JP2014177230A - Pneumatic tire for agricultural machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for an agricultural machine capable of preventing the occurrence of heel-and-toe abrasion, while restraining reduction in traction performance and clogging of mud.SOLUTION: The tire comprises a plurality of lugs 2 slantingly extending to a meridian plane, and has an aspect ratio of 65-90%, and assuming a radius of curvature of a lug surface 2a as (r) in an equatorial plane, a circumferential directional curve length of the lug surface 2a as L, and a circumferential directional curve length of the lug surface 2a between a circumferential directional end A on the stepping-in side of the lug and a point B projecting most to the outside in the radial direction as aL, an actual tread surface of the lug is formed of a smooth curve in an area between a circumferential directional contour line of connecting the circumferential directional end A and the point B when a ratio X of a radial directional height T1 from the lug groove bottom of the circumferential directional end A to a radial directional height T2 from the lug groove bottom of the point B takes 1-0.5a, and a circumferential directional contour line of connecting the circumferential directional end A and the point B when the ratio X takes 1-0.1a.

Description

この発明は、トラクター等の農業機械に適用される、トレッド表面に複数のラグを具える空気入りタイヤに関するものであり、とくには、トラクション機能の低下や、ラグ間への泥詰りの発生を抑制するとともに、ラグへのヒールアンドトゥ摩耗の発生を有効に防止できる技術を提案するものである。   The present invention relates to a pneumatic tire having a plurality of lugs on a tread surface, which is applied to an agricultural machine such as a tractor, and particularly suppresses a decrease in traction function and mud clogging between lugs. In addition, the present invention proposes a technique that can effectively prevent the occurrence of heel and toe wear on the lug.

農業機械用の空気入りタイヤでは、圃場等で耕転機械その他を索引するためにトラクション性能が重要な性能となっている。
しかるに、圃場等では土がラグ間の溝に詰まる、いわゆる泥詰りが発生し易く、この泥詰りによって、ラグの圃場等の刺さり込みが困難になるため、トラクション性能の低下が余儀なくされることになる。 In pneumatic tires for agricultural machines, traction performance is an important performance for indexing tilling machines and the like in the field.
However, soil is clogged in the grooves between the lugs, so-called mud clogging is likely to occur in farm fields, etc., and this mud clogging makes it difficult to penetrate the rug fields etc. Become.

そこで、ラグ溝の泥詰りを防いで高いトラクション性能を維持するため、農業機械用空気入りタイヤでは、トレッド幅方向の中央から側部にかけて、タイヤ子午面に対して傾斜して延在するとともに、トレッド幅方向のそれぞれの半部で相互に逆向きに傾斜する複数本のラグをトレッド表面に設け、トレッド表面の展開視で、複数本のラグの表面積の総和の、トレッド幅とトレッド周長との積に対する比率を２５％程度とすることが広く一般に行われている。   Therefore, in order to prevent mud clogging of the lug groove and maintain high traction performance, in the pneumatic tire for agricultural machinery, it extends from the center to the side in the tread width direction while being inclined with respect to the tire meridian surface, Provided on the tread surface a plurality of lugs inclined in opposite directions in each half of the tread width direction, and in the development view of the tread surface, the total surface area of the plurality of lugs, tread width and tread circumference It is widely practiced to set the ratio to the product of approximately 25%.

ところが、トレッド表面にこのようなラグを設けた場合は、ラグの踏込端部に比してブレーキング力が相対的に大きくなるラグの蹴出端部で剪断力が大きくなって、該蹴出端部の摩耗量が多くなる現象が生じる。
これがため、ラグの踏込端部と蹴出端部との間に接地圧の不均衡が生じて、踏込端部の接地圧が蹴出端部のそれより高くなって、ラグの蹴出端部が、踏込端部に比して滑り易くなる。それ故に、滑り易くなった蹴出端部の摩耗が促進されて、ラグに、ヒールアンドトゥ摩耗と称される偏摩耗が発生することになる。 However, when such a lug is provided on the tread surface, the shearing force becomes larger at the kicking end of the lug where the braking force is relatively larger than the stepping end of the lug. A phenomenon occurs in which the amount of wear at the end increases.
For this reason, an imbalance of the ground pressure occurs between the stepping end of the lug and the kicking end, the grounding pressure of the stepping end becomes higher than that of the kicking end, and the lug kicking end However, it becomes easier to slip than the stepped-in end. Therefore, the wear of the kicking end that has become slippery is promoted, and uneven wear called heel and toe wear occurs in the lug.

