Lug tires

Abstract

To provide a lugged tire 2 that suppresses the temperature rise of the lugs 16, suppresses the adhesion of mud, and allows mud to be easily removed even if it does adhere. [Solution] The tire 2 is equipped with a tread 6. The tread 6 is equipped with a plurality of lugs 16. Each lug 16 is equipped with a plurality of steps 42 on its side surface 22. Each step 42 is equipped with a stepped portion 44 and a stepped plate portion 46. Of the plurality of steps 42, the edges SGs of the outermost step 42s located radially outward are located axially outward from the protruding reference line LWE, and the starting point SSu of the innermost step 42u located radially inward is located axially inward from the protruding reference line LWE. The edges SG of the step 42 are inclined with respect to the circumferential direction. The tip Gh of the edge SG located on the rotational leading side is located radially inward from the trailing end Gt of the edge SG located on the rotational trailing side.

Description

Technical Field

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[0001] The present invention relates to a lugged tire.

Background Art

[0002] The tread of a lugged tire includes a plurality of lugs separated by grooves. The lugs protrude from the bottom of the grooves. The lugs contribute to the exertion of traction. Working machines such as agricultural machines and construction vehicles travel on unpaved roads such as wet fields and rough ground. In order to obtain high traction, lugged tires are mounted on working machines.

[0003] The lugged tire travels while being buried in mud. Mud adheres to the tread of the tire. When the working machine that has finished working moves to the next work site, for example, it travels on a general paved road. When traveling on a general paved road with mud still adhering to the tire, the mud falls off. As a result, the general paved road becomes dirty. There is a demand for a tire to which mud does not easily adhere or a tire from which mud easily falls off even if it adheres, so as not to stain the general paved road with mud. The following Patent Document 1 proposes providing a group of protrusions at the bottom of the lug in order to suppress the adhesion of mud.

Prior Art Documents

Patent Documents

[0004] [[ID=I27]] <oo00021>

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a lugged tire that can suppress the temperature rise of the lugs, suppress the adhesion of mud, and easily remove the mud even if it adheres.

Means for Solving the Problems

[0006] The lugged tire according to the present invention comprises a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass, and a pair of sidewalls located axially outward of the carcass. The tread comprises a plurality of lugs arranged circumferentially and separated by grooves. Each of the plurality of lugs protrudes from the bottom of the grooves. Each lug comprises a front end located on the equatorial plane of the tire and a rear end located on the end side of the tread and having a side surface. When the tire moves forward, the front end is located on the first side in the rotational direction, and the rear end is located on the rear side in the rotational direction. The lug comprises a plurality of radially arranged steps on its side surface. Each of the plurality of steps comprises a stepped portion and a stepped plate portion located radially outward of the stepped portion. The axial inner end of the stepped portion is the starting point of the step. The boundary between the stepped portion and the stepped plate portion is the edge of the step. The protruding reference line is a straight line passing through the edge of the tread and a position on the outer surface of the tire corresponding to the maximum width position of the carcass. Of the plurality of steps, the edge of the outermost step located radially outward is located axially outward from the protruding reference line, and the starting point of the innermost step located radially inward is located axially inward from the protruding reference line. The edges of the steps are inclined with respect to the circumferential direction. The tip of the edge located on the rotational leading side is located radially inward from the rear end of the edge located on the rotational trailing side. [Effects of the Invention]

[0007] According to the present invention, a lugged tire can be obtained that suppresses the temperature rise of the lugs, suppresses the adhesion of mud and dirt, and allows the mud and dirt to be easily removed even if they do adhere. [Brief explanation of the drawing]

[0008] [Figure 1] This is an exploded view showing a portion of the tread surface of a lugged tire according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along line II-II in Figure 1. [Figure 3]This is a plan view showing a portion of the side of the tire in Figure 1. [Figure 4] This is a cross-sectional view along line IV-IV in Figure 3. [Figure 5] This is a cross-sectional view showing a modified step. [Modes for carrying out the invention]

[0009] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0010] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

[0011] In this invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state.

[0012] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured at the tire's cross-section, obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a standard rim. The tire's structure, which cannot be confirmed when the tire is mounted on a standard rim, is confirmed at the aforementioned cross-section.

[0013] A genuine rim refers to a rim defined in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are all considered genuine rims.

[0014] Regular tire pressure refers to the internal pressure specified in the tire's standard. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are all considered regular tire pressures.

[0015] The standard load refers to the load specified in the tire's specifications. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are all considered standard loads.

[0016] In this invention, the tread portion of a tire is the part of the tire that makes contact with the road surface. The bead portion is the part of the tire that is fitted onto the rim. The sidewall portion is the part of the tire that spans the space between the tread portion and the bead portion. The tire comprises the tread portion, a pair of bead portions, and a pair of sidewall portions. The tread portion is the part that includes the tread as a component. The sidewall portion is the part that includes the sidewall as a component. The bead portion is the part that includes the bead as a component.

