JP2006281908A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire 2 excellent in both riding comfort and traveling performance. <P>SOLUTION: The tire 2 is equipped with a tread 4 made of cross-linked rubber. The tread 4 is equipped with a lot of lugs 14 alternately disposed at the right and left side in the rotational direction. The lug 14 is equipped with a horizontal part 24 extending from the vicinity of the equator to the outside in the axial direction, and an oblique part 26 obliquely extending from the end of the horizontal part 24 to a rear part in the rotation direction toward the end of the tread 4. The horizontal part 24 is equipped with a horizontal front side part 28 and a horizontal lateral side part 30 in the rotation direction side. The oblique part 26 is equipped with an oblique side part 32 in the rotation direction. The horizontal front side part 28 is equipped with a buffer part 34. The buffer part 26 is equipped with a flat surface 36 formed with edges being cut. The width of the buffer part 34 is not less than 5% and not more than 50% of the width of the lug 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire mainly mounted on an agricultural machine such as a tractor.

  Tires with lugs are used for agricultural machines such as tractors from the viewpoint of traction, soil removal, and the like. The lug extends obliquely from the vicinity of the tire equator toward the end of the tread. In the tread, the left lug and the right lug are alternately arranged in the rotation direction. There is a gap between adjacent lugs. The depth of the gap is larger than the depth of the groove of the passenger car tire. The width of the gap is larger than the width of the groove of the passenger car tire. When the tractor travels, vibrations are generated due to the lugs and gaps.

  As the tire rotates, the ground contact point between the tire and the ground moves from the equator toward the end of the tread along one lug. The ground contact point that reaches the end of the tread moves to the equator of the other lug, and further moves along the other lug from the equator to the end of the tread. During traveling, such a transition of the ground contact point is repeated. This transition is discontinuous. This transition also causes vibrations in the tractor.

  When moving between farmland, tractors travel on asphalt paved roads. Vibrations are particularly noticeable on this general road. Vibration impairs the riding comfort of the tractor. In recent years, when the performance of tractors is increasing, the demand for ride comfort is increasing.

  There has been proposed a tire in which vibration is reduced by providing a block-like protrusion between the lugs. This block has an adverse effect on soil removal. The block also increases the mass of the tire.

  There has been proposed a tire in which vibration is reduced by setting a large amount of lap between one lug and the other lug. With this method, vibration reduction is not sufficient.

  There has been proposed a tire in which vibration is reduced by having a hard outer layer and a soft inner layer of a lug. A tire with reduced vibration is excellent in ride comfort.

Japanese Patent Application Laid-Open No. 2003-267003 discloses an ATV tire having a chamfered block. In this tire, both traction performance and turning performance are achieved by chamfering.
JP 2003-267003 A

  The edge of the lug located on the rotation direction side arrives first on the road surface during traveling. The ridge of this lug receives a big impact when the road surface arrives first. In particular, this impact is greatest when the ground contact point that reaches the end of the tread of one lug moves to the equator of the other lug. A tire with a large impact is inferior in riding comfort because of increased vibration. In a tire provided with a soft inner layer to reduce vibration, the inner layer is exposed when the outer layer is worn away during running. A tire having an exposed inner layer is inferior in running performance because traction performance is reduced. Moreover, the manufacturing process of the tire in which a plurality of rubber layers are provided on the lug is complicated. Tires excellent in ride comfort and running performance have not been obtained yet.

  An object of the present invention is to provide a tire excellent in both ride comfort and running performance.

  The tire according to the present invention includes a tread made of a crosslinked rubber. The tread includes a number of lugs extending from the vicinity of the equator to the vicinity of the tread end. These lugs are alternately arranged on the left and right in the rotation direction. The lug includes a horizontal portion extending axially outward from the vicinity of the equator, and an oblique portion extending obliquely rearward in the rotational direction from the end of the horizontal portion toward the end of the tread. The horizontal portion includes a horizontal front side portion and a horizontal side portion on the rotational direction side. This horizontal front side portion includes a buffer portion formed by chamfering or rounding. The ratio of the width of the buffer portion to the width of the lug is 5% or more and 50% or less.

  Preferably, in the tire, the oblique portion includes an oblique side portion on the rotational direction side. The horizontal side portion and the oblique side portion are provided with a buffer portion formed by chamfering or rounding.

  Preferably, in the tire, the buffer portion includes a flat surface formed by cutting off a ridge. The angle formed between the upper surface of the lug and this plane is 3 ° or more and 10 ° or less.

  Preferably, in the tire, the buffer portion includes a curved surface formed by rounding a ridge. The curvature radius of this curved surface is 3 mm or more and 10 mm or less.

