaller than the width of the first circumferential main groove and the second circumferential main groove and extends in the tire circumferential direction, and the intermediate land portion has a tapered chamfer formed at the open end of a wall surface that forms at least one of the first circumferential main groove and the second circumferential main groove. [Effects of the Invention]

[0007] According to the pneumatic tire of the present invention, the volume of at least one of the first circumferential main groove and the second circumferential main groove between the intermediate land portion and the adjacent land portion can be reduced while reducing the tire contact area, thereby achieving both a reduction in the maximum cornering force and a reduction in tire noise (pneumatic pipe resonance). [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a pneumatic tire as an example of an embodiment. [Figure 2] FIG. 2 is a plan view of a portion of the tread shown in FIG. 1 in the circumferential direction. [Figure 3] FIG. 2 is an enlarged view of part A in FIG. [Figure 4] FIG. 4 is an enlarged view of part B in FIG. 3. [Figure 5] FIG. 3 is an image diagram showing the contact area of ​​the vehicle in FIG. 2 when the vehicle is turning. [Figure 6]FIG. 2 is a diagram showing the relationship between cornering force (CF) and slip angle (SA) as viewed from above the tire. [Figure 7] FIG. 2 is a diagram showing an example of the relationship between cornering force (CF) and slip angle (SA). DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes selective combinations of the components of the multiple embodiments and modified examples described below.

[0010] FIG. 1 is a cross-sectional view of a pneumatic tire 1 according to an embodiment. FIG. 2 is a plan view of a circumferential portion of a tread 10 shown in FIG. 1. FIG. 3 is an enlarged view of part A in FIG. 1, and FIG. 4 is an enlarged view of part B in FIG. 3. As shown in FIGS. 1 and 2, the pneumatic tire 1 includes a tread 10 that is a portion that comes into contact with the road surface. Hereinafter, the "pneumatic tire 1" will be referred to as the "tire 1." The tread 10 has a tread pattern that includes a plurality of land portions, and is formed in an annular shape along the circumferential direction of the tire.

[0011] The following description focuses on the portion of the tire 1 that is on the vehicle inner side (IN side) when mounted on a vehicle, centered on the tire width center CL, as the configuration of the tire 1. The outer shape of the tire 1 is symmetrical between the portion on the vehicle inner side and the portion on the vehicle outer side (OUT side) centered on the tire width center CL, except for the lug grooves and sipes described below.

[0012] The tread 10 includes land portions 40, 44, and 50 defined by, for example, four circumferential main grooves 20 and 21. The land portions 40, 44, and 50 are protrusions that protrude radially outward from the reference plane of the tread 10. The "reference plane" refers to a virtual plane along the bottom surfaces of the deepest circumferential main grooves 20 and 21, and refers to the outer peripheral surface of the tread 10 in the absence of any land portions. The tread 10 includes, by the four circumferential main grooves 20 and 21, the following land portions: a center land portion 40 including the center CL in the tire width direction; intermediate land portions 44 provided on both sides of the center land portion 40 in the tire width direction via first circumferential main grooves 20; and shoulder land portions 50 provided on the tire width direction outer sides of each of the two intermediate land portions 44 via second circumferential main grooves 21.

[0013] Each of the center land portion 40, the two intermediate land portions 44, and the two shoulder land portions 50 has a rib shape that is continuous around the entire circumference of the tire.

[0014] The tire 1 includes a sidewall 12 that is provided on the outer side of the tread 10 in the tire width direction and bulges outward most in the tire width direction, and a bead (not shown) that is fixed to the rim of a wheel. The sidewall 12 and the bead are formed in an annular shape along the tire circumferential direction and constitute a tire side surface 13. The sidewall 12 extends radially inward from both ends of the tread 10 in the tire width direction.

[0015] The tire 1 is a pneumatic tire that is filled with air at a predetermined pressure. The tread 10 and the sidewall 12 are made of, for example, different types of rubber.