このようにヒールアンドトゥ摩耗が発生すると、タイヤの外観が悪化するだけではなく、トラクション性能の低下、タイヤの摩耗寿命の低下、車両の振動の発生原因となる。   When the heel and toe wear occurs in this way, not only the appearance of the tire is deteriorated, but also the traction performance, the tire wear life and the vehicle vibration are caused.

これに対し、特許文献１には、ブロックパターンを有する空気入りタイヤのブロックへのヒールアンドトゥ摩耗の発生を抑制する技術が、また特許文献２には、ラグパターンを有する空気入りタイヤのラグの均一摩耗をもたらす技術がそれぞれ開示されている。   In contrast, Patent Document 1 discloses a technique for suppressing the occurrence of heel and toe wear on a block of a pneumatic tire having a block pattern, and Patent Document 2 discloses uniform wear of a lug of a pneumatic tire having a lug pattern. Each of the technologies that provide the above is disclosed.

特開平６−１６６３０４号公報JP-A-6-166304 特表２００１−５２２３３３号公報JP 2001-522333 A

しかしながら、特許文献２に開示された技術は、異なるラグの摩耗速度の均一化を目指すものであり、単一ラグ内の偏摩耗を改善するものではなく、また、特許文献１に開示された技術は、単一陸部内のヒールアンドトゥ摩耗の抑制効果を高めるものではあるも、単一ラグではなく、単一ブロックのヒールアンドトゥ摩耗を抑制するものである。   However, the technique disclosed in Patent Document 2 aims to make the wear rate of different lugs uniform, and does not improve the uneven wear in a single lug. Also, the technique disclosed in Patent Document 1 Although it increases the suppression effect of heel and toe wear in a single land portion, it suppresses heel and toe wear of a single block instead of a single lug.

この発明は、特許文献１に開示された技術に改良を加えたものであり、それの目的とするところは、トラクション性能の低下や、ラグ間のラグ溝への泥詰りの発生を抑制しつつ、ラグへのヒールアンドトゥ摩耗の発生を効果的に防止できる農業機械用空気入りタイヤを提供することにある。   The present invention is an improvement on the technique disclosed in Patent Document 1, and the object of the present invention is to suppress the deterioration of traction performance and the occurrence of mud clogging in lug grooves between lugs. Another object of the present invention is to provide a pneumatic tire for agricultural machinery that can effectively prevent heel and toe wear on the lug.