  Preferably, in the tire, the oblique side portion includes a chamfer start point and an outer end. The ratio of the axial distance from the equator to the chamfer start point to the axial distance from the equator to the outer end is 40% or more and 80% or less. The oblique side from the chamfering start point to the outer end includes a buffer portion formed by chamfering or rounding.

  Preferably, in the tire, the buffer portion includes a flat surface formed by cutting off a ridge. The angle formed between the upper surface of the lug and this plane is 3 ° or more and 10 ° or less.

  Preferably, in the tire, the buffer portion includes a curved surface formed by rounding a ridge. The curvature radius of this curved surface is 3 mm or more and 10 mm or less.

  The tire according to the present invention includes a tread made of a crosslinked rubber. The tread includes a number of lugs extending from the vicinity of the equator to the vicinity of the tread end. These lugs are alternately arranged on the left and right in the rotation direction. The lug includes a center portion that extends obliquely rearward in the rotational direction from the vicinity of the equator, and a shoulder portion that extends further obliquely from the end of the center portion to the vicinity of the tread end. The lug has a shape in which the inclination angle of the shoulder portion with respect to the equator is larger than the inclination angle of the center portion. The center portion includes a center front side portion on the rotation direction side. The center front side portion includes a buffer portion formed by chamfering or rounding. The ratio of the width of the buffer portion to the height of the lug is 5% or more and 50% or less.

  Preferably, in this tire, the shoulder portion includes a shoulder side portion on the rotational direction side. The shoulder side portion includes a buffer portion formed by chamfering or rounding.

  Preferably, in the tire, the buffer portion includes a flat surface formed by cutting off a ridge. The angle formed between the upper surface of the lug and this plane is 3 ° or more and 10 ° or less.

  Preferably, in the tire, the buffer portion includes a curved surface formed by rounding a ridge. The curvature radius of this curved surface is 3 mm or more and 10 mm or less.

  In this pneumatic tire, since the edge of the lug that arrives first on the road surface is chamfered, the impact at the time of ground contact is reduced. Tires with reduced impact at the time of touching are excellent in ride comfort because vibration during running is reduced. Since the lug material, ground contact area and ground contact surface shape do not change, the running performance is maintained. Since it is not necessary to newly add a block, a soft rubber layer, etc., a tire can be produced without changing the manufacturing process.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a development view showing a part of a pneumatic tire 2 according to an embodiment of the present invention. The tire 2 is attached to an agricultural machine (typically a tractor). In FIG. 1, the left-right direction is the axial direction of the tire 2. What is indicated by an arrow A is the rotation direction of the tire 2. A one-dot chain line CL in FIG. 1 represents the equator of the tire 2.

  FIG. 2 is an enlarged cross-sectional view along the line II-II of the tire 2 of FIG. In FIG. 2, the vertical direction is the radial direction of the tire 2, and the horizontal direction is the axial direction of the tire 2. The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, and a belt 12. Although not shown, the tire 2 includes a tube. This tube is filled with air.

  The tread 4 is made of a crosslinked rubber and has a shape protruding outward in the radial direction. The tread 4 includes a large number of lugs 14. The lug 14 protrudes outward in the radial direction.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is made of a crosslinked rubber. The sidewall 6 absorbs an impact from the road surface by bending. Furthermore, the sidewall 6 prevents the carcass 10 from being damaged.

  The bead 8 extends from the sidewall 6 substantially inward in the radial direction. The bead 8 includes a core 16 and an apex 18 that extends radially outward from the core 16. The core 16 has a ring shape and includes a plurality of non-stretchable wires (typically steel wires). The apex 18 has a tapered shape that tapers outward in the radial direction, and is made of a highly hard crosslinked rubber.

  The carcass 10 includes a first ply 20 and a second ply 22. The first ply 20 and the second ply 22 are bridged between the beads 8 on both sides, and extend along the inside of the tread 4 and the sidewall 6. The first ply 20 and the second ply 22 are wound around the core 16 from the inner side to the outer side in the axial direction.

  Although not shown, the first ply 20 and the second ply 22 are made of a carcass cord and a topping rubber. The first ply 20 and the second ply 22 are inclined with respect to the equator. The absolute value of the tilt angle is usually 10 ° or more and 50 ° or less. The angle of the carcass cord of the first ply 20 with respect to the equator is opposite to the angle of the carcass cord of the second ply 22 with respect to the equator. The carcass cord is usually made of an organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 12 is located on the radially outer side of the carcass 10. The belt 12 is laminated with the carcass 10. The belt 12 reinforces the carcass 10. Although not shown, the belt 12 includes a belt cord and a topping rubber. A preferred material for the belt cord is organic fiber.

