Pneumatic tire

Abstract

To reduce air resistance in a pneumatic tire including a side block.SOLUTION: A pneumatic tire 1 that is an example of an embodiment includes a tread 2 and a sidewall 3. The sidewall 3 includes a side block 3b. At the inner end of the side block 3b in a tire radial direction, there is formed a protrusion 30 protruding outward in a tire axial direction. The height H2 of the protrusion 30 is, for example, 1.1 times or more and 3.0 times or less the height H1 of the highest portion of the side block 3b other than the protrusion 30.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having side blocks.

Background Art

[0002] In recent years, from the viewpoint of improving the fuel efficiency performance of vehicles, etc., reduction of air resistance has also been demanded for tires. Conventionally, in order to improve the traction performance, side cut performance, etc. during off-road driving, a pneumatic tire having side blocks formed on the sidewall has been widely known (for example, see Patent Document 1), but when there are side blocks, it becomes more difficult to reduce air resistance. Generally, side blocks increase the air resistance of the tire.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to reduce air resistance in a pneumatic tire having side blocks.

Means for Solving the Problems

[0005] A pneumatic tire according to one aspect of the present invention is a pneumatic tire including a tread and a sidewall, wherein the sidewall has side blocks, and a protrusion protruding outward in the tire axial direction is formed at the radially inner end of the side blocks in the tire diameter direction.

Effects of the Invention

[0006] According to one aspect of the present invention, in a pneumatic tire provided with side blocks, air resistance can be reduced.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0008] Hereinafter, with reference to the drawings, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail. The embodiments described below are merely examples, and the present invention is not limited to the following embodiments. In addition, a mode formed by selectively combining each component of a plurality of embodiments and modification examples described below is included in the present invention.

[0009] FIG. 1 is a perspective view of a pneumatic tire 1 according to an example of an embodiment. As shown in FIG. 1, the pneumatic tire 1 includes a tread 2 that is a portion in contact with the road surface, a sidewall 3 that forms the tire side surface, and a bead 4 that is a portion fixed to the rim of the wheel. The tread 2 has a tread pattern including a plurality of blocks such as shoulder blocks 2a and 2b. Further, a plurality of grooves 2c and 2d that partition the blocks are formed in the tread 2. The tread 2, the sidewall 3, and the bead 4 are formed in an annular shape along the tire circumferential direction.

[0010] The sidewall 3 extends radially inward from both axial ends of the tread 2 in the tire axial direction and forms the left and right side surfaces of the pneumatic tire 1 together with the bead 4. Although details will be described later, the sidewall 3 has side blocks 3b that protrude outward in the tire axial direction from the profile surface 3a of the sidewall 3. The side blocks 3b improve the traction performance and side cut performance during off-road driving. Further, a protrusion 30 for reducing air resistance is formed at the radially inner end of the side block 3b in the tire radial direction.

[0011] The pneumatic tire 1 is suitable for, for example, a tire for a light truck. Note that light trucks include pickup trucks, sports utility vehicles (SUVs), and the like. An example of the size of the pneumatic tire 1 is LT275 / 60R20.

[0012] A side rib 5 is formed in the pneumatic tire 1 in the vicinity of the tread 2 on the tire side surface. The side rib 5 is a convex portion that protrudes outward in the tire axial direction and is formed in an annular shape along the tire circumferential direction. In the present embodiment, a portion from the outer axial end of the surface of the shoulder blocks 2a and 2b facing the outer side in the tire radial direction to the side rib 5 is defined as a buttress region, and a portion from the bead 4 to the side rib 5 is defined as the sidewall 3. Note that the shape of the side surfaces 6a and 6b of the shoulder blocks 2a and 2b facing the outer side in the tire axial direction affects the shape of the buttress region.

[0013] The tread 2 and the sidewall 3 are generally made of different types of rubber. The buttress area may be made of the same rubber as the tread 2 or may be made of different rubber. The bead 4 has, for example, a bead core and a bead filler. The bead core is a ring-shaped member in which bundled steel wires (bead wires) are coated with rubber. The bead filler is made of a rubber harder than the tread rubber and the sidewall rubber and has a function of enhancing the rigidity of the bead 4.

[0014] The pneumatic tire 1 includes, for example, a carcass, a belt, and an inner liner. The carcass is a cord layer coated with rubber and forms the framework of the pneumatic tire 1 that withstands loads, impacts, air pressure, etc. The belt is a reinforcing band disposed between the rubber constituting the tread 2 and the carcass. The belt strongly tightens the carcass to enhance the rigidity of the pneumatic tire 1. The inner liner is a rubber layer provided on the inner peripheral surface of the carcass and holds the air pressure of the pneumatic tire 1.