[0017] [Practices that formed the basis of this invention] In soft, moist fields, lugged tires will sink into the mud as they drive. Therefore, mud accumulation is unavoidable. The repeated deformation and recovery of rubber generates heat. Lugs are raised ridges that extend from the equatorial plane towards the edge of the tread. The lug height is greatest at the edge of the tread. The higher the lug height, the larger the volume of the lug. Lugs with high lug height tend to get hotter. In many cases, indentations are provided on the sides of the lugs to suppress the temperature rise. The recess has a configuration in which the periphery is surrounded by walls like a window frame. As described above, the lugged tire travels while being buried in mud and dirt. Mud and dirt get stuck in the recess. Providing the recess promotes the adhesion of mud and dirt. It is not easy to drop the mud and dirt that has once got stuck in the recess.

[0018] Therefore, the inventor has studied the shape of the side surface of the lug in order to obtain a lugged tire that suppresses the temperature rise of the lug, suppresses the adhesion of mud and dirt, and can easily drop the mud and dirt even if it adheres, and has completed the invention described below.

[0019] [Summary of Embodiment of the Present Invention] The present invention is a tire including a pair of beads, a carcass bridging between the pair of beads, a tread positioned radially outside the carcass, and a pair of sidewalls positioned axially outside the carcass, wherein the tread includes a plurality of lugs separated by grooves and arranged in the circumferential direction, the plurality of lugs each project from the bottom of the groove, the lug includes a tip portion positioned on the equatorial plane of the tire and a rear end portion positioned on the end side of the tread and including the side surface of the lug, when the tire advances, the tip portion is positioned on the leading side in the rotational direction and the rear end portion is positioned on the trailing side in the rotational direction, the lug includes a plurality of steps arranged radially on the side surface, each of the plurality of steps includes a step portion and a step plate portion positioned radially outside the step portion, the axially inner end of the step portion is the starting point of the step, the boundary between the step portion and the step plate portion is the edge of the step, a straight line passing through the end of the tread and a position on the outer surface of the tire corresponding to the maximum width position of the carcass is a protruding reference line, among the plurality of steps, the edge of the outermost step positioned radially outermost is positioned axially outside the protruding reference line, the starting point of the innermost step positioned radially innermost is positioned axially inside the protruding reference line, and the edge of the step is inclined with respect to the circumferential direction. A lugged tire in which the tip of the edge positioned on the leading side in the rotational direction is positioned radially inside the rear end of the edge positioned on the trailing side in the rotational direction.

[0020] The lugged tire of the present invention suppresses the temperature rise of the lugs, suppresses the adhesion of mud and dirt, and even if mud and dirt do adhere, they can be easily removed. The mechanism by which these effects are achieved is not yet clear, but it is presumed to be as follows.

[0021] When a tire is driven with the lugs buried in mud, a mud flow is generated from the equatorial plane towards the edge of the tread. This mud flow suppresses the adhesion of mud between the lugs arranged in the circumferential direction. This mud flow also extends to the sides of the lugs, and even if mud adheres to the sides of the lugs, this mud flow will dislodge the attached mud. The sides of the lugs have a shape that becomes more concave axially inward as it moves radially inward. This creates a gap between the side and the mud even if the lug is buried in mud, suppressing mud adhesion. The groove-like indentations formed by the steps promote heat dissipation, so the temperature rise of the lugs is suppressed, similar to when indentations are provided on the sides of the lugs as in conventional tires. Because the radially aligned steps act as the starting point for lug bending, the lugs of this tire are more flexible than those of conventional tires. The amount of recovery when the lugs return to their original shape is greater than that of conventional lugs, so when the bent lugs return to their original shape, the mud and dirt attached to the lugs are effectively shaken off. The stepped portion of the step slopes in the same direction as the edge of the step. As the tire rotates, the stepped portion scoops up mud, but because the leading edge of the stepped portion is located radially inward from the trailing edge, the mud that has accumulated on the stepped portion slides off due to the action of its own weight and inertia as the tire rotates. The sloping stepped portion can help suppress the adhesion of mud. These lugged tires suppress the temperature rise of the lugs, prevent mud from sticking to them, and allow mud to be easily removed even if it does stick.

[0022] Preferably, the ratio of the tread thickness to the tread width at the edge of the outermost step is 10% to 25%. This creates a sufficiently large gap between the side and the mud when the lug is buried in mud, effectively suppressing mud adhesion.

[0023] Preferably, the angle of the corner including the starting point of the step is between 90 degrees and 150 degrees. This allows the lugged tire to effectively prevent mud from getting stuck in the groove-like depressions that extend along the step, and even if mud does adhere to it, it can be effectively removed.

[0024] Preferably, the ratio of the length of the stepped portion to the thickness of the tread at the edge of the outermost step is 15% to 30%. This creates a sufficiently large gap between the side and the mud when the lug is buried in mud, effectively suppressing mud adhesion. This suppresses damage caused by the weight of the attached mud.