[0016] The shoulder land portions 50 arranged at both widthwise ends of the tread 10 include a ground contact edge T (Figure 2), which is the outer edge of the ground contact surface in the tire width direction. The tire widthwise end of each shoulder land portion 50 extends outward in the tire width direction from the ground contact edge T, and is gently curved radially inward in the tire radial direction so that the outer peripheral surface is convex outward. The portion of each shoulder land portion 50 extending outward in the tire width direction from the ground contact edge T is called a buttress.

[0017] "Ground contact edge T" means both ends in the tire width direction of the area that comes into contact with a flat road surface when an unused tire 1 is mounted on a standard rim and inflated to the standard internal pressure, and a load of 70% of the standard load at the standard internal pressure is applied.

[0018] Here, a "regular rim" is a rim specified by the tire standard, and is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO.

[0019] Although not shown, the tire 1 includes a carcass, a belt, and an inner liner. The carcass is a cord layer coated with rubber and forms the framework of the tire 1, which can withstand loads, impacts, air pressure, etc. The belt is a reinforcing band placed between the carcass and the rubber that makes up the tread 10. The belt tightly tightens the carcass, increasing the rigidity of the tire 1. The inner liner is a rubber layer provided on the inner surface of the carcass and maintains the air pressure of the tire 1. The bead includes a bead core and a bead filler.

[0020] A plurality of lug grooves 60 are formed extending substantially in the tire width direction at a plurality of positions in the tire circumferential direction of each shoulder land portion 50. The inner end of each lug groove 60 in the tire width direction terminates within the shoulder land portion 50 and does not open to the wall surface of the shoulder land portion 50. Forming such lug grooves 60 improves drainage toward the outside in the tire width direction.

[0021] A plurality of thin sipes 91, 80, 81 extending substantially in the tire width direction or in a direction inclined relative to the tire width direction are formed on the contact surface of each land portion 40, 44, 50. In Fig. 2, the position of each sipe 91, 80, 81 is schematically indicated by a dashed line. Each sipe 91, 80, 81 is a thin groove that is narrower than each circumferential main groove 20, 21, the circumferential sub-groove 46 (described later), and the lug groove 60. The sipes 91, 80, 81 enhance the edge effect that grips snow and ice, thereby achieving good braking / driving performance and handling stability on snowy and icy roads.

[0022] 2, sipes 80, 81 formed in each shoulder land portion 50 have first straight portions 82, 84 located on the outer side in the tire width direction and extending substantially in the tire width direction, and second straight portions 83, 85 connected to the inner ends of the first straight portions 82, 84 in the tire width direction and extending in a direction inclined relative to the tire width direction. One end of the second straight portions 83, 85 opens into the second circumferential main groove 21. Each intermediate land portion 44 and center land portion 40 has a substantially straight sipe 91 formed therein, extending in a direction inclined toward one side in the tire width direction and substantially toward the same side in the tire circumferential direction.

[0023] Furthermore, each intermediate land portion 44 is formed with a circumferential sub-groove 46 that is smaller in width than each of the first circumferential main grooves 20 and each of the second circumferential main grooves 21 and extends in the tire circumferential direction. The circumferential sub-groove 46 is formed, for example, in the ground contact surface of each intermediate land portion 44 so as to be recessed in the tire radial direction at approximately the center in the tire width direction. The tire radial depth d1 (FIG. 3) of each circumferential sub-groove 46 at the tire width center is smaller than the tire radial depths d2, d3 (FIG. 3) of each of the first circumferential main grooves 20 and each of the second circumferential main grooves 21 at the tire width center. By forming the circumferential sub-groove 46 in this way in the intermediate land portion 44, the ground contact area of ​​the intermediate land portion 44 can be reduced by the amount of the circumferential sub-groove 46. This allows the maximum value CFmax of cornering force CF to be reduced, as described below.

[0024] Furthermore, in each intermediate land portion 44, a tapered chamfer 47 is formed at the tire radially outer open end of the wall surface 45 that forms at least one of the first circumferential main groove 20 and the second circumferential main groove 21. The chamfer 47 is formed on the outer side of the wall surface 45 of each intermediate land portion 44 over the entire tire circumferential length. The angle of inclination of the chamfer 47 with respect to the tire radial direction is greater than the angle of inclination of the portion of the wall surface 45 on which the chamfer 47 is formed, located on the groove bottom side of the chamfer 47, with respect to the tire radial direction. The tire radial depth d4 of the chamfer 47 ( FIG. 4 ) is smaller than the tire radial depth d1 of each circumferential sub-groove 46. As described below, this, combined with the effect of forming the circumferential sub-groove 46, enables both a reduction in CFmax and tire noise to be achieved.