  In FIG. 1, these lugs 14 are arranged on the left and right sides of the tire 2. The left lug 14 and the right lug 14 are alternately arranged in the rotation direction. As the tire 2 rotates, the ground contact point between the tire 2 and the ground moves from the equator toward the end of the left tread 4 along the left lug 14. The ground contact point reaching the end of the tread 4 moves to the equator of the right lug 14, and moves along the right lug 14 from the equator to the end of the right tread 4. The ground contact point reaching the end of the tread 4 further moves to the equator of the left lug 14. During rotation, the transition of the ground contact point from the left lug 14 to the right lug 14 and the transition of the ground contact point from the right lug 14 to the left lug 14 are repeated. The transition of the ground contact point from the left lug 14 to the right lug 14 and the transition of the ground contact point from the right lug 14 to the left lug 14 are discontinuous.

  The lug 14 includes a horizontal portion 24 that extends axially outward from the vicinity of the equator, and an oblique portion 26 that obliquely extends rearward in the rotational direction from the end of the horizontal portion 24 toward the end of the tread 4. The horizontal portion 24 includes a horizontal front side portion 28 and a horizontal side portion 30 on the rotational direction side. The oblique portion 26 includes an oblique side portion 32 on the rotational direction side. The horizontal front side portion 28 of the tire 2 includes a buffer portion 34 formed by chamfering.

  FIG. 3 is an enlarged cross-sectional view taken along the line III-III of the tire 2 of FIG. In FIG. 3, the vertical direction is the radial direction of the tire 2. An arrow A represents the rotation direction of the tire 2. The buffer portion 34 includes a flat surface 36 formed by cutting off a ridge. In the tire 2 provided with the buffer portion 34, the impact at the time of ground contact is reduced. Since the impact at the time of grounding is mitigated, vibration during traveling is reduced. Therefore, the tire 2 is excellent in ride comfort.

  In FIG. 3, a double arrow line Wa represents the width of the lug 14. A double arrow line Wb represents the width of the buffer portion 34. The angle α represents an angle formed between the upper surface 38 of the lug 14 and the flat surface 36 provided in the buffer portion 34. This angle α is called a chamfer angle. The ratio (Wb / Wa) of the width Wb of the buffer portion 34 to the width Wa of the lug 14 is not less than 5% and not more than 50%. By setting the ratio (Wb / Wa) to 5% or more, the mass of the tire 2 is reduced and the impact mitigating effect by the buffer portion 34 is increased. The tire 2 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. In this respect, the ratio (Wb / Wa) is more preferably equal to or greater than 7% and particularly preferably equal to or greater than 10%. By setting this ratio (Wb / Wa) to 50% or less, the gripping force is maintained, so that the traction performance does not deteriorate. In this respect, the ratio (Wb / Wa) is more preferably equal to or less than 45%, and particularly preferably equal to or less than 40%.

  The chamfering angle α is 3 ° or more and 10 ° or less. By setting the chamfer angle α to 3 ° or more, the mass of the tire 2 is reduced and the impact mitigating effect by the buffer portion 34 is increased. The tire 2 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. In this respect, the chamfer angle α is more preferably 4 ° or more, and particularly preferably 5 ° or more. By setting the chamfer angle α to 10 ° or less, the gripping force is maintained, so that the traction performance does not deteriorate. In this respect, the chamfer angle α is more preferably 9 ° or less, and particularly preferably 8 ° or less.

  The size and angle of the tire 2 are measured in a state in which the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  FIG. 4 is a development view showing a part of a tire 40 according to another embodiment of the present invention. In FIG. 4, the left-right direction is the axial direction of the tire 40. An alternate long and short dash line CL in FIG. 4 represents the equator of the tire 40. A tread 42 made of a crosslinked rubber provided in the tire 40 includes a number of lugs 44 that are alternately arranged on the left and right sides in the rotation direction. In the tire 40, a horizontal front side portion 46 provided in the lug 44 includes a buffer portion 48 formed by rounding. Although not shown, the configuration of the tire 40 other than the buffer portion 48 is the same as that of the tire 2 of FIGS. 1 and 2.

  FIG. 5 is an enlarged cross-sectional view taken along line VV of the tire 40 of FIG. In FIG. 5, the vertical direction is the radial direction of the tire 40. Note that the direction of rotation of the tire 40 is indicated by an arrow A. The buffer portion 48 includes a curved surface 50 formed by rounding a ridge. A double arrow line Wc represents the width of the lug 44. A double arrow line Wd represents the width of the buffer portion 48. An arrow line R1 represents the radius of curvature of the curved surface 50. The ratio (Wd / Wc) of the width Wd of the buffer portion 48 to the width Wc of the lug 44 is not less than 5% and not more than 50%, as in the tire 40 shown in FIG.