[0025] Preferably, at the rear end of the edge of the step, the angle that the edge makes with respect to the circumferential direction is between 10 degrees and 70 degrees. This allows the self-weight and inertial force to act more effectively on the mud on the stepped surface compared to when the angle is set to 0 degrees. The lugged tire can effectively slide the mud off the stepped surface.

[0026] Preferably, the corner including the starting point of the step and the corner including the edge of the step are rounded. This suppresses the concentration of distortion at the starting point and edge of the step. Lugged tires can suppress the occurrence of damage caused by the presence of the starting point and edge of the step. The steps provided on the side can fully perform their function.

[0027] The lugged tire of the present invention suppresses the temperature rise of the lugs, suppresses the adhesion of mud, and allows for easy removal of mud even if it does adhere. This lugged tire is suitably used as a lugged tire for agricultural machinery, where the lugs are often buried in mud during operation. From this viewpoint, it is preferable that the tire is for agricultural machinery.

[0028] According to the present invention, a lugged tire can be obtained that suppresses the temperature rise of the lugs, suppresses the adhesion of mud and dirt, and allows for easy removal of any mud and dirt that does adhere. This will be explained in detail below using the lugged tire shown in Figure 1 as an example.

[0029] [Details of the Embodiments of the Invention] Figures 1 and 2 show a part of a lugged tire 2 (hereinafter also simply referred to as "tire 2") according to one embodiment of the present invention. This tire 2 is mounted on agricultural machinery such as agricultural tractors, agricultural cultivators, rough terrain transport vehicles, and agricultural implements. This tire 2 is suitable for driving on soft roads and fields such as farmland.

[0030] Figure 1 is a plan view (i.e., unfolded view) of the tread surface 4 of tire 2. Figure 1 shows the tread pattern of tire 2.

[0031] The direction indicated by the double arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2. In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2. The direction indicated by the double arrow CD represents the circumferential direction of tire 2. The circumferential direction of tire 2 coincides with the direction of rotation of tire 2. The direction indicated by arrow CD1 is the leading side in the rotational direction when tire 2 moves forward, and the direction indicated by arrow CD2 is the trailing side in the rotational direction. As tire 2 moves forward in the field, it makes contact with the road surface from the leading side to the trailing side.

[0032] In Figure 1, the dashed line EL extending in the circumferential direction represents the equatorial plane of tire 2 (hereinafter also referred to as the tire equatorial plane). The position indicated by the symbol TE is the edge of the tread surface 4. In this invention, the edge TE of the tread surface 4 is also referred to as the edge of the tread.

[0033] Figure 2 shows a portion of the cross-section of tire 2 along the line II-II in Figure 1. The cross-section representing the internal structure of tire 2 shown in Figure 2 corresponds to the cross-section of tire 2 along the plane containing the rotation axis of tire 2 (hereinafter referred to as the meridian cross-section). The direction indicated by the double arrow RD is the radial direction of tire 2. The direction indicated by arrow RD1 is the radially inward direction of tire 2, and the direction indicated by arrow RD2 is the radially outward direction of tire 2. The position indicated by the symbol Eq is the equator of tire 2. Equator Eq is the intersection of the equatorial plane and the tread surface 4, and is the radial outer edge of tire 2.

[0034] In Figure 2, tire 2 is mounted on rim R. Rim R is a standard rim. For example, air is filled inside tire 2, and the internal pressure is adjusted. Although not shown in the diagram, a tube is inserted inside tire 2, and air is filled inside this tube. Tire 2 is a tube type. Tire 2 may also be a tubeless type.

[0035] The tire 2 comprises a tread 6, a pair of sidewalls 8, a pair of beads 10, and a carcass 12.

[0036] The tread 6 is located radially outward of the carcass 12. The tread 6 is in contact with the road surface. The outer surface of the tread 6 includes the aforementioned tread surface 4. Tread 6 is made of cross-linked rubber. Without going into detail, Tread 6 is made of cross-linked rubber commonly used for the treads of agricultural machinery tires.

[0037] The tread 6 comprises a plurality of lugs 16 separated by grooves 14. The plurality of lugs 16 are arranged in the circumferential direction. The lugs 16 protrude outward from the bottom 18 of the grooves 14. The top surfaces 20 of the lugs 16 are included in the tread surface 4. The tread surface 4 includes the top surfaces 20 of the plurality of lugs 16 provided on the tread 6. The portion of the tread surface 4 other than the top surfaces 20 is the groove 14.

[0038] The ratio of the total area of ​​the top surfaces 20 of the multiple lugs 16 included in the tread surface 4 to the area of ​​the tread surface 4 is the land ratio. This land ratio is determined in the unfolded view of the tread surface 4. The land ratio of this tire 2 is 50% or less. The land ratio of this tire 2 is smaller than that of a lugless tire, such as a passenger car tire.