[0025] In FIG. 3, the wall surfaces of each circumferential main groove 20, 21, excluding the chamfer 47, are also inclined relative to the tire radial direction, but the wall surfaces of at least one of the circumferential main grooves 20, 21, excluding the chamfer, may be shaped along the tire radial direction.

[0026] In Figures 2 and 3, in each intermediate land portion 44, a chamfer 47 is formed on the outside of the wall surface 45 that forms the second circumferential main groove 21, but in each intermediate land portion 44, a tapered chamfer may be formed at the opening end of the wall surface that forms the first circumferential main groove 20, instead of or in addition to the wall surface that forms the second circumferential main groove 21.

[0027] According to the tire 1 described above, a circumferential sub-groove 46 is formed in the intermediate land portion 44, and a tapered chamfer 47 is formed at the open end of the wall surface of the intermediate land portion 44 that forms at least one of the first circumferential main groove 20 and the second circumferential main groove 21. This reduces the ground contact area of ​​the tire 1, while also reducing the volume of the circumferential main groove between the intermediate land portion 44 and another adjacent land portion, which is at least one of the first circumferential main groove 20 and the second circumferential main groove 21, for example, the second circumferential main groove 21.

[0028] For example, as shown by the two-dot chain line α in FIG. 3 , instead of forming a chamfer at the end of the intermediate land portion 44 on the second circumferential main groove 21 side, it is possible to shift the wall surface 48 of the second circumferential main groove 21 forming the intermediate land portion 44 toward the tire width direction center (the right side in FIG. 3 ) so that the opening coincides with the tire radially outer end of the chamfer. In this case, the distance between the wall surfaces 49, 48 on both sides of the second circumferential main groove 21 in the tire width direction becomes larger. In this case, as in the embodiment in which the chamfer 47 is formed on the second circumferential main groove 21 side of the intermediate land portion 44, the contact area of ​​the intermediate land portion 44 can be reduced. This may reduce the CFmax. However, in this case, the distance between the wall surfaces 49, 48 of the second circumferential main groove 21 becomes larger, which increases the volume of the second circumferential main groove 21. This increases tire noise, i.e., air-tight resonance noise.

[0029] In the embodiment, a tapered chamfer 47 is formed on the second circumferential main groove 21 side of the intermediate land portion 44. This reduces the contact area of ​​the intermediate land portion 44 and reduces CFmax without increasing the distance between the wall surfaces 49, 45 on both sides of the second circumferential main groove 21 in the tire width direction. That is, since CFmax can be reduced without increasing the volume of the second circumferential main groove 21, both a reduction in CFmax and tire noise can be achieved. Furthermore, because the chamfer 47 is tapered, compared to a case in which the chamfer 47 has a curved arc cross section, the contact area of ​​the intermediate land portion 44 is prevented from expanding significantly when the tire 1 contact pressure increases. This allows CFmax to be reduced regardless of the tire 1 contact pressure. Therefore, even when the tire of the embodiment is used on vehicles with a large vehicle height, such as minivans and box-shaped vehicles, excessively high grip force can be prevented, thereby suppressing outward vehicle roll during cornering. Generally, when a vehicle has an aspect ratio, i.e., a ratio (H / W) of vehicle height (catalog value) H to vehicle width (catalog value) W of 1 or more, the vehicle is more likely to roll to the outside of a turn than a vehicle with an aspect ratio of less than 1. For this reason, the effect of suppressing vehicle roll by reducing CFmax using a configuration in which a circumferential sub-groove is formed in the mediate land portion, as in the embodiment, becomes significant when the aspect ratio is 1 or more.