この発明の農業機械用空気入りタイヤは、トレッド幅方向の中央部から側部にかけて、タイヤ子午面、すなわち、タイヤの子午線に沿う大円面に対して傾斜して延在するとともに、トレッド幅方向のそれぞれの半部で相互に逆向きに傾斜する複数本のラグをトレッド表面に具え、扁平率が６５〜９０％の範囲のものであって、タイヤの中心軸線と直交する赤道面内で、各ラグ表面の、仮想のトレッド周方向輪郭線の曲率半径をｒ、ラグ表面の、仮想のトレッド周方向曲線長さをＬ、タイヤの外径半径を、前記曲率半径ｒより大きいＲＴ、タイヤのラグ溝底の半径をＲＢ、ラグの踏込側の周方向端Ａと、ラグ表面が半径方向外側に最も凸となる点Ｂとの間の、ラグ表面の、仮想のトレッド周方向長さをａＬ（ただし、０．５≦ａ≦１．０とする）としたときに、ラグの前記周方向端Ａのラグ溝底からの半径方向高さＴ１の、前記点Ｂのラグ溝底からの半径方向高さＴ２に対する比Ｘ（＝Ｔ１／Ｔ２）の値が１−０．５ａをとる場合の、前記周方向端Ａと点Ｂとを結ぶ仮想のトレッド周方向輪郭線と、比Ｘの値が１−０．１ａをとる場合の、前記周方向端Ａと点Ｂとを結ぶ仮想のトレッド周方向輪郭線との間の領域内で、前記ラグの実際のトレッド表面を滑らかな曲線で形成してなるものである。   The pneumatic tire for agricultural machinery according to the present invention extends from the central part to the side part in the tread width direction so as to be inclined with respect to the tire meridian surface, that is, the great circular surface along the meridian of the tire, and in the tread width direction A plurality of lugs inclined in opposite directions in each half of the tread surface, the flatness is in the range of 65 to 90%, and in the equator plane perpendicular to the center axis of the tire, The radius of curvature of the virtual tread circumferential contour line of each lug surface is r, the virtual tread circumferential curve length of the lug surface is L, the outer radius of the tire is RT larger than the curvature radius r, The radius of the lug groove bottom is RB, and the virtual tread circumferential length of the lug surface between the circumferential end A on the lug stepping side and the point B where the lug surface is most convex outward in the radial direction is aL (However, 0.5 ≦ a ≦ 1.0 The value of the ratio X (= T1 / T2) of the radial height T1 from the lug groove bottom at the circumferential end A of the lug to the radial height T2 from the lug groove bottom at the point B Imaginary tread circumferential contour line connecting the circumferential edge A and the point B when the ratio is 1-0.5a, and the circumferential edge when the ratio X is 1-0.1a The actual tread surface of the lug is formed by a smooth curve in a region between a virtual tread circumferential contour line connecting A and the point B.

かかるタイヤにおいて好ましくは、トレッド表面の展開視で、各ラグがタイヤ子午面に対してなす角度θを２０〜５０°の範囲とする。   In such a tire, an angle θ formed by each lug with respect to the tire meridian plane in a development view of the tread surface is preferably set in a range of 20 to 50 °.

また好ましくは、トレッド表面の展開視で、複数本のラグの表面積の総和の、トレッド幅とトレッド周長との積に対する比率Ｙを２０〜４０％の範囲とする。   Preferably, the ratio Y of the sum of the surface areas of the plurality of lugs to the product of the tread width and the tread circumference is 20 to 40% in a developed view of the tread surface.