[0039] In Figure 2, the dashed line TBL represents the virtual outer surface of the tread 6, assuming that the tread 6 does not have lugs 16. The bottom 18 of the groove 14 is included in the virtual outer surface TBL.

[0040] Lug 16 includes the edge TE of tread surface 4, in other words, the edge TE of tread 6. The lug 16 has a side surface 22 that extends radially inward from the edge TE of the tread 6. The edge TE of the tread 6 is the boundary between the top surface 20 of the lug 16 and its side surface 22. When the corner formed by the top surface 20 and the side surface 22 is rounded, as in the lug 16 of this tire 2, the edge TE of the tread 6 is represented by the intersection of the extension line LT of the top surface 20 and the extension line LS of the side surface 22, as shown in Figure 2.

[0041] Of the left and right tread ends TE of the tread 6, the end TE indicated by symbol TE1 is also called the first end, and the end TE indicated by symbol TE2 is also called the second end. In the tread 6 shown in Figure 1, one end TE located in the direction indicated by arrow AD1 is the first end TE1. The other end TE located in the direction indicated by arrow AD2 is the second end TE2. The end TE located in the direction indicated by arrow AD1 may be called the second end TE2, and the end TE located in the direction indicated by arrow AD2 may be called the first end TE1.

[0042] In Figure 2, the length indicated by the double arrow TW is the width of the tread 6. The width of the tread 6 TW is the axial distance from one end TE of the tread 6 to the other end TE of the tread 6. The width of the tread 6 TW is determined in a tire 2 in a normal state.

[0043] As mentioned above, the tread 6 of this tire 2 has multiple lugs 16. Each of the multiple lugs 16 has a leading end 24 located on the equatorial plane and a trailing end 26 located on the edge TE side of the tread 6. The aforementioned side surface 22 is included in the trailing end 26 of the lug 16. The trailing end 26 comprises the side surface 22 of the lug 16.

[0044] The lug 16 extends from the leading edge 24 toward the trailing edge 26. In the circumferential direction, the leading edge 24 is located on the side of the trailing edge 26 that makes contact with the road surface. When the tire 2 moves forward, the leading edge 24 is located on the side of the rotational direction that makes contact with the road surface, and the trailing edge 26 is located on the side of the rotational direction that makes contact with the road surface. In the running state of the tire 2, the lug 16 makes contact with the road surface from the leading edge 24 toward the trailing edge 26.

[0045] The lugs 16 of this tire 2 include a plurality of first lugs 28 located in the zone between the equatorial plane and the first end TE1 of the tread 6 (hereinafter also called the first zone), and a plurality of second lugs 30 located in the zone between the equatorial plane and the second end TE2 of the tread 6 (hereinafter also called the second zone).

[0046] Multiple first lugs 28 are arranged in the first zone at predetermined intervals in the circumferential direction. The first lugs 28 extend from the equatorial plane toward the first end TE1 of the tread 6. Multiple second lugs 30 are arranged in the second zone at predetermined intervals in the circumferential direction. The second lugs 30 extend from the equatorial plane toward the second end TE2 of the tread 6. The first lug 28 and the second lug 30 are arranged alternately in the circumferential direction. The first lug 28 and the second lug 30 alternately contact the road surface.

[0047] Each sidewall 8 is connected to the tread 6. The sidewall 8 is located radially inward of the tread 6. The sidewall 8 is located axially outward of the carcass 12.

[0048] Sidewall 8 is made of cross-linked rubber. Although not described in detail, sidewall 8 is made of cross-linked rubber commonly used for the sidewalls of agricultural machinery tires. Sidewall 8 may be made of the same cross-linked rubber as tread 6, or it may be made of a different cross-linked rubber.

[0049] Each bead 10 is located radially inward of the sidewall 8. The bead 10 comprises a core 32 and an apex 34. The core 32 extends in the circumferential direction. Although not shown, the core 32 includes steel wires. The apex 34 is located radially outward from the core 32. The apex 34 is made of cross-linked rubber with high rigidity.

[0050] As previously mentioned, the tire 2 comprises a pair of beads 10. For convenience of explanation, in this specification, the bead 10 located on the first end TE1 side of the tread 6 is called the first bead 10a, and the bead 10 located on the second end TE2 side is also called the second bead 10b. Alternatively, the bead 10 located on the first end TE1 side may be called the second bead 10b, and the bead 10 located on the second end TE2 side may be called the first bead 10a.

[0051] The carcass 12 is located inside the tread 6 and a pair of sidewalls 8. The carcass 12 spans between a pair of beads 10.

[0052] The carcass 12 comprises at least one carcass ply 36. The carcass 12 of this tire 2 comprises two carcass plies 36. Of the two carcass plies 36 that make up the carcass 12, the carcass ply 36 located radially inward on the radially inward side of the tread 6 is also called the inner ply 38, and the carcass ply 36 located radially outward is also called the outer ply 40. This carcass 12 may comprise three or more carcass plies 36.