[0015] FIG. 1 shows the side block 3b on the left side surface of the pneumatic tire 1. The pneumatic tire 1 preferably has side blocks 3b on the left and right sidewalls 3. And it is preferable that protrusions 30 are formed on both the left and right side blocks 3b. However, the left and right side blocks 3b are not limited to blocks of the same shape and may have completely different shapes. The side block 3b on the right side surface has, for example, a shape obtained by rotating the side block 3b on the left side surface 180° about a center line passing through the tire equator and perpendicular to the tire rotation axis. The pneumatic tire 1 may be a tire without a specified mounting direction.

[0016] Hereinafter, with further reference to FIG. 2, the sidewall 3 and the beadless region of the pneumatic tire 1 will be described in detail. FIG. 2 is a left side view of the pneumatic tire 1, showing an enlarged sidewall 3 and beadless region. Hereinafter, the first direction in the tire circumferential direction may be referred to as the "X1 direction", and the second direction may be referred to as the "X2 direction". Also, the direction facing the outer side in the tire radial direction may be referred to as the "Y1 direction", and the direction facing the inner side in the radial direction may be referred to as the "Y2 direction".

[0017] As shown in FIGS. 1 and 2, the pneumatic tire 1 has a plurality of side blocks 3b formed in the sidewall 3. The plurality of side blocks 3b are arranged at a predetermined interval in the tire circumferential direction. The predetermined interval may be constant, or may be a variable pitch in which the interval between the blocks and the circumferential length of the blocks are slightly changed in units of a predetermined number. Also, the side block 3b includes a first side block 10 and a second side block 20. A step is formed at the boundary 15 between the first side block 10 and the second side block 20, and the first side block 10 protrudes more than the second side block 20.

[0018] In the present embodiment, side blocks 3b having substantially the same shape and the same size are arranged in the tire circumferential direction, but two or more types of blocks having different shapes may be arranged alternately or in a predetermined pattern in the tire circumferential direction. The number of side blocks 3b arranged in the tire circumferential direction is not particularly limited, but as an example, it is 20 or more and 30 or less.

[0019] The side block 3b is preferably formed between the side rib 5 and the tire maximum width position P. In this case, it becomes easy to reduce air resistance while ensuring good side traction performance and side cut (protection) performance. In this specification, the "tire maximum width position P" means the position where the tire axial direction length is maximum on the profile surface 3a of the sidewall 3. Also, the "profile surface 3a" of the sidewall 3 means the surface facing the outside in the tire axial direction of the sidewall 3 when the side block 3b is not formed. For the virtual surface along the surface of the sidewall 3 and the surface hidden by the side block 3b, it is distinguished from the exposed surface and is referred to as the "profile surface 3x".

[0020] The side block 3b is a block in which one first side block 10 and one second side block 20 are connected and integrated. The lengths of the first side block 10 and the second side block 20 along the tire radial direction are substantially the same, and at the inner end in the tire radial direction of each block, a protrusion 30 extending in the tire circumferential direction is formed. Although it will be described in detail later, the protrusion 30 is formed substantially parallel to the side rib 5. The protrusion 30 realizes the flow of air along the surface of the sidewall 3 and effectively reduces the air resistance during running.

[0021] The portion located between the side blocks 3b is at the same height as the profile surface 3a of the sidewall 3. For this reason, irregularities are formed in the tire circumferential direction in the portion of the sidewall 3 located between the side rib 5 and the tire maximum width position P. These irregularities improve the side traction performance on muddy ground, sandy ground, or snow-covered roads. From the viewpoint of improving the side cut performance, the length of the side block 3b along the tire circumferential direction is preferably longer than the interval between the side blocks 3b.

[0022] The side blocks 3b and the shoulder blocks 2a, 2b of the tread 2 are preferably arranged in a regular pattern related to each other. In this case, a unified and regular pattern is formed in the sidewall 3 and the buttress area. For example, the side traction performance is stabilized and the air resistance reduction effect is also improved. In this embodiment, the first side block 10 is formed so as to be aligned with the shoulder block 2a in the tire radial direction, and the second side block 20 is formed so as to be aligned with the shoulder block 2b in the tire radial direction.