ここにおいて、「トレッド幅」とは、タイヤを適用リムに装着するとともに、そこに規定の空気圧を充填した無負荷状態のタイヤ姿勢の下での、一方のトレッド端から他方のトレッド端までの曲線長さをいうものとし、「トレッド周長」とは、タイヤを適用リムに装着するとともに、そこに規定の空気圧を充填した無負荷状態のタイヤ姿勢での、タイヤ赤道線上での周長の他、トレッド幅方向の各位置で、同様のタイヤ姿勢の下で測った周長をいうものとする。
なお、上記の「トレッド端」とは、タイヤを適用リムに装着するとともに、規定の空気圧を充填し、平板に対してキャンバー角０°で垂直に置いて規定の負荷を作用させたタイヤ姿勢で、平板での接触面の、タイヤの中心軸線方向の最外側の接地位置をいうものとする。
この場合、「適用リム」とは、タイヤのサイズに応じて下記の規格に規定されたリムを、「規定の空気圧」とは、下記の規格において最大負荷能力に対応して規定される空気圧をいい、「規定の負荷」とは、最大負荷能力をいうものとする。
なお、最大負荷能力とは、下記の規格で、タイヤに負荷することが許容される最大の質量をいう、
ところで、ここでいう空気圧は、窒素ガス等の不活性ガスその他の圧力とすることも可能である。
そして規格とは、タイヤが生産または使用される地域に有効な産業規格によって決められたものであり、たとえば、アメリカ合衆国では、“THE TIRE and RIM ASSOCIATION INC.のYEAR BOOK”であり、欧州では、“THE European Tyre and Rim Technical OrganisationのSTANDARDS MANUAL”であり、日本では日本自動車タイヤ協会の“JATMA YEAR BOOK”である。 Here, the “tread width” is a curve from one tread end to the other tread end under an unloaded tire posture in which a tire is mounted on an applicable rim and filled with a specified air pressure. “Tread circumference” refers to the length of the tire on the equator when the tire is mounted on the applicable rim and filled with the specified air pressure. The circumference measured under the same tire posture at each position in the tread width direction.
The above-mentioned “tread end” means a tire posture in which a tire is mounted on an applicable rim, filled with a prescribed air pressure, placed perpendicular to a flat plate with a camber angle of 0 ° and subjected to a prescribed load. The outermost contact position of the contact surface on the flat plate in the direction of the center axis of the tire is assumed to be.
In this case, “applicable rim” refers to the rim specified in the following standards according to the tire size, and “specified air pressure” refers to the air pressure specified in accordance with the maximum load capacity in the following standards. “Regular load” means the maximum load capacity.
The maximum load capacity is the maximum mass that is allowed to be applied to the tire in the following standards.
By the way, the air pressure referred to here may be an inert gas such as nitrogen gas or other pressure.
The standard is determined by an industrial standard effective in the region where the tire is produced or used. For example, in the United States, “THE TIRE and RIM ASSOCIATION INC. YEAR BOOK”, in Europe, “ It is “STANDARDS MANUAL” of THE European Tire and Rim Technical Organization, and “JATMA YEAR BOOK” of Japan Automobile Tire Association in Japan.

そしてまた好ましくは、トレッド幅方向の中央部での、ラグの踏込側の周方向端の高さＨの、ラグ幅Ｗに対する比（Ｈ／Ｗ）を、
０．５＜Ｈ／Ｗ＜３．０
とする。なお、ラグの踏込側の周方向端の高さとは、ラグの溝底からラグの実際のトレッド表面における踏込側の周方向端に至る高さをいい、また、ラグ幅とは、トレッド幅方向の中央部において、ラグの延在する向きに対して直交する向きの長さをいう。 And preferably, the ratio (H / W) of the height H of the circumferential end on the lug stepping side to the lug width W at the center in the tread width direction,
0.5 <H / W <3.0
And Note that the height of the circumferential end on the stepping side of the lug means the height from the groove bottom of the lug to the circumferential end of the stepping side on the actual tread surface of the lug, and the lug width is the direction of the tread width. The length of the direction perpendicular to the direction in which the lug extends in the center portion of.

この発明の空気入りタイヤでは、トレッド表面に設けたラグの表面の、仮想のトレッド周方向輪郭線の曲率半径ｒを、タイヤの外径ＲＴより小さく設定し、前記点Ｂを、ラグの中央位置（ａ＝０．５のとき）から、前記周方向端Ａとは反対側の、ラグの蹴出端（ａ＝１．０のとき)までの間に位置させ、さらに、ラグの実際のトレッド表面を滑らかな曲線で形成するとともに、点Ｂとの関係において周方向端Ａのラグ溝底からの半径方向高さＴ１を適正なものとしているので、タイヤの新品時および摩耗初期の接地圧の最大位置は、ラグ表面が半径方向外側に最も凸となる点Ｂとなる。   In the pneumatic tire of the present invention, the radius of curvature r of the virtual tread circumferential contour line on the surface of the lug provided on the tread surface is set smaller than the outer diameter RT of the tire, and the point B is set at the center position of the lug. (When a = 0.5) to the lug kicking end (when a = 1.0) opposite to the circumferential end A, and the actual tread of the lug The surface is formed with a smooth curve, and the radial height T1 from the bottom of the lug groove at the circumferential end A in relation to the point B is made appropriate. The maximum position is a point B where the lug surface is most convex outward in the radial direction.