[0053] Each of the two carcass plies 36 is folded over at its respective bead 10. The carcass plies 36 of this tire 2 are folded over at each bead 10 from the axially inward to the axially outward direction. The carcass plies 36 are roll-up plies. This carcass 12 comprises two roll-up plies.

[0054] Although not shown, each carcass ply 36 contains a number of parallel carcass cords. In each carcass ply 36, the carcass cords are inclined with respect to the equatorial plane. This carcass 12 has a bias structure. In this tire 2, the direction of inclination of the carcass cords in the inner ply 38 and the direction of inclination of the carcass cords in the outer ply 40 are opposite to each other.

[0055] Carcass cords are cords made of organic fibers (hereinafter referred to as organic fiber cords). Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0056] In Figure 2, the length indicated by the double arrow RM represents the thickness of the tread 6 at the edge TE of the tread 6. The thickness of the tread 6 is expressed as the length from the carcass 12 to the outer surface of the tread 6, measured along the normal to the outer surface of the carcass 12. If the outer surface of the carcass 12 cannot be identified, the carcass line, which is included in the carcass 12 and represented by the outermost carcass cord, is used as the outer surface of the carcass 12. The tread 6 of this tire 2 exhibits its maximum thickness RM at the edge TE of the tread 6. As previously mentioned, the lug 16 includes the edge TE of the tread 6. The protrusion height of the lug 16 is maximum at the edge TE of the tread 6.

[0057] Figure 3 shows the side view 22 of lug 16. In Figure 3, arrow DR indicates the direction of rotation of tire 2 when it moves forward. The direction perpendicular to the plane of paper in Figure 3 is the axial direction of tire 2.

[0058] The lugs 16 of the tire 2 have a plurality of steps 42 on their side surface 22. The plurality of steps 42 are arranged radially. Of the plurality of steps 42, the step 42 located radially on the outermost side is called the outermost step 42s, and the step 42 located radially on the innermost side is called the innermost step 42u.

[0059] Each of the multiple steps 42 comprises a stepped portion 44 and a step plate portion 46. The step plate portion 46 is located radially outward from the stepped portion 44. In Figure 2, the position indicated by the symbol SS is the axial inner end of the stepped portion 44. In this invention, the axial inner end SS of the stepped portion 44 is the starting point of step 42. The starting point SS of the adjacent step 42, located radially outward from step 42, is the ending point of step 42. The ending point of the outermost step 42s is the edge TE of the tread 6. The starting point SSu of the innermost step 42u is included in the outer surface 2G of the tire 2. The aforementioned virtual outer surface TBL of the tread 6 connects to the outer surface 2G of the tire 2 at the starting point SSu.

[0060] As described above, the side surface 22 of the lug 16 is provided with a plurality of steps 42 arranged radially. This creates a recess on the side surface 22 with the starting point SS of the step 42 as the bottom. The side surface 22 of the lug 16 is provided with a plurality of recesses arranged radially.

[0061] In Figure 2, the position indicated by the symbol SG is the boundary between the stepped portion 44 and the stepped plate portion 46. The boundary SG is the axial outer end of the stepped portion 44 and the radial inner end of the stepped plate portion 46. In step 42, the step plate portion 46 is connected to the step portion 44 at its axial outer end SG. In other words, in step 42, the step portion 44 is connected to the step plate portion 46 at its radial inner end SG. In the present invention, the boundary SG between the step portion 44 and the step plate portion 46 is the edge of step 42. The step portion 44 and the step plate portion 46 constitute a corner including the edge SG of step 42.

[0062] In Figure 2, the position indicated by the symbol CW is the position where the carcass 12 exhibits its maximum width (hereinafter referred to as the carcass maximum width position). The position indicated by the symbol PW is the intersection of a straight line extending axially through the carcass maximum width position CW and the outer surface 2G of the tire 2. In this invention, this intersection PW is the carcass maximum width corresponding position. If there are decorations such as patterns or letters on the outer surface 2G, the carcass maximum width corresponding position PW is determined based on a virtual outer surface obtained by assuming there are no decorations. The solid line LWE is a straight line passing through the edge TE of the tread 6 and the position PW corresponding to the maximum width of the carcass. In this invention, this straight line LWE is the protruding reference line.

[0063] As mentioned above, the tread 6 has multiple lugs 16 arranged in the circumferential direction, and each of the multiple lugs 16 has a leading end 24 located on the equatorial plane and a trailing end 26 located on the edge TE side of the tread 6. When the tire 2 moves forward, the lugs 16 make contact with the road surface from the leading end 24 to the trailing end 26. When the tire 2 runs with the lugs 16 buried in mud, a flow of mud is generated from the equatorial plane toward the edge TE of the tread 4. This flow of mud suppresses the adhesion of mud between the circumferentially arranged lugs 16. This flow of mud also extends to the sides 22 of the lugs 16. Even if mud adheres to the sides 22 of the lugs 16, this flow of mud will remove the attached mud.