[0023] The shoulder blocks 2a, 2b are blocks formed in the outer portion in the tire axial direction of the tread 2 and are arranged alternately in the tire circumferential direction. The shoulder blocks 2a, 2b have, for example, similar sizes to each other, but are different in shape in that the side surface 6b of the shoulder block 2b is recessed more than the side surface 6a of the shoulder block 2a. The side surface 6b of the shoulder block 2b has a step formed over the entire length in the tire circumferential direction of the side surface 6b, and the block surface side is recessed more than the side rib 5 side.

[0024] The shoulder blocks 2a, 2b are separated by grooves 2c, 2d extending in the tire axial direction. The groove 2c is formed with substantially the same width from between the blocks to the side rib 5, while the groove 2d widens in the vicinity of the side rib 5. The side surfaces 6a, 6b of the shoulder blocks 2a, 2b and the grooves 2c, 2d form irregularities in the tire circumferential direction in the buttress area of the pneumatic tire 1. Similar to the side blocks 3b, these irregularities improve the side traction performance on muddy ground, sandy ground, or snow-covered roads.

[0025] The side block 3b is formed in a range that overlaps with the shoulder blocks 2a, 2b and the groove 2c in the tire radial direction, and is not formed in the portion that overlaps with the groove 2d in the tire radial direction. That is, the side blocks 3b are formed at the same pitch as the pair of shoulder blocks 2a, 2b in the tire circumferential direction. The interval between the side blocks 3b is wider on the tire maximum width position P side than on the side rib 5 side. In this case, for example, in muddy ground, the mud discharging property is improved and the side traction performance is enhanced.

[0026] The first side block 10 constituting the side block 3b is sandwiched between two second side blocks 20, is continuous with one of the second side blocks 20, and is not connected to the other second side block 20. The first side block 10 is formed in a range that overlaps with the shoulder block 2a in the tire radial direction, and the second side block 20 is formed in a range that overlaps with the shoulder block 2b and the groove 2c in the tire radial direction. The second side block 20 is larger than the first side block 10, and a part of it extends to a position that overlaps with the shoulder block 2a in the tire radial direction. In this embodiment, the second side block 20 overlaps with the groove 2c in the tire radial direction, but the first side block 10 may overlap with the groove 2c in the tire radial direction.

[0027] As described above, the first side block 10 and the second side block 20 have different heights from each other, and the first side block 10 is formed higher. The height H1 of the side block 3b (see FIG. 4 described later) means the length along the normal direction of the profile surface 3x from the profile surface 3x of the sidewall 3 to the surface of the side block 3b. Due to the height difference between the two blocks constituting the side block 3b and the height difference between the side block 3b and its gap, irregularities are formed on the sidewall 3, and these irregularities improve the side traction performance on muddy ground, sandy ground, or snowy roads.

[0028] The first side block 10 has substantially the same height, for example, except for the protrusion 30 at the inner end in the tire radial direction and the block end. On the other hand, the second side block 20 has three regions (the first region 21, the second region 22, and the third region 23) with different heights along the tire radial direction. The height of the second side block 20 is substantially constant in the first region 21 adjacent to the side rib 5 and is lowest at the boundary between the second region 22 and the third region 23. Regarding the protrusion 30, it is formed at the same height in the first side block 10 and the second side block 20.

[0029] The portion of the first side block 10 located on the inner side in the tire radial direction has a shape convex in the X1 direction. This convex portion 11 is formed, for example, in a length range of 30% or more and 70% or less of the tire radial length of the first side block 10 from the inner end in the tire radial direction (the end in the Y2 direction). In other words, the portion of the first side block 10 located on the outer side (the Y1 direction side) closer to the side rib 5 in the tire radial direction has a shape concave in the X2 direction. Such unevenness of the first side block 10 contributes to the improvement of the side traction performance. The X1 direction end of the convex portion 11 is formed substantially linearly in side view along the tire radial direction.

[0030] The block end of the side block 3b may be formed perpendicular to the profile surface 3a or may be inclined so that the height of the block gradually decreases. At the end of the convex portion 11 of the first side block 10, a slope 12 with a gentler inclination than other block ends is formed. The slope 12 is located at the block end facing the Y1 direction. By forming the gentle slope 12 at the Y1 direction end of the convex portion 11, an air flow along the surface of the sidewall 3 is likely to occur, and an increase in air resistance can be suppressed. The inclination angle of the slope 12 with respect to the profile surface 3x is, for example, 40° or more and 75° or less.