これがため、空気入りタイヤが負荷転動すると、接地圧の低い部分である前記周方向端Ａが、前記点Ｂに比して路面に対して多く滑ることになって、ラグの踏込み側の周方向端Ａ側の摩耗の進展速度が点Ｂより大きくなる。それ故に、摩耗の初期から摩耗の中期にかけてのヒールアンドトゥ摩耗の進展を効果的に遅らせることができる。   For this reason, when the pneumatic tire rolls under load, the circumferential end A, which is a portion with a low ground pressure, slides more on the road surface than the point B, and the lug on the stepping side of the lug is reduced. The progress rate of wear on the direction end A side becomes larger than the point B. Therefore, the progress of heel and toe wear from the initial stage of wear to the middle stage of wear can be effectively delayed.

ところで、このタイヤにおいて、比Ｘ（＝Ｔ１／Ｔ２）の値を１−０．５ａと、１−０．１ａとに場合分けするのは、比Ｘが（１−０．１ａ）を越えると、従来の空気入りタイヤのラグ（タイヤ外径ＴＲと、ラグ表面の、仮想のトレッド周方向輪郭線の曲率半径ｒとが同一のもの）と同等になってしまって、この発明に由来する効果が小さく、一方、比Ｘが（１−０．５ａ）未満では、ラグの蹴出側周方向端が極端に低い接地圧となって滑り易くなり、タイヤの摩耗の初期から極端なヒールアンドトゥ摩耗が進行することになるからである。   By the way, in this tire, the value of the ratio X (= T1 / T2) is divided into 1-0.5a and 1-0.1a when the ratio X exceeds (1-0.1a). The effect derived from the present invention is equivalent to a conventional pneumatic tire lug (the tire outer diameter TR and the radius of curvature r of the virtual tread circumferential contour on the lug surface are the same). On the other hand, when the ratio X is less than (1-0.5a), the lug kick-out side circumferential end becomes extremely low in contact with the ground and becomes slippery, resulting in extreme heel and toe wear from the beginning of tire wear. Because it will progress.

このようなタイヤにおいて、トレッド表面の展開視で、各ラグがタイヤ子午面に対してなす角度θを２０〜５０°の範囲としたときは、農業機械用タイヤとして、必要なトラクション性能を発揮させつつ、ラグ溝に付着した泥を効果的に排出させることができる。
いいかえれば、ラグ角度が２０°未満では、ラグ溝内の泥を効果的に排出することが難しく、一方、当該角度が５０°を越えると、ラグが畑地等に刺さり込んで回転することによって発生する力がトレッド幅方向に逃げることになって、トラクション性態の低下が余儀なくされることになる。 In such a tire, when the angle θ formed by each lug with respect to the meridian of the tire is in the range of 20 to 50 ° in the development view of the tread surface, the necessary traction performance is exhibited as an agricultural machine tire. Meanwhile, the mud adhering to the lug groove can be effectively discharged.
In other words, if the lag angle is less than 20 °, it is difficult to effectively drain mud in the lag groove. On the other hand, if the angle exceeds 50 °, the lag is caused by sticking into the field and rotating. The force to do escapes in the tread width direction, and the traction property is inevitably lowered.