[0030] In FIG. 3, even when a chamfer is formed on the outer side of the wall surface forming the first circumferential main groove 20 in the intermediate land portion 44 instead of the wall surface forming the second circumferential main groove 21, it is possible to achieve both a reduction in CFmax and a reduction in tire noise, similar to the case where a chamfer 47 is formed on the outer side of the wall surface forming the second circumferential main groove 21.

[0031] Furthermore, in the intermediate land portion 44, if chamfers are formed on the wall surfaces forming the first circumferential main groove 20 as well as the wall surfaces forming the second circumferential main groove 21, the volumes of both the first and second circumferential main grooves 21 can be reduced, thereby achieving a higher level of both a reduction in CFmax and a reduction in tire noise.

[0032] For example, if the tire 1 has a tire section width of 225 mm, a ratio of the tire section height to the tire section width of 60%, and a wheel rim outer diameter of 18 inches, the dimension (width) of the circumferential sub-groove 46 in the tire width direction is preferably 1 to 3 mm, and more preferably approximately 1.5 mm. If the width of the circumferential sub-groove 46 is less than 1 mm, the effect of reducing CFmax due to the reduction in the contact area of ​​the intermediate land portion 44 will be reduced. On the other hand, if the width of the circumferential sub-groove 46 exceeds 3 mm, the effect of reducing tire noise will be reduced.

[0033] Under the above tire conditions, the depth d1 of the circumferential sub groove 46 in the tire radial direction is preferably about 3 mm. Under the above tire conditions, the dimension of the chamfer 47 in the tire width direction is preferably about 1 mm, and the depth in the tire radial direction is preferably about 1 mm.

[0034] The effect of reducing CFmax according to the embodiment will be described below. Fig. 5 is an image diagram showing an example of the contact patches 86-90 when the vehicle is turning in Fig. 2. In Fig. 5, the slip angle (SA) of the tire 1 is about 8-10 degrees.

[0035] Here, SA is the angle between the tire's forward direction (arrow P), which coincides with the vehicle's forward direction when the vehicle's steering wheel is operated, and the tire's longitudinal direction (dashed line Q), which passes through the tire's center in the tire's width direction, as shown in Figure 6. When viewed from above, the point of application of the cornering force (CF) is located at a position that is pneumatic trail dN rearward from the center C of the tire's contact point. A drag force (DF) acts on the tire 1 in the rearward direction, perpendicular to CF. The resultant force F of CF and DF can be separated into two perpendicular components: a side force SF, which is a lateral force, and rolling resistance R between the tire 1 and the ground. A vehicle can turn when the lateral force, which approximates CF, is balanced with the centrifugal force.

[0036] An example of the relationship between CF and SA is shown in Figure 7. As shown in Figure 7, CF increases as SA increases, and normally, CF reaches its maximum value, CFmax, when SA is around 8 to 10 degrees, as shown in Figure 5.

[0037] In the embodiment, the formation of the circumferential sub-groove 46 as described above reduces the contact area of ​​the intermediate land portion 44, thereby increasing the average contact pressure on the contact surface. Meanwhile, CFmax is calculated by the following formula, where μ is the lateral friction coefficient acting between the tire 1 and the ground, and N is the vertical load acting on the contact portion of the tire 1. CFmax=μ×N (1)

[0038] In addition, the friction coefficient μ of rubber is pressure-dependent, and the friction coefficient μ decreases as the ground contact pressure increases. Therefore, when the ground contact pressure of the tire 1 increases as in the embodiment, CFmax decreases when the normal load N acting on the tire 1 remains the same.

[0039] 5, when SA is around 8 to 10 degrees, where CFmax is maximized, the area of ​​the ground contact patch 86 in the shoulder land portion 50 on the inside of the turn (left side of FIG. 5) is significantly smaller. For this reason, it can be seen that forming the circumferential sub-groove 46 in the intermediate land portion 44 as in the embodiment is easier to achieve the desired effect regardless of the turning direction of the tire than forming a circumferential sub-groove in the shoulder land portion 50. Furthermore, of the two intermediate land portions 44 on both sides of the turn, the intermediate land portion 44 on the outside of the turn (right side of FIG. 5) is more effective in reducing CFmax due to the reduction in the ground contact area achieved by forming the circumferential sub-groove 46.