[0031] The boundary 15 between the two blocks that make up the side block 3b extends along the tire radial direction from the side rib 5 and bends in the X1 direction at the center of the block in the tire radial direction. For this reason, the portion located on the Y2-direction side of the first side block 10 gradually decreases in tire circumferential length in the Y2 direction. Since the first side block 10 and the second side block 20 have different heights, a step is formed along the boundary 15.

[0032] As described above, the height of the second side block 20 changes in the tire radial direction. In the portion other than the protrusion 30, the first region 21 adjacent to the side rib 5 is the highest. The second region 22 adjacent to the first region 21 in the Y2 direction slopes so that the height gradually decreases in the Y2 direction, and the third region 23 adjacent to the second region 22 in the Y2 direction slopes so that the height gradually increases in the Y2 direction. By providing a gentle slope on the surface of the second side block 20, an air flow along the surface of the second side block 20 is likely to occur, and an increase in air resistance can be suppressed.

[0033] The block end of the second side block 20 facing the X2 direction is inclined with respect to the tire radial direction so that it is gradually positioned in the X1 direction in the Y2 direction. The second side block 20 has a tapered shape with a slightly shorter tire circumferential length at the Y2-direction end than at the Y1-direction end.

[0034] Hereinafter, with reference to FIGS. 2 to 4, the protrusion 30 of the side block 3b will be described in more detail. FIG. 3 is a view showing a part of the cross section taken along line AA in FIG. 2. FIG. 4 is a cross-sectional view of the protrusion 30 and its vicinity.

[0035] As shown in FIGS. 2 to 4, on the inner end in the tire diameter direction (end in the Y2 direction) of the side block 3b, as described above, a protrusion 30 protruding outward in the tire axial direction is formed. The protrusion 30 protrudes more than other parts of the side block 3b. As a result of the study by the present inventors, it was found that the air resistance of the tire can be effectively reduced by suppressing the convection and vortices generated in the vicinity of the sidewall 3 and creating an air flow along the surface of the sidewall 3. And, by providing the protrusion 30 at the Y2-direction end of the side block 3b, a smooth air flow along the surface of the sidewall 3 has been successfully realized.

[0036] The protrusion 30 only needs to be formed at the Y2-direction end of the side block 3b, but is preferably formed within a length range corresponding to 20% of the tire cross-sectional height H (see FIG. 1) from the tire maximum width position P. In this case, the effect of providing the protrusion 30 becomes more remarkable. In particular, it is preferable to form the protrusion 30 at the tire maximum width position P or on the tread 2 side of the maximum width position P. In the present embodiment, the protrusion 30 is formed on the tread 2 side of the tire maximum width position P and in the vicinity of the tire maximum width position P. Since the tire rotates at high speed during vehicle running, the radial grooves do not significantly affect the air resistance, and as described above, creating an air flow along the surface of the sidewall 3 is considered important for reducing the air resistance.

[0037] The protrusion 30 is preferably located within a length range corresponding to 10% or 5% of the tire cross-sectional height H in the Y1 direction from the tire maximum width position P. Since the protrusion 30 is formed at the Y2-direction end of the side block 3b, the Y2-direction end of the block needs to be located within this range. The tip 33 of the protrusion 30 is located, for example, within a length range corresponding to 5% of the tire cross-sectional height H in the Y1 direction from the tire maximum width position P. The tip 33 is the portion where the height of the protrusion 30 is the highest.

[0038] The height H2 of the protrusion 30 is preferably 1.1 times or more and 3.0 times or less the height H1 of the highest part of the side block 3b other than the protrusion 30. In this case, the effect of reducing air resistance due to the provision of the protrusion 30 becomes more prominent. In the present embodiment, the highest part of the side block 3b other than the protrusion 30 is the surface of the first side block 10. The height H2 of the protrusion 30 (similarly for the height H1) means the length along the normal direction of the profile surface 3x from the profile surface 3x to the highest part (tip 33) of the protrusion 30.

[0039] The height H2 of the protrusion 30 is more preferably 1.1 times or more and 2.5 times or less the height H1, particularly preferably 1.3 times or more and 2.0 times or less, and most preferably 1.4 times or more and 1.9 times or less. An example of the height H1 of the side block 3b is 1 mm or more and 15 mm or less, or 2 mm or more and 10 mm or less, or 3 mm or more and 5 mm or less. If the height of the protrusion 30 is within the above range, the effect of reducing air resistance becomes more prominent. If the height H2 of the protrusion 30 is too low, the effect of the protrusion 30 becomes small, and if the height H2 is too high, the air resistance may instead increase. The height H2 of the protrusion 30 is, for example, 2 mm or more and 18 mm or less, or 3 mm or more and 17 mm or less, or 5 mm or more and 15 mm or less.