また、複数本のラグの表面積の総和の、トレッド幅とトレッド周長との積に対する比率Ｙを２０〜４０％の範囲とした場合は、タイヤの圃場等での負荷転動に当り、所要のトラクション性能を確保しつつ、ラグ溝に付着した泥の円滑なる排出を担保することができる。
すなわち、比率Ｙが４０％を越えると、ラグ溝幅が狭くなりすぎて泥詰りの発生のおそれが高くなり、一方、２０％未満では、必然的にラグの本数が少なくなりすぎて、所要のトラクション性能の確保が難しくなり、加えて摩耗ボリュームが減少して摩耗ライフが短くなるからである。 In addition, when the ratio Y of the total surface area of the plurality of lugs to the product of the tread width and the tread circumference is in the range of 20 to 40%, the load rolling on the tire field etc. It is possible to ensure smooth discharge of mud adhering to the lug groove while ensuring traction performance.
That is, if the ratio Y exceeds 40%, the lug groove width becomes too narrow and the risk of mud clogging increases. On the other hand, if the ratio Y is less than 20%, the number of lugs inevitably decreases, and the required This is because it is difficult to ensure the traction performance, and in addition, the wear volume is reduced and the wear life is shortened.

さらに、比率Ｙを２０〜４０％の範囲とした上で、トレッド幅方向の中央部での、ラグの踏込側の周方向端の高さＨの、ラグ幅Ｗに対する比（Ｈ／Ｗ）を、
０．５＜Ｈ／Ｗ＜３．０
としたときは、所要の摩耗性能及び泥排出性能を確保した上で、トラクション性能及び圃場等以外の道（舗装路、砂利道等）を走行する際の振動乗り心地を損なうことがない。
すなわち、上述した比率Ｙを２０〜４０％の範囲とするためには、所定のラグ幅に抑える必要があるところ、Ｈ／Ｗの値が０．５以下となる場合は、ラグの大きさが小さくなりすぎて、摩耗ボリュームの減少によって摩耗ライフが短くなるからであり、Ｈ／Ｗの値が３．０以上となる場合は、ラグの高さが高くなりすぎてその剛性が著しく低下するため、摩耗速度が増加して摩耗ライフが短くなる他、ヒールアンドトゥ摩耗を助長して、トラクション性能の低下、タイヤの摩耗寿命の低下、車両の振動の発生原因となるからである。 Furthermore, after setting the ratio Y in the range of 20 to 40%, the ratio (H / W) of the height H of the circumferential end on the lug stepping side to the lug width W at the center in the tread width direction ,
0.5 <H / W <3.0
In such a case, while ensuring the required wear performance and mud discharge performance, the traction performance and the vibration riding comfort when traveling on roads other than fields (paved roads, gravel roads, etc.) are not impaired.
That is, in order to make the above-mentioned ratio Y in the range of 20 to 40%, it is necessary to suppress to a predetermined lug width. When the value of H / W is 0.5 or less, the size of the lug is This is because the wear life is shortened by reducing the wear volume because the wear volume is too small. When the H / W value is 3.0 or more, the height of the lug becomes too high and the rigidity thereof is significantly lowered. This is because the wear rate is increased and the wear life is shortened, and heel-and-toe wear is promoted, resulting in a decrease in traction performance, a decrease in tire wear life, and generation of vehicle vibration.

この発明の実施形態の、タイヤ中心軸線と直交する赤道面内での各部の寸法関係を示す図である。It is a figure which shows the dimensional relationship of each part in the equator plane orthogonal to a tire center axis line of embodiment of this invention. ラグの、仮想の周方向断面を示す図である。It is a figure which shows the virtual circumferential cross section of a lug. 図２の変更例を示す図２と同様の断面図である。FIG. 3 is a cross-sectional view similar to FIG. 2 showing a modified example of FIG. 2. トレッド表面の展開視を示す図である。It is a figure which shows the development view of the tread surface. トレッド幅方向の中央部でのラグ寸法を示す図である。It is a figure which shows the lug dimension in the center part of a tread width direction. ラグの、仮想の周方向中央部に、ラグ表面が半径方向外側に最も凸となる点Ｂを有する、実施例タイヤ１および２のヒールアンドトゥ摩耗による段差部体積を示すグラフである。It is a graph which shows the level | step-difference part volume by the heel and toe wear of the Example tires 1 and 2 which has the point B where the lug surface becomes the most convex on the radial direction outer side in the virtual circumferential direction center part. ラグの蹴出端に、ラグ表面が半径方向外側に最も凸となる点Ｂを有する、実施例タイヤ３および４のヒールアンドトゥ摩耗による段差部体積を示すグラフである。図である。It is a graph which shows the level | step-difference part volume by the heel and toe wear of Example tire 3 and 4 which has the point B where the lug surface becomes the most convex on the radial direction outer side at the kicking end of a lug. FIG.