  The curvature radius R1 is 3 mm or more and 10 mm or less. By setting the curvature radius R1 to 3 mm or more, the mass of the tire 40 is reduced and the impact mitigating effect by the buffer portion 48 is increased. The tire 40 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. In this respect, the curvature radius R1 is more preferably 4 mm or more, and particularly preferably 5 mm or more. By setting the curvature radius R1 to 10 mm or less, the gripping force is maintained, so that the traction performance does not deteriorate. In this respect, the radius of curvature R1 is more preferably 9 mm or less, and particularly preferably 8 mm or less.

  FIG. 6 is a development view showing a part of a tire 52 according to still another embodiment of the present invention. In FIG. 6, the left-right direction is the axial direction of the tire 52. A one-dot chain line CL in FIG. 6 represents the equator of the tire 52. The tread 54 made of a crosslinked rubber provided in the tire 52 also includes a number of lugs 56 that are alternately arranged on the left and right sides in the rotation direction. The tire 52 includes a buffer portion 66 formed by rounding the horizontal front side portion 58, the horizontal side portion 60, and the oblique side portion 64. Although not shown, the configuration of the tire 52 other than the buffer portion 66 is the same as that of the tire 2 of FIGS. 1 and 2.

  FIG. 7 is an enlarged cross-sectional view of the tire 52 of FIG. 6 along the line VII-VII. The buffer portion 66 includes a curved surface 68 formed by rounding a ridge. In addition, this buffer part 66 may be provided with a flat surface formed by cutting off a ridge. In FIG. 7, the double arrow line We is the width of the lug 56. A double arrow line Wf represents the width of the buffer portion 66. An arrow line R2 represents the radius of curvature of the curved surface 68. The ratio of the width Wf of the buffer 66 to the width We of the lug 56 is 5% or more and 50% or less. This curvature radius R2 is not less than 3 mm and not more than 10 mm. In such a tire 52, since the impact mitigating effect is large, vibration is reduced. Therefore, the tire 52 is excellent in ride comfort.

  FIG. 8 is a development view showing a part of a tire 70 according to still another embodiment of the present invention. The tread 72 made of crosslinked rubber provided in the tire 70 also includes a number of lugs 74 that are alternately arranged on the left and right sides in the rotation direction. In FIG. 8, the left-right direction is the axial direction of the tire 70. A one-dot chain line CL in FIG. 8 represents the equator of the tire 70. Note that the direction of rotation of the tire 70 is indicated by an arrow A.

  In FIG. 8, a point P1 of the oblique side part 80 is a chamfer start point. The point P2 is the outer end of the oblique side part 80. A double arrow line WL is an axial distance from the equator to this point P1. A double arrow line WT is an axial distance from the equator to this point P2, and corresponds to half the maximum width of the tire 70. The tire 70 includes a first buffer portion 78 on the horizontal front side portion 76, and a second buffer portion 82 on an oblique side portion 80 from the chamfering start point P1 to the outer end P2. The buffer portions of the first buffer portion 78 and the second buffer portion 82 are formed by chamfering. Since this tire is provided with the first buffer portion 78 and the second buffer portion 82, the tire 70 is also excellent in ride comfort. Although not shown, the configuration other than the first buffer portion 78 and the second buffer portion 82 provided in the lug 74 of the tire 70 is the same as that of the tire 2 of FIGS. 1 and 2.

  The ratio of the axial distance WL from the equator to this point P1 with respect to the length WT which is half the maximum width of the tire 70 is 40% or more and 80% or less. By setting this ratio (WL / WT) to 40% or more, the gripping force is maintained, so that the traction performance does not deteriorate. In this respect, the ratio (WL / WT) is more preferably equal to or greater than 45%, and particularly preferably equal to or greater than 50%. By setting the ratio (WL / WT) to 80% or less, the mass of the tire 70 is reduced and the impact mitigating effect by the second buffer portion 82 is increased. The tire 70 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. In this respect, the ratio (WL / WT) is more preferably equal to or less than 75%, and particularly preferably equal to or less than 70%.

  FIG. 9 is an enlarged cross-sectional view along the line IX-IX of the tire 70 of FIG. In FIG. 9, the second buffer portion 82 is shown. The second buffer portion 82 includes a flat surface 84 formed by cutting off a ridge. In addition, this 2nd buffer part 82 may be provided with the curved surface 68 formed by a rounded edge. A double arrow line Wg represents the width of the lug 74. A double arrow line Wh represents the width of the second buffer portion 82. The angle β represents an angle formed between the upper surface 86 of the lug 74 and the flat surface 84 provided in the second buffer portion 82. This angle β is called a chamfer angle. The ratio of the width Wh of the second buffer portion 82 to the width Wg of the lug 74 is 5% or more and 50% or less. The chamfer angle β is 3 ° or more and 10 ° or less. Since such a tire 70 has a large impact mitigating effect, vibration is reduced. Therefore, the tire 70 is excellent in ride comfort. Although not shown, the first buffer portion 78 is configured with the same width and chamfering angle as the second buffer portion 82.