[0064] As mentioned above, the lug 16 has a plurality of steps 42 arranged radially on its side surface 22. As shown in Figure 2, of the plurality of steps 42, the edge SGs of the outermost step 42s located radially outward is located axially outward from the protruding reference line LWE, and the starting point SSu of the innermost step 42u located radially inward is located axially inward from the protruding reference line LWE. The side surface 22 of the lug 16 has a shape that becomes recessed axially inward as it moves radially inward. As a result, even if the lug 16 is buried in mud, a gap is created between the side surface 22 and the mud, suppressing the adhesion of mud. The groove-like recesses formed by the steps 42 promote heat dissipation, so the temperature rise of the lug 16 is suppressed, similar to when recesses are provided on the side surface 22 of the lug 16 as in conventional tires. Since the radially aligned steps 42 function as the starting point for bending of the lug 16, the lug 16 of this tire 2 is more flexible than the lug of a conventional tire. Because the amount of recovery when the lug 16 returns to its original position is greater than that of a conventional lug, when the bent lug 16 returns to its original position, the mud and dirt adhering to the lug 16 are effectively shaken off.

[0065] As shown in Figure 3, the edge SG of step 42 is inclined with respect to the circumferential direction. The edge SG of step 42 has a leading end Gh located on the rotational leading side and a trailing end Gt located on the rotational trailing side, with the leading end Gh of edge SG being located radially inward from the trailing end Gt of edge SG. The stepped portion 44 of step 42 is inclined in the same direction as the edge SG of step 42. The first side of the stepped portion 44 is located radially inward from the second side. As the tire 2 rotates, the stepped portion 44 scoops up mud, but as the tire 2 rotates, the mud on the stepped portion 44 slides off due to the action of its own weight and inertia. The inclined stepped portion 44 can help suppress the adhesion of mud.

[0066] This tire 2 suppresses the temperature rise of the lugs 16, suppresses the adhesion of mud, and allows mud to be easily removed even if it does adhere.

[0067] As shown in Figure 2, among the multiple steps 42 provided on the side surface 22 of the lug 16, the edges SGs of the outermost step 42s located radially to the outermost side are the axial outer ends of the tire 2. The length indicated by the double arrow RX in Figure 2 is the thickness of the tread 6 at the edges SGs of the outermost step 42s.

[0068] In this tire 2, the ratio RX / TW of the thickness RX of the tread 6 at the edge SGs of the outermost step 42s to the width TW of the tread 6 is preferably between 10% and 25%. By setting the ratio RX / TW to 10% or more, a gap of an effective size is formed between the side surface 22 of the lug 16 and the mud. Even when the tire 2 is driven with the lug 16 buried in the mud, the adhesion of the mud is suppressed. From this viewpoint, a ratio RX / TW of 15% or more is more preferable. By setting the ratio RX / TW to 25% or less, when the tire 2 is driven over a field with ridges, for example, contact between the lugs 16 and the ridges is suppressed. The tire 2 is prevented from damaging the ridges while driving. From this viewpoint, a ratio RX / TW of 20% or less is more preferable.

[0069] Figure 4 shows a cross-section along the line IV-IV in Figure 3. The line IV-IV in Figure 3 is a straight line extending radially in Figure 3. Figure 4 shows a portion of the meridian cross-section of this tire 2.

[0070] The stepped portion 44 of the first step 42 and the stepped plate portion 46 of the step 42 located next to this first step form a corner including the starting point SS of step 42. In Figure 4, angle α is the angle formed by the stepped portion 44 of the first step 42 and the stepped plate portion 46 of the step 42 located next to this first step. In the present invention, this angle α is the narrow angle of the corner including the starting point SS of step 42. The narrow angle α of the corner including the starting point SSu of the innermost step 42u is represented by the angle formed by the stepped portion 44 of the innermost step 42u and the tangent to the outer surface 2G of the tire 2 at the starting point SSu of this innermost step 42u.

[0071] In this tire 2, it is preferable that the angle α of the corner including the starting point SS of step 42 is between 90 degrees and 150 degrees. By setting the angle α to 90 degrees or more, the occurrence of damage caused by stress concentration at the starting point SS of step 42 is suppressed, and the settling of mud into the depression formed by step 42 is also suppressed. From this viewpoint, it is more preferable that the angle α be 105 degrees or more. By setting the angle α to 150 degrees or less, the arrangement of multiple radially aligned steps 42 on the side surface 22 effectively contributes to the deflection of the lug 16. When the deflected lug 16 returns to its original position, the mud adhering to the lug 16 is effectively shaken off. From this viewpoint, it is more preferable that the angle α be 135 degrees or less.