以下にこの発明の実施形態を図面に示すところに基いて説明する。
この発明の農業機械用空気入りタイヤは、図５に示すところから明らかなように、トレッド幅方向の中央部から側部にかけて、タイヤ子午面、すなわち、タイヤ１の子午線ｍ−ｍに沿う大円面に対して傾斜して延在するとともに、トレッド幅方向のそれぞれの半部で相互に逆方向に傾斜する複数本のラグ２をトレッド表面に具え、扁平率が６５〜９０％の範囲のものである。 Embodiments of the present invention will be described below based on the drawings.
As is apparent from FIG. 5, the pneumatic tire for agricultural machinery according to the present invention is a great circle along the meridian of the tire, that is, the meridian mm of the tire 1 from the center to the side in the tread width direction. A plurality of lugs 2 extending in an inclined manner with respect to the surface and inclined in opposite directions at the respective halves of the tread width direction on the tread surface, with a flatness in the range of 65 to 90% It is.

そしてこのタイヤでは、タイヤの中心軸線と直交するタイヤ赤道面内で、各ラグ２の表面２ａの、仮想のトレッド周方向輪郭線の曲率半径を、図１〜３に例示するｒ、ラグ表面２ａの、仮想のトレッド周方向曲線長さをＬとし、タイヤ１の外径半径を、図１に例示するように、曲率半径ｒより大きいＲＴ、タイヤ１のラグ２間のラグ溝３のラグ溝底の半径を、これも図１に例示するようにＲＢとし、また、ラグ２の踏込側の周方向端Ａと、ラグ表面２ａが半径方向外側に最も凸となる点Ｂとの間のラグ表面２ａの、仮想のトレッド周方向曲線長さをａＬ（ただし、０．５≦ａ≦１．０とする）としたときに、ラグ２の前記周方向端Ａのラグ溝底からの半径方向高さＴ１の、前記点Ｂのラグ溝底からの半径方向高さＴ２に対する比Ｘ（＝Ｔ１／Ｔ２）の値が１−０．５ａをとる場合の、前記周方向端Ａと点Ｂとを結ぶ仮想のトレッド周方向輪郭線と、比Ｘの値が１−０．１ａをとる場合の、前記周方向端Ａと点Ｂとを結ぶ仮想のトレッド周方向輪郭線との間の領域内で、前記ラグの実際のトレッド表面を滑らかな曲線で形成する。   In this tire, the radius of curvature of the virtual tread circumferential contour line of the surface 2a of each lug 2 in the tire equator plane orthogonal to the center axis of the tire is illustrated in FIGS. The imaginary tread circumferential curve length is L, and the outer radius of the tire 1 is RT larger than the radius of curvature r and the lug groove of the lug groove 3 between the lugs 2 of the tire 1 as illustrated in FIG. As shown in FIG. 1, the bottom radius is RB, and the lug between the stepping side circumferential end A of the lug 2 and the point B where the lug surface 2a is most convex outward in the radial direction. Radial direction from the lug groove bottom of the circumferential end A of the lug 2 when the virtual tread circumferential curve length of the surface 2a is aL (provided that 0.5 ≦ a ≦ 1.0) Ratio X of height T1 to radial height T2 from the bottom of the lug groove at point B (= T1 / When the value of 2) takes 1-0.5a, the virtual tread circumferential contour line connecting the circumferential end A and the point B, and the ratio X takes 1-0.1a, The actual tread surface of the lug is formed with a smooth curve in a region between a virtual tread circumferential contour line connecting the circumferential end A and the point B.