  FIG. 10 is a development view showing a part of a tire 88 according to still another embodiment of the present invention. In FIG. 10, the left-right direction is the axial direction of the tire 88. A one-dot chain line CL in FIG. 10 represents the equator of the tire 88. A tread 90 made of a crosslinked rubber provided in the tire 88 includes a large number of lugs 92 extending from the vicinity of the equator to the vicinity of the end of the tread 90. These lugs 92 are alternately arranged on the left and right in the rotation direction. Although not shown, the configuration of the tire 88 other than the lug 92 is the same as that of the tire 2 of FIGS. 1 and 2. Note that the direction of rotation of the tire 88 is indicated by an arrow A.

  The lug 92 includes a center portion 94 that extends obliquely rearward in the rotational direction from the vicinity of the equator, and a shoulder portion 96 that extends further obliquely from the end of the center portion 94 to the vicinity of the end of the tread 90. The lug 92 has a shape in which the inclination angle of the shoulder portion 96 with respect to the equator is larger than the inclination angle of the center portion 94. The center portion 94 includes a center front side portion 98 on the rotational direction side. The shoulder portion 96 includes a shoulder side portion 100 on the rotational direction side. In the tire 88, the center front side portion 98 includes a buffer portion 102 formed by chamfering.

  FIG. 11 is an enlarged cross-sectional view of the tire 88 of FIG. 10 along the line XI-XI. In FIG. 11, the vertical direction is the radial direction of the tire 88. Note that the direction of rotation of the tire 88 is indicated by an arrow A. The buffer portion 102 includes a flat surface 104 formed by cutting off a ridge. A double arrow line Wd represents the height of the lug 92. A double arrow line Wc represents the width of the buffer portion 102. The angle γ represents an angle formed between the upper surface 106 of the lug 92 and the plane 104 provided in the buffer portion 102. This angle γ is referred to as a chamfer angle. The ratio (Wk / Wj) of the width Wk of the buffer portion 102 to the height Wj of the lug 92 is not less than 5% and not more than 50%. By setting the ratio (Wk / Wj) to 5% or more, the mass of the tire 88 is reduced and the impact mitigating effect by the buffer portion 102 is increased. The tire 88 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. In this respect, the ratio (Wk / Wj) is more preferably equal to or greater than 7% and particularly preferably equal to or greater than 10%. By setting this ratio (Wk / Wj) to 50% or less, the gripping force is maintained, so that the traction performance does not deteriorate. In this respect, the ratio (Wk / Wj) is more preferably equal to or less than 45%, and particularly preferably equal to or less than 40%.

  The chamfering angle γ is 3 ° or more and 10 ° or less. By setting the chamfering angle γ to 3 ° or more, the mass of the tire 88 is reduced and the impact mitigating effect by the buffer portion 102 is increased. The tire 88 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. From this viewpoint, the chamfer angle γ is more preferably 4 ° or more, and particularly preferably 5 ° or more. By setting the chamfering angle γ to 10 ° or less, the gripping force is maintained, so that the traction performance does not deteriorate. From this viewpoint, the chamfer angle γ is more preferably 9 ° or less, and particularly preferably 8 ° or less.

  FIG. 12 is a development view showing a part of a tire 108 according to still another embodiment of the present invention. In FIG. 12, the left-right direction is the axial direction of the tire 108. A one-dot chain line CL in FIG. 12 represents the equator of the tire 108. The tread 110 made of a crosslinked rubber provided in the tire 108 also includes a number of lugs 112 that are alternately arranged on the left and right sides in the rotation direction. Also in the tire 108, the center front side portion 114 includes a buffer portion 116 formed by rounding. Although not shown, the configuration of the tire 108 other than the buffer portion 116 of the lug 112 is the same as that of the tire 88 of FIGS. 10 and 11.

  FIG. 13 is an enlarged cross-sectional view of the tire 108 of FIG. 12 taken along line XIII-XIII. In FIG. 13, the vertical direction is the radial direction of the tire 108. Note that the direction of rotation of the tire 108 is indicated by an arrow A. The buffer portion 116 includes a curved surface 118 formed by rounding the ridge. A double arrow line Wm represents the height of the lug 112. A double arrow line Wn represents the width of the buffer portion 116. The arrow line R3 represents the radius of curvature of the curved surface 118. Also in the tire 108, the ratio (Wn / Wm) of the width Wn of the buffer portion 116 to the height Wm of the lug 112 is 5% or more and 50% or less.