[0040] The protrusion 30 may be formed only on one of the first side block 10 or the second side block 20, but is preferably formed on both blocks. As described above, since the tire diameter direction lengths of the first side block 10 and the second side block 20 are constant, the protrusions 30 of each block are arranged along the tire circumferential direction. That is, the protrusion 30 is formed in a single gently curved linear shape in a side view of the pneumatic tire 1. In this case, it becomes easy to realize an air flow along the surface of the sidewall 3, and the effect of reducing air resistance is improved.

[0041] The height H2 of the protrusion 30 may be different between the first side block 10 and the second side block 20, but is preferably substantially the same. By making the height H2 of the protrusion 30 constant, a stable air resistance reduction effect can be obtained. Since the portion of the second side block 20 other than the protrusion 30 is lower in height than the first side block 10, the height difference between the protrusion 30 and the other portion is larger in the second side block 20 than in the first side block 10. In addition, since a gentle slope is formed along the tire diameter direction on the surface of the second side block 20, an air flow along the block surface is likely to occur.

[0042] The protrusion 30 is preferably formed on all side blocks 3b (the first side block 10 and the second side block 20). Further, a plurality of protrusions 30 are preferably formed on the circumference of the same circle α along the tire circumferential direction. In other words, a plurality of protrusions 30 are intermittently formed in the tire circumferential direction, and each protrusion 30 is arranged in a row along the tire circumferential direction. In this case, the air resistance reduction effect due to the provision of the protrusion 30 becomes more prominent. In the present embodiment, the plurality of protrusions 30 are arranged in parallel with the side rib 5 and have the same length, width, and height as each other. The circle α is a perfect circle centered on the rotation axis of the pneumatic tire 1.

[0043] The total length of the protrusions 30 along the tire circumferential direction is preferably a length of 30% or more of the circumference of the circle α, more preferably 40% or more, and particularly preferably 50% or more. In this case, the air resistance reduction effect due to the provision of the protrusions 30 becomes more prominent. The protrusions 30 may be formed in an annular shape along the tire circumferential direction. In this case, since at least the Y2-direction ends of the side blocks 3b are in a continuous state in the tire circumferential direction, it is necessary to adopt a block shape such that the side traction performance does not deteriorate. The total length of the protrusions 30 along the tire circumferential direction may exceed 50% of the circumference of the circle α. For example, it may be more than 50% and 70% or less.

[0044] The protrusion 30 includes a first inclined surface 31 formed between the surface of the side block 3b and the tip 33 of the protrusion 30, and a second inclined surface 32 formed between the profile surface 3a and the tip 33 of the protrusion 30. The first inclined surface 31 is preferably gentler in inclination than the second inclined surface 32 and has a smaller inclination angle with respect to the profile surface 3x. In this case, it becomes easier to achieve both good side traction performance and low air resistance. The tip 33 of the protrusion 30 may be pointed as shown in FIG. 4, or may be slightly curved as if chamfered.

[0045] The first inclined surface 31 of the protrusion 30 may be a straight inclined surface without unevenness, or may be a gently curved inclined surface that is convex in the Y2 direction. Also, the inclination angle of the first inclined surface 31 may gradually increase toward the tip 33. In any case, it is preferable that the inclination angle of the inclined surface with respect to the profile surface 3x is smaller for the first inclined surface 31 than for the second inclined surface 32 both in terms of the maximum value and the average value. Note that at the Y2-direction end of the side block 3b, the starting end of the first inclined surface 31 is defined as the position where the height of the side block 3b begins to increase when viewed from the Y1 direction. Note that the second inclined surface 32 is a continuous inclined surface with the inclined surface at the block end, and the boundary position with the inclined surface at the block end may not be clear.

[0046] Similar to the first inclined surface 31, the second inclined surface 32 of the protrusion 30 may be a straight inclined surface without unevenness, or may be a curved inclined surface that is convex in the Y1 direction. Also, the inclination angle of the second inclined surface 32 may gradually increase toward the tip 33, and at least a part of the second inclined surface 32 may be formed substantially perpendicular to the profile surface 3x. In the present embodiment, the second inclined surface 32 is a curved surface continuous with the inclined surface at the block end. Since the inclination of the first inclined surface 31 affects air resistance, it is preferably gentle, but since the inclination of the second inclined surface 32 is considered to have little effect on air resistance, the traction performance can be improved by making it a steep inclination.