[0072] In Figure 4, the length indicated by the double arrow β is the length of the stepped portion 44. In this tire 2, the ratio β / RX of the length β of the stepped portion 44 to the thickness RX of the tread 6 at the edge SG of the outermost step 42s is preferably 15% or more and 30% or less. By setting the ratio β / RX to 15% or more, a gap of an effective size is formed between the side surface 22 of the lug 16 and the mud. Even when the tire 2 is driven with the lug 16 buried in the mud, the adhesion of the mud is suppressed. From this viewpoint, a ratio β / RX of 20% or more is more preferable. By setting the ratio β / RX to 30% or less, the occurrence of damage caused by the weight of the attached mud is suppressed. From this perspective, a ratio β / RX of 25% or less is more preferable.

[0073] In Figure 3, the dashed line LA represents the trajectory of the rear end Gt of the edge SG of step 42 on the rotating tire 2. This trajectory is represented by a circle centered on the rotation axis of tire 2. The solid line LP is the tangent line at the rear end Gt of the edge SG of step 42 to the circle representing the trajectory of the rear end Gt of the edge SG of step 42. The angle γ is the angle between this tangent line LP and the edge SG of step 42. In this invention, this angle γ is the angle that the edge SG makes with respect to the circumferential direction at the rear end Gt of the edge SG of step 42.

[0074] In this tire 2, the angle γ that the edge SG makes with respect to the circumferential direction at the rear end Gt of the edge SG of step 42 is preferably between 10 degrees and 70 degrees. As a result, when the tire 2 rotates, the mud that has accumulated on the stepped portion 44 slides off easily due to the action of its own weight and inertial force. Mud adhesion is suppressed. From this viewpoint, it is more preferable that the angle γ is between 45 degrees and 70 degrees.

[0075] As mentioned above, in this tire 2, multiple steps 42 are provided radially on the side surface 22 of the lug 16. In other words, the number of steps 42 provided on the side surface 22 is two or more. The more steps 42 provided on the side surface 22, the more easily the lug 16 can bend. When the bent lug 16 returns to its original shape, the mud and dirt adhering to the lug 16 are effectively shaken off. From this viewpoint, it is preferable that the number of steps 42 provided on the side surface 22 be three or more, and more preferably four or more. Since a larger number of steps 42 is preferable, no preferred upper limit is set for the number of steps 42. The upper limit for the number of steps 42 that can be provided on the side surface 22 is set appropriately, taking into consideration the size of the side surface 22, the aforementioned narrowing angle α, and the length β of the stepped portion 44.

[0076] When there are three or more steps 42 on the side surface 22, the larger the angle γ, the easier it is for the mud on the stepped portion 44 to slide off due to the action of its own weight and inertial force. From this viewpoint, it is preferable that there are three or more steps 42 on the side surface 22 and the angle γ is between 45 degrees and 70 degrees, and it is more preferable that there are four or more steps 42 on the side surface 22 and the angle γ is between 30 degrees and 60 degrees.

[0077] Figure 5 shows a modified example of the step 42 provided on the side surface 22 of the lug 16. Figure 5, like the cross-section in Figure 4, shows a portion of the meridian cross-section of this tire 2.

[0078] In step 42 shown in Figure 5, the corner including the starting point SS of step 42 and the corner including the edge SG of step 42 are rounded. This suppresses the concentration of strain on the starting point SS and edge SG of step 42. This tire 2 can suppress the occurrence of damage caused by the presence of the starting point and edge of step 42. Step 42 provided on the side surface 22 of lug 16 can fully perform its function. From this viewpoint, it is preferable that the corner including the starting point SS of step 42 and the corner including the edge SG of step 42 are rounded.

[0079] In Figure 5, arrow Rs represents the rounding radius of the corner including the starting point SS of step 42. Arrow Rg represents the rounding radius of the corner including the edge SG of step 42. From the viewpoint of effectively suppressing the concentration of strain at the starting point SS of step 42, it is preferable that the rounding radius Rs of the corner including the starting point SS of step 42 is 2 mm or more and 10 mm or less. From the viewpoint of effectively suppressing the concentration of strain at the edge SG of step 42, it is preferable that the rounding radius Rg of the corner including the edge SG of step 42 is 1 mm or more and 5 mm or less. The radius Rs of the corner rounding including the starting point SS of step 42 and the radius Rg of the corner rounding including the edge SG of step 42 may be the same, but from the viewpoint of effectively suppressing the occurrence of damage caused by the presence of the starting point SS and edge SG of step 42, it is preferable that the radius Rs of the corner rounding including the starting point SS of step 42 is larger than the radius Rg of the corner rounding including the edge SG of step 42. In this case, it is preferable that the difference between radius Rs and radius Rg (Rs-Rg) is 1 mm or more and 5 mm or less.

[0080] As is clear from the above description, according to the present invention, a lugged tire 2 is obtained that suppresses the temperature rise of the lugs, suppresses the adhesion of mud, and allows the mud to be easily removed even if it adheres. The present invention can be suitably used as a lugged tire for agricultural machinery, which is often driven with the lugs 16 buried in mud. [Industrial applicability]

[0081] The technologies described above—which suppress lug temperature rise, inhibit mud adhesion, and allow for easy removal of mud if it does adhere—can be applied to various tires mounted on work machinery such as agricultural machinery and construction vehicles.