  The curvature radius R3 is 3 mm or more and 10 mm or less. By setting the curvature radius R3 to 3 mm or more, the mass of the tire 108 is reduced and the impact mitigating effect by the buffer portion 116 is increased. The tire 108 having a large impact relaxation effect is excellent in ride comfort because vibration is reduced. In this respect, the curvature radius R3 is more preferably 4 mm or more, and particularly preferably 5 mm or more. By setting the curvature radius R3 to 10 mm or less, the grip force is maintained, so that the traction performance does not deteriorate. In this respect, the curvature radius R3 is more preferably 9 mm or less, and particularly preferably 8 mm or less.

  FIG. 14 is a development view showing a part of a tire 120 according to still another embodiment of the present invention. In FIG. 14, the left-right direction is the axial direction of the tire 120. An alternate long and short dash line CL in FIG. 14 represents the equator of the tire 120. The tread 122 made of a crosslinked rubber provided in the tire 120 is also provided with a number of lugs 124 that are alternately arranged on the left and right in the rotation direction. The tire 120 includes a first buffer portion 128 at the center front side portion 126 and a second buffer portion 132 at the shoulder side portion 130. The first buffer portion 128 and the second buffer portion 132 are formed by chamfering. Although not shown, the configuration of the tire 120 other than the first buffer portion 128 and the second buffer portion 132 is the same as that of the tire 88 of FIGS. 10 and 11.

  FIG. 15 is an enlarged cross-sectional view of the tire 120 of FIG. 14 along the XV-XV line. In FIG. 15, the vertical direction is the radial direction of the tire 120. Note that the direction of rotation of the tire 120 is indicated by an arrow A. In FIG. 15, the first buffer portion 128 is shown. The first buffer portion 128 includes a flat surface 134 formed by cutting a ridge. A double arrow line Wo represents the height of the lug 124 on the equator of the tire 120. A double arrow line Wp represents the width of the first buffer portion 128. The angle δ represents an angle formed between the upper surface 136 of the lug 124 and the flat surface 134 provided in the second buffer portion 132. This angle δ is referred to as a chamfer angle. In the tire 120, the ratio (Wp / Wo) of the width Wp of the first buffer portion 128 to the height Wo of the lug 124 is 5% or more and 50% or less. The chamfering angle δ is 3 ° or more and 10 ° or less. Since such a tire 120 has a large impact mitigating effect, vibration is reduced. Therefore, the tire 120 is excellent in ride comfort. Although not shown, the second buffer portion 132 is configured with the same width and chamfering angle as the first buffer portion 128.

  FIG. 16 is a development view showing a part of a tire 138 according to still another embodiment of the present invention. In FIG. 16, the left-right direction is the axial direction of the tire 138. An alternate long and short dash line CL in FIG. 16 represents the equator of the tire 138. The tread 140 made of a crosslinked rubber provided in the tire 138 also includes a number of lugs 142 that are alternately arranged on the left and right sides in the rotation direction. The tire 138 includes a first buffer portion 146 at the center front side portion 144 and a second buffer portion 150 at the shoulder side side portion 148. The first buffer portion 146 and the second buffer portion 150 are formed by chamfering. Although not shown, the configuration of the tire 138 other than the first buffer portion 148 and the second buffer portion 150 is the same as that of the tire 88 of FIGS. 10 and 11.

  17 is an enlarged cross-sectional view of the tire 138 in FIG. 16 along the line XVII-XVII. In FIG. 17, the vertical direction is the radial direction of the tire 138. Note that the direction of rotation of the tire 138 is indicated by an arrow A. FIG. 17 shows the first buffer portion 148. The first buffer portion 148 includes a curved surface 152 formed by rounding a ridge. A double arrow line Wq represents the height of the lug 142 on the equator of the tire 138. A double arrow line Wr represents the width of the first buffer portion 148. An arrow line R4 represents the radius of curvature of the curved surface 152. Also in the tire 138, the ratio (Wr / Wq) of the width Wr of the first buffer portion 148 to the height Wq of the lug 142 is 5% or more and 50% or less. The curvature radius R4 is 3 mm or more and 10 mm or less. Since such a tire 138 has a large impact mitigating effect, vibration is reduced. Therefore, the tire 138 is excellent in ride comfort. Although not shown, the second buffer part 150 has the same width and curvature radius as the first buffer part 148.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Experiment 1 Tire with a horizontal part and an oblique part on the lug]
[Example 1]
A tire of Example 1 having the basic configuration shown in FIGS. 1, 2 and 3 and having the specifications shown in Table 1 below was obtained. The tire size is 13.6-24. A first ply and a second ply were used for the carcass. The cord material used for the first ply and the second ply is nylon fiber. The angle formed with respect to the rotation direction of the cord is 35 °. The ratio of the width of the buffer portion to the width of the lug is 30%. The chamfer angle is 5 °.