[0047] Regarding the pneumatic tire 1 having the above configuration, by means of a simulation for analyzing the air flow around the rotating tire, the height H1 of the side block 3b and the height H2 of the protrusion 30 were changed, and the air resistance was evaluated by the following method. Also, the traction performance was evaluated by a single-wheel traction test on muddy ground. The evaluation results are shown in Table 1. The evaluation results shown in Table 1 are relative values, and the larger the numerical value, the smaller the air resistance and the higher the traction performance.

[0048] [Evaluation of air resistance] For each test tire, the drag force (the force acting on the tire placed in the air flow and in the same direction as the flow) was measured, and the drag coefficient Cd was calculated from the following formula. The drag force was obtained from the pressure difference before and after the tire by simulation. Cd = D / (1 / 2ρU2S) In the formula, D is the generated drag force. ρ is the air density, which was taken as 1.18415 [kg / m 3 . U is the representative speed, which is the relative speed between the tire and the air, and was taken as 36.1 [m / s]. S is the representative area (frontal projected area) of the tire.

[0049] [Evaluation of traction performance] Based on the single-wheel traction test "ASTM F1805" used in the snow traction evaluation, the traction performance of each test tire was evaluated on muddy ground. By this test, the longitudinal force (Fx) and the vertical load (Fz) of each test tire were obtained, and the forward traction index (μ = Fx / Fz) was obtained. The traction index (μ) of each test tire indicates the friction characteristics of the tire on the road surface where the test was conducted, and is calculated as a relative value with respect to the numerical value of the reference tire. The larger the numerical value, the better the traction performance.

[0050] This test is performed by mounting each test tire and the reference tire on one test wheel of the test vehicle and running the test course. Also, the evaluation is performed based on the following standards. ASTM F1805 ASTM F377 ASTM D2487 ASTM D4318

[0051] The load and air pressure of the tire shall be the values applicable to light truck tires. Specifically, the test load shall be 567 kgf and the air pressure shall be 345 kPa.

[0052]

Table 1

[0053] As shown in Table 1, it is understood that when H2 / H1 is 1.1 or more and 3.0 or less, while ensuring high side traction performance, air resistance can be effectively reduced. When H2 / H1 is 1.0 as in No. 5 and there is no protrusion 30, the effect of reducing air resistance cannot be obtained. Also, when H2 / H1 exceeds 3.0 as in No. 1 and No. 4, the effect of reducing air resistance cannot be obtained. When H2 / H1 is 1.4 or more and 1.9 or less, or 1.6 or more and 1.8 or less, the effect of reducing air resistance is particularly remarkable.

[0054] As described above, according to the pneumatic tire 1 having the above configuration, in the tire provided with the side block 3b, air resistance can be effectively reduced. The protrusion 30 formed at the radially inner end of the side block 3b in the tire diameter direction can create an air flow along the surface of the sidewall 3, thereby greatly reducing air resistance. Also, according to the pneumatic tire 1, even if a large side block 3b is provided, an increase in air resistance can be suppressed.

[0055] According to the pneumatic tire 1, while reducing air resistance, side traction performance and side cut performance equal to or higher than those of the conventional tires can be ensured. The pneumatic tire 1 is particularly suitable for light truck tires.

[0056] Hereinafter, another example of the embodiment will be described with reference to FIGS. 5 to 8. In the following, the differences from the first embodiment will be mainly described, and the above description will be applied to the common or similar components. FIG. 5 is a perspective view showing a partially enlarged side surface of the pneumatic tire 50 according to the second embodiment, and FIG. 6 is a cross-sectional view of the side block 53b of the pneumatic tire 50 and its vicinity. FIG. 7 is a perspective view showing a partially enlarged side surface of the pneumatic tire 80 according to the third embodiment, and FIG. 8 is a cross-sectional view of the side block 53b of the pneumatic tire 80 and its vicinity.

[0057] As shown in FIGS. 5 to 8, the pneumatic tires 50 and 80 include sidewalls 53 and 83 in which side blocks 53b and 83b are formed, and are common to the pneumatic tire 1 in that protrusions 70 and 90 protruding outward in the tire axial direction are respectively formed at the radially inner ends (ends in the Y2 direction) of the side blocks 53b and 83b. Further, the pneumatic tires 50 and 80 are common to the pneumatic tire 1 in that they include treads 52 and 82 including a plurality of blocks such as shoulder blocks.