[0082] [Note] The present invention includes the following embodiments.

[0083] [1] A tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass, and a pair of sidewalls located axially outward of the carcass, wherein the tread comprises a plurality of lugs arranged circumferentially separated by grooves, each of the plurality of lugs protruding from the bottom of the grooves, and each lug comprises a front end located on the equatorial plane of the tire and a rear end located on the end of the tread and having the side surface of the lug, and when the tire moves forward, the front end is located on the first side in the rotational direction and the rear end is located on the second side in the rotational direction, and the lug comprises a plurality of radially arranged steps on the side surface, each of the plurality of steps comprising a stepped portion and a front A lugged tire comprising: a stepped plate portion located radially outward of a stepped portion, wherein the axial inner end of the stepped portion is the starting point of the step, the boundary between the stepped portion and the stepped plate portion is the edge of the step, a straight line passing through the edge of the tread and a position on the outer surface of the tire corresponding to the maximum width position of the carcass is a projection reference line, the edge of the outermost step located radially outward of the projection reference line is located axially outward of the projection reference line, the starting point of the innermost step located radially inward is located axially inward of the projection reference line, the edge of the step is inclined with respect to the circumferential direction, and the tip of the edge located on the rotational leading side is located radially inward of the rear end of the edge located on the rotational trailing side. [2] The lugged tire according to [1] above, wherein the ratio of the thickness of the tread to the width of the tread at the edge of the outermost step is 10% or more and 25% or less. [3] A lugged tire as described in [1] or [2] above, wherein the angle of the corner including the starting point of the step is 90 degrees or more and 150 degrees or less. [4] A lugged tire according to any one of the above [1] to [3], wherein the ratio of the length of the stepped portion to the thickness of the tread at the edge of the outermost step is 15% or more and 30% or less. [5] A lugged tire according to any of [1] to [4] above, wherein the angle that the edge makes with respect to the circumferential direction at the rear end of the edge of the step is 10 degrees or more and 70 degrees or less. [6] A lugged tire according to any of the above [1] to [5], wherein the corner including the starting point of the step and the corner including the edge of the step are rounded. [7] A lugged tire for agricultural machinery, as described in any of the above [1] through [6]. [Explanation of Symbols]

[0084] 2... Tires 4. Tread surface 6...Tread 8. Sidewall 10, 10a, 10b...bead 12...Carcass 14...Groove 16...rug 18...Bottom of groove 14 20... Top surface of lug 16 22...side of lug 16 24...Tip of lug 16 26...Rear end of lug 16 42, 42s, 42u... steps 44... Step section 46...Step board section

Claims

1. A tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass, and a pair of sidewalls located axially outward of the carcass, The tread comprises a plurality of lugs separated by grooves and arranged in the circumferential direction, Each of the lugs protrudes from the bottom of the groove, The lug comprises a leading end located on the equatorial plane of the tire and a rear end located on the edge of the tread and having a side surface of the lug, When the tire moves forward, the leading edge is positioned towards the front end in the direction of rotation, and the rear end is positioned towards the rear end in the direction of rotation. The lug has a plurality of steps arranged radially on its side surface, Each of the aforementioned steps comprises a stepped portion and a stepped plate portion located radially outward from the stepped portion, The axial inner end of the stepped portion is the starting point of the step. The boundary between the stepped portion and the stepped plate portion is the edge of the step. The straight line passing through the edge of the tread and the position on the outer surface of the tire corresponding to the maximum width position of the carcass is the protruding reference line. Of the multiple steps, the edge of the outermost step located radially outward is located axially outward from the protruding reference line, and the starting point of the innermost step located radially inward is located axially inward from the protruding reference line. The edge of the aforementioned step is inclined with respect to the circumferential direction, The tip of the edge located on the side that arrives first in the direction of rotation is located radially inward from the rear end of the edge located on the side that arrives second in the direction of rotation. Lug tires.

2. The ratio of the thickness of the tread to the width of the tread at the edge of the outermost step is 10% or more and 25% or less. A lugged tire as described in claim 1.

3. The angle of the corner including the starting point of the aforementioned step is 90 degrees or more and 150 degrees or less. A lugged tire as described in claim 1.

4. The ratio of the length of the stepped portion to the thickness of the tread at the edge of the outermost step is 15% or more and 30% or less. A lugged tire as described in claim 1.

5. At the rear end of the edge of the step, the angle that the edge makes with respect to the circumferential direction is 10 degrees or more and 70 degrees or less. A lugged tire as described in claim 1.

6. The corner including the starting point of the step and the corner including the edge of the step are rounded. A lugged tire as described in claim 1.

7. It is for agricultural machinery. A lugged tire according to any one of claims 1 to 6.

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