[Comparative Examples 2 and 3 and Examples 2, 3, 4, 7 and 8]
A tire was obtained in the same manner as in Example 1 except that the ratio of the width of the buffer portion to the width of the lug was as shown in Tables 1 and 2 below.

[Examples 5 and 6]
A tire was obtained in the same manner as in Example 1 except that the chamfer angle was changed as shown in Table 1 below.

[Comparative Example 1]
A tire was obtained in the same manner as in Example 1 except that the buffer portion was not provided. This tire is a commercially available tire.

[Examples 9 to 13]
Tires of Examples 9 to 13 having the basic configuration shown in FIGS. 4 and 5 and having the specifications shown in Table 2 below were obtained. These tires have the same configuration as that of the first embodiment except for the buffer portion provided in the lug.

[Example 14]
A tire of Example 14 having the basic configuration shown in FIGS. 8 and 9 and having the specifications shown in Table 2 below was obtained. These tires have the same configuration as that of the first embodiment except for the buffer portion provided in the lug.

[Example 15]
A tire of Example 15 having the basic configuration shown in FIGS. 6 and 7 and having the specifications shown in Table 2 below was obtained. These tires have the same configuration as that of the first embodiment except for the buffer portion provided in the lug.

[Vibration evaluation]
A prototype tire was mounted on an agricultural tractor. The rim was 24 × W11 and the tire air pressure was 100 kPa. A driving test was conducted on a test course simulating fields and wetlands, and a driver's sensory evaluation on vibration was performed with 10 points being full. It is shown that the larger this value, the greater the vibration reduction effect and the better the ride comfort. The results are shown in Tables 1 and 2 below.

  As shown in Tables 1 and 2, the tires of the examples have a great vibration reduction effect, so that the riding comfort is improved.

[Experiment 2: Tire with center and shoulder on lug]
[Example 19]
A tire of Example 19 having the basic configuration shown in FIGS. 10 and 11 and having the specifications shown in Table 3 below was obtained. The tire size is 13.6-24. A first ply and a second ply were used for the carcass. The cord material used for the first ply and the second ply is nylon fiber. The angle formed with respect to the rotation direction of the cord is 35 °. The ratio of the buffer width to the lug height is 30%. The chamfer angle is 5 °.

[Comparative Examples 5 and 6 and Examples 16, 17 and 21]
A tire was obtained in the same manner as in Example 19 except that the ratio of the width of the buffer portion to the height of the lug was as shown in Table 3 below.

[Examples 18 and 20]
A tire was obtained in the same manner as in Example 19 except that the chamfer angle was changed as shown in Table 3 below.

[Comparative Example 4]
A tire was obtained in the same manner as in Example 19 except that the buffer portion was not provided. This tire is a commercially available tire.

[Examples 22 to 26]
Tires of Examples 22 to 26 having the basic configuration shown in FIGS. 12 and 13 and having the specifications shown in Table 4 below were obtained. These tires have the same configuration as that of Example 19 except for the buffer portion provided in the lug.

[Example 27]
A tire of Example 27 having the basic configuration shown in FIGS. 14 and 15 and having the specifications shown in Table 4 below was obtained. These tires have the same configuration as that of Example 19 except for the buffer portion provided in the lug.

[Example 15]
A tire of Example 28 having the basic configuration shown in FIGS. 16 and 17 and having the specifications shown in Table 4 below was obtained. These tires have the same configuration as that of Example 19 except for the buffer portion provided in the lug.

[Vibration evaluation]
A prototype tire was mounted on an agricultural tractor. The rim was 24 × W11 and the tire air pressure was 100 kPa. A driving test was conducted on a test course simulating fields and wetlands, and a driver's sensory evaluation on vibration was performed with 10 points being full. It is shown that the larger this value, the greater the vibration reduction effect and the better the ride comfort. The results are shown in Tables 3 and 4 below.

  As shown in Tables 3 and 4, the tires of the examples have a great vibration reduction effect, so that the ride comfort is improved. From the above evaluation results, the superiority of the present invention is clear.

  The pneumatic tire according to the present invention can be mounted on various agricultural machines.

FIG. 1 is a development view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view along the line II-II of the tire of FIG. FIG. 3 is an enlarged cross-sectional view along the line III-III of the tire of FIG. FIG. 4 is a development view showing a part of a tire according to another embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view along the line VV of the tire of FIG. FIG. 6 is a development view showing a part of a tire according to still another embodiment of the present invention. FIG. 7 is an enlarged cross-sectional view of the tire of FIG. 6 along the line VII-VII. FIG. 8 is a developed view showing a part of a tire according to still another embodiment of the present invention. FIG. 9 is an enlarged cross-sectional view along the line IX-IX of the tire of FIG. FIG. 10 is a development view showing a part of a tire according to still another embodiment of the present invention. 11 is an enlarged cross-sectional view of the tire of FIG. 10 along the line XI-XI. FIG. 12 is a developed view showing a part of a tire according to still another embodiment of the present invention. FIG. 13 is an enlarged cross-sectional view of the tire of FIG. 12 taken along line XIII-XIII. FIG. 14 is a development view showing a part of a tire according to still another embodiment of the present invention. FIG. 15 is an enlarged cross-sectional view along the line XV-XV of the tire of FIG. FIG. 16 is a development view showing a part of a tire according to still another embodiment of the present invention. 17 is an enlarged cross-sectional view of the tire of FIG. 16 taken along line XVII-XVII.