[0058] The tread 52 of the pneumatic tire 50 has shoulder blocks 52a and 52b alternately arranged in the tire circumferential direction, and grooves 52c partitioning the two blocks. Depressions 57a and 57b are respectively formed on the side surfaces 56a and 56b of the shoulder blocks 52a and 52b. The depression 57b of the shoulder block 52b is formed larger and deeper than the depression 57a of the shoulder block 52a over a wide range of the side surface 56b over the entire radial length of the side surface 56b. The depression 57a is formed long in the tire circumferential direction on the Y2 direction side of the side surface 56b.

[0059] The tread 82 of the pneumatic tire 80 has shoulder blocks 82a and 82b alternately arranged in the tire circumferential direction, and grooves 82c partitioning the two blocks. Depressions 87a and 87b are respectively formed on side surfaces 86a and 86b of the shoulder blocks 82a and 82b. The depression 87a has a shape partitioned into two in the tire radial direction, and two such depressions 87a are formed side by side in the tire circumferential direction on the side surface 86a of the shoulder block 82a. On the side surface 86b of the shoulder block 82b, two elongated depressions 87b extending in the tire radial direction are formed side by side in the tire circumferential direction. In both of the depressions 87a and 87b, the depression on the X1 direction side is formed larger than the depression on the X2 direction side.

[0060] In the buttress regions of the pneumatic tires 50 and 80, unevenness is formed in the tire circumferential direction by the depressions of each shoulder block and the grooves 52c and 82c, similar to the case of the pneumatic tire 1. This unevenness, together with the side blocks 53b and 83b, improves the side traction performance on muddy ground, sandy ground, or snowy roads.

[0061] The protrusions 70 and 90 of the pneumatic tires 50 and 80 are formed on the tread 52 and 82 sides rather than the maximum width position P of each tire. The height of the protrusions 70 and 90 is 1.1 times or more and 3.0 times or less the height of the highest part of the side blocks 53b and 83b other than the protrusions, and the preferable height range is the same as that of the protrusion 30 in the first embodiment. Also, regarding the positions of the protrusions 70 and 90 with respect to the maximum width position P of each tire, it is the same as in the case of the protrusion 30. For example, the tips 73 and 93 of the protrusions 70 and 90 are located within a length range corresponding to 5% of the tire section height H in the Y1 direction from the tire maximum width position P.

[0062] The projections 70 are formed in a plurality on the circumference of the same circle α1 along the tire circumferential direction, and it is preferable that the total length of the projections 70 along the tire circumferential direction is 50% or more of the circumferential length of the circle α1. Similarly for the projections 90, they are formed in a plurality on the circumference of the same circle α2 along the tire circumferential direction, and it is preferable that the total length of the projections 90 along the tire circumferential direction is 50% or more of the circumferential length of the circle α2. As will be described in detail later, compared with the projections 30 of the first embodiment, the projections 70 and 90 have a longer length along the tire circumferential direction.

[0063] The projection 70 includes a first inclined surface 71 formed between the surface of the side block 53b and the tip 73, and a second inclined surface 72 formed between the profile surface 53a of the sidewall 53 and the tip 73. The first inclined surface 71 is less inclined than the second inclined surface 72, and the average value and the maximum value of the inclination angle with respect to the profile surface 53x are small. Similarly for the projection 90, the first inclined surface 91 is less inclined than the second inclined surface 92. In this case, an air flow along the surfaces of the side blocks 53b and 83b is likely to occur, and the effect of reducing air resistance becomes more remarkable.

[0064] As shown in FIG. 5, the side block 53b of the pneumatic tire 50 is a block continuous in the tire circumferential direction and has a plurality of depressions 61, 62, 63. Further, at the Y2-direction end of the side block 53b, depressions 60 are formed at a predetermined interval in the tire circumferential direction. The predetermined interval may be constant or a variable pitch in which the interval between the blocks is slightly changed in units of a predetermined number. In the present embodiment, a pattern in which one each of the depressions 61, 62, 63 and the shoulder blocks 52a, 52b are arranged between two depressions 60 is repeated in the tire circumferential direction.