[0040] Next, the results of a simulation conducted by the inventor to confirm the effects of the present invention will be described. In the simulation, CFmax and tire noise were calculated using an example tire having a configuration similar to that of the embodiment, and tires of comparative examples 1 and 2. In comparative example 1, no circumferential sub-grooves are formed in the land portions 40, 44, and 50, and no tapered chamfers are formed at the tire width direction ends of the land portions 40, 44, and 50. The other configurations are the same as those of the examples. In comparative example 2, compared to comparative example 1, circumferential sub-grooves 46 are formed in each intermediate land portion 44, similar to those of the examples.

[0041] Table 1 shows the simulation results of CFmax and tire noise in the Example, Comparative Example 1, and Comparative Example 2. In the simulation results in Table 1, the values ​​for Comparative Example 2 and the Example are shown as relative values ​​when the CFmax and tire noise in Comparative Example 1 are each set to a reference value of 100.

[0042] [Table 1]

[0043] From the simulation results in Table 1, when the circumferential sub-groove 46 is formed in the intermediate land portion 44 as in Comparative Example 2, the ground contact area of ​​the intermediate land portion 44 can be reduced, and CFmax can be reduced more than in Comparative Example 1. On the other hand, in Comparative Example 2, tire noise increases slightly due to the formation of the circumferential sub-groove 46.

[0044] On the other hand, in the case of the example, in addition to the circumferential sub-groove 46 being formed in the intermediate land portion 44, a tapered chamfer is formed at the end of the intermediate land portion 44 on the side of the second circumferential main groove 21. This reduces CFmax in the same manner as in Comparative Example 1, while reducing the volume of the second circumferential main groove 21, thereby reducing tire noise.

[0045] In the above embodiment, the center land portion 40, the intermediate land portion 44, and the shoulder land portion 50 are each described as having a rib shape that is continuous around the entire circumference of the tire and is not divided in the tire circumferential direction by lug grooves. However, each land portion may be configured as a plurality of blocks that are divided in the tire circumferential direction by a plurality of lug grooves extending from a first side to a second side in the tire width direction. [Explanation of symbols]

[0046] 1 tire, 10 tread, 12 sidewall, 13 tire side surface, 20 first circumferential main groove, 21 second circumferential main groove, 40 center land portion, 44 intermediate land portion, 45 wall surface, 46 circumferential secondary groove, 47 chamfer, 48, 49 wall surface, 50 shoulder land portion, 60 lug groove, 80, 81 sipe, 82 first straight portion, 83 second straight portion, 84 first straight portion, 85 second straight portion, 86-90 ground contact portion, 91 sipe.

Claims

1. The tread includes a center land portion including a center in the tire width direction, intermediate land portions provided on both sides of the center land portion in the tire width direction via first circumferential main grooves, and shoulder land portions provided on the outer sides of each of the two intermediate land portions in the tire width direction via second circumferential main grooves, The intermediate land portion has a circumferential sub-groove formed therein, the circumferential sub-groove having a width smaller than that of the first circumferential main groove and the second circumferential main groove and extending in the tire circumferential direction, In the intermediate land portion, a wall surface forming at least one of the first circumferential main groove and the second circumferential main groove has an opening end chamfered in a tapered shape, The circumferential sub-groove is formed in the center of the intermediate land portion in the tire width direction, In the shoulder land portion, a circumferential sub-groove extending in the tire circumferential direction and having a width smaller than that of the first circumferential main groove and the second circumferential main groove is not formed. Pneumatic tires.

2. a depth in the tire radial direction of the circumferential sub-groove that is smaller than a depth in the tire radial direction of the first circumferential main groove and a depth in the tire radial direction of the second circumferential main groove; The pneumatic tire according to claim 1 .

3. a depth of the chamfer in the tire radial direction is smaller than a depth of the circumferential sub-groove in the tire radial direction; The pneumatic tire according to claim 1 .

4. the center land portion, the two intermediate land portions, and the two shoulder land portions each have a rib shape that is continuous over the entire circumference in the tire circumferential direction; The pneumatic tire according to any one of claims 1 to 3.

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