Explanation of symbols

2, 40, 52, 70, 88, 108, 120, 138 ... tyre 4, 42, 54, 72, 90, 110, 122, 140 ... tread 6 ... side wall 8 ... bead 10 ... Carcass 12 ... Belt 14, 44, 56, 74, 92, 112, 124, 142 ... Lug 16 ... Core 18 ... Apex 20 ... First ply 22 ... Second ply 24 ... Horizontal part 26 ... Oblique part 28, 46, 58, 76 ... Horizontal front side part 30, 60 ... Horizontal side part 32, 64, 80 ... Oblique side Side part 34, 48, 66, 82, 102, 116, 132, 150 ... buffer part 36, 84, 104, 134 ... plane 38, 86, 106, 136 ... upper surface 50, 68, 118 152 ... curved surfaces 78, 128, 1 6 ... 1st buffer part 82, 132, 150 ... 2nd buffer part 94 ... Center part 96 ... Shoulder part 98, 114, 126, 144 ... Center front side part 100, 130, 148 ... shoulder side

Claims (11)

It has a tread made of crosslinked rubber,
This tread has a number of lugs extending from the equator vicinity to the tread edge,
These lugs are arranged alternately on the left and right in the rotation direction,
The lug includes a horizontal portion extending outward in the axial direction from the vicinity of the equator, and an oblique portion extending obliquely rearward in the rotational direction from the end of the horizontal portion toward the end of the tread.
This horizontal part is provided with a horizontal front side part and a horizontal side part on the rotational direction side,
This horizontal front side has a buffer part formed by chamfering or rounding,
A tire in which the ratio of the width of the buffer portion to the width of the lug is 5% or more and 50% or less. The oblique part includes an oblique side part on the rotational direction side,
The tire according to claim 1, wherein the horizontal side portion and the oblique side portion are provided with a buffer portion formed by chamfering or rounding. The buffer portion includes a flat surface formed by cutting off a ridge,
The tire according to claim 1 or 2, wherein an angle formed between the upper surface of the lug and the plane is 3 ° or more and 10 ° or less. The buffer portion has a curved surface formed by rounding the ridge,
The tire according to claim 1 or 2, wherein a radius of curvature of the curved surface is 3 mm or more and 10 mm or less. The oblique side portion includes a chamfer start point and an outer end,
The ratio of the axial distance from the equator to the chamfer start point to the axial distance from the equator to the outer edge is 40% or more and 80% or less,
The tire according to claim 1, wherein the oblique side portion from the chamfer start point to the outer end includes a buffer portion formed by chamfering or rounding. The buffer portion includes a flat surface formed by cutting off a ridge,
The tire according to claim 1 or 5, wherein an angle formed between the upper surface of the lug and the plane is 3 ° or more and 10 ° or less. The buffer portion has a curved surface formed by rounding the ridge,
The tire according to claim 1 or 5, wherein a radius of curvature of the curved surface is 3 mm or more and 10 mm or less. It has a tread made of crosslinked rubber,
This tread has a number of lugs extending from the equator vicinity to the tread edge,
These lugs are arranged alternately on the left and right in the rotation direction,
The lug includes a center portion extending obliquely rearward in the rotational direction from the vicinity of the equator, and a shoulder portion extending further obliquely from the end of the center portion to the vicinity of the tread end,
This lug has a shape in which the inclination angle of the shoulder portion with respect to the equator is larger than the inclination angle of the center portion,
This center part has a center front side part on the rotational direction side,
This center front side has a buffer part formed by chamfering or rounding,
A tire in which the ratio of the width of the buffer portion to the height of the lug is 5% or more and 50% or less. The shoulder portion includes a shoulder side portion on the rotational direction side thereof,
The tire according to claim 6, wherein the shoulder side portion includes a buffer portion formed by chamfering or rounding. The buffer portion includes a flat surface formed by cutting off a ridge,
The tire according to claim 6 or 7, wherein an angle formed by the upper surface of the lug and the flat surface is 3 ° or more and 10 ° or less. The buffer portion has a curved surface formed by rounding the ridge,
The tire according to claim 6 or 7, wherein the curvature radius of the curved surface is 3 mm or more and 10 mm or less.

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