[0065] On the side block 53b, recesses 62 and 63 are alternately formed in the tire circumferential direction on the Y1 direction side. The recess 61 is formed on the Y2 direction side of the side block 53b so as to overlap the recesses 62 and 63 in the tire radial direction. The recesses 61, 62, and 63 are all long in the tire circumferential direction. For example, the bottom of the recess is formed to a depth such that the height is above the profile surface 53a. The recess 60 has a side view shape that notches the Y2 direction end of the side block 53b and is alternately arranged with the recess 61 in the tire circumferential direction. The Y2 direction end of the side block 53b has a shape that enters into the Y1 direction due to the recess 60. Note that in the recess 60, a substantially V-shaped ridge 64 that protrudes slightly outward in the tire axial direction from the profile surface 53a is formed in a side view.

[0066] The protrusion 70 formed at the Y2 direction end of the side block 53b is divided in the tire circumferential direction by the recess 60. The protrusion 70 is formed over the entire length of the portion other than the recess 60 on the circumference of the circle α1. The length of the protrusion 70 along the tire circumferential direction is longer than the length of the recess 60 along the tire circumferential direction. For this reason, the total length of the protrusion 70 along the tire circumferential direction exceeds 50% of the circumference length of the circle α1, and is, for example, 55% or more and 75% or less of the circumference length of the circle α1.

[0067] As shown in FIG. 7, the side blocks 83b of the pneumatic tire 80 are common to the side blocks 3b of the first embodiment in that they are arranged at predetermined intervals in the tire circumferential direction. The predetermined interval may be constant or may be a variable pitch in which the interval between the blocks is slightly changed in units of a predetermined number. On the other hand, the shape of the side blocks 83b is significantly different from that of the side blocks 3b, and the interval between the side blocks 83b is also smaller than that in the case of the side blocks 3b.

[0068] The side block 83b is formed with a plurality of depressions 88 that are rectangular in side view and extend in the tire radial direction. The depressions 88 gradually become smaller from the X1 direction to the X2 direction of the side block 83b. For example, the depression 88 located most in the X1 direction has a size that is 2 times or more and 10 times or less that of the depression 88 located most in the X2 direction. In this embodiment, six depressions 88 with different sizes are arranged side by side in the tire circumferential direction. The interval between the side blocks 83b may be the same as or smaller than the tire circumferential length of the largest depression 88.

[0069] At the Y2-direction end of the side block 83b, a protrusion 90 is formed over its entire length. The length of the protrusion 90 along the tire circumferential direction is longer than the interval between the side blocks 83b, and the total length of the protrusion 90 along the tire circumferential direction exceeds 50% of the circumferential length of the circle α2. The total length of the protrusion 90 along the tire circumferential direction is, for example, 75% or more and 95% or less of the circumferential length of the circle α2.

[0070] Also in the pneumatic tires 50, 80, due to the functions of the protrusions 70, 90, an air flow along the surface of the sidewalls 53, 83 can be created, and the air resistance can be effectively reduced.

Description of Reference Numerals

[0071] 1 Pneumatic tire, 2 Tread, 2a, 2b Shoulder block, 2c, 2d Groove, 3 Sidewall, 3a, 3x Profile surface, 3b Side block, 4 Bead, 5 Side rib, 6a, 6b Side surface, 10 First side block, 11 Convex portion, 12 Inclined surface, 15 Boundary, 20 Second side block, 21 First region, 22 Second region, 23 Third region, 30 Protrusion, 31 First inclined surface, 32 Second inclined surface, 33 Tip, P Tire maximum width position

Claims

1. A pneumatic tire comprising a tread and a sidewall, wherein the sidewall has side blocks, and projections protruding outward in the tire axial direction are formed at the inner ends of the side blocks in the tire radial direction. The pneumatic tire.

2. The height of the projection is 1.1 times or more and 3.0 times or less the height of the portion where the height of the side block is the highest other than the projection. The pneumatic tire according to claim 1.

3. A plurality of the projections are formed on the circumference of the same circle α along the tire circumferential direction, and the total length of the projections along the tire circumferential direction is 30% or more of the circumference length of the circle α. The pneumatic tire according to claim 1.

4. The projection is formed within a length range corresponding to 20% of the tire cross-sectional height from the tire maximum width position. The pneumatic tire according to claim 1.

5. The projection is formed on the tread side rather than the tire maximum width position. The pneumatic tire according to claim 4.

6. The projection includes a first inclined surface formed between the surface of the side block and the tip of the projection, and a second inclined surface formed between the profile surface of the sidewall and the tip of the projection, and the inclination angle of the first inclined surface with respect to the profile surface is smaller than that of the second inclined surface. The pneumatic tire according to claim 1.

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