このように構成してなるタイヤでは、ａの値は０．５〜１．０の範囲にあるので、比Ｘが１−０．５ａをとる場合は、比Ｘは、０．５〜０．７５の範囲の値となし、比Ｘが１−０．１ａをとる場合は、比Ｘは、０．９〜０．９５の範囲の値となる。   In the tire configured as described above, since the value of a is in the range of 0.5 to 1.0, when the ratio X is 1-0.5a, the ratio X is 0.5 to 0.00. When the value is in the range of 75 and the ratio X is 1 to 0.1a, the ratio X is in the range of 0.9 to 0.95.

また、図２に示す空気入りタイヤ１では、ラグ表面２ａがタイヤ半径方向外側に最も凸となる点Ｂが、ラグ２の仮想の周方向中央部に位置することになって、ａ＝０．５となり、比Ｘは、０．７５もしくは０．９５となる。図示のＴ２の寸法を１とすると、Ｔ１は０．７５（Ｔ１ｍｉｎ）または０．９５（Ｔ１ｍａｘ）となる。
なおここでは、ラグ２の点Ｂが、ラグ２の周方向中央に存在し、リブ表面２ａが半径方向外方に凸となる滑らかな曲線で形成されているので、タイヤ１の新品時および、摩耗の初期の接地圧は、ラグ２の該中央部で最大となり、タイヤ１の負荷転動に当って接地圧が相対的に低くなる、ラグの踏込側の周方向端Ａは、ラグ２の前記中央部よりも路面等に対して滑り易くなる。
このことによって、ラグ２の前記周方向端Ａの摩耗の進行速度を大きくすることで、タイヤ１の摩耗の初期から摩耗の中期に到る間のヒールアンドトゥ摩耗の進展を有効に遅らせることができる。 In the pneumatic tire 1 shown in FIG. 2, the point B at which the lug surface 2a is most convex outward in the radial direction of the tire is located at the virtual circumferential central portion of the lug 2 so that a = 0. 5 and the ratio X is 0.75 or 0.95. When the dimension of T2 shown in the figure is 1, T1 is 0.75 (T1min) or 0.95 (T1max).
Here, the point B of the lug 2 exists at the center of the lug 2 in the circumferential direction, and the rib surface 2a is formed with a smooth curve that protrudes radially outward. The ground contact pressure at the initial stage of wear becomes maximum at the central portion of the lug 2, and the ground pressure becomes relatively low when the tire 1 is subjected to load rolling. It becomes easier to slide with respect to the road surface or the like than the central portion.
Thus, by increasing the wear progressing speed of the circumferential end A of the lug 2, the progress of the heel and toe wear during the period from the initial wear of the tire 1 to the middle wear can be effectively delayed.

ところで、図３に示す空気入りタイヤ１のラグ２では、ラグ表面２ａが半径方向外側に最も凸となる点Ｂがラグ２の蹴出端Ｃと一致する。すなわち、ａ＝１．０になるので、図示のＴ２の寸法を１とすると、Ｔ１は、０．５（Ｔ１ｍｉｎ）または０．９（Ｔ１ｍａｘ）となる。
このラグ２では、ラグ表面２ａが半径方向外側に最も凸となる点Ｂがラグ２の蹴出端Ｃに一致することから、タイヤの新品時および摩耗の初期の接地圧は、ラグ２の蹴出端Ｃで最大となり、ラグ２の踏込側の周方向端Ａで相対的に低くなるので、踏込側周方向端Ａが蹴出端Ｃに比して滑り易くなる。
これがため、摩耗の初期においては、前記周方向端Ａの摩耗速度を図２に示すラグ２よりも一層大きくなって、蹴出端Ｃ側のゴム体積が踏込側周方向端Ａ側のゴム体積に比してより大きくなり、それ故に、摩耗の初期から中期に到る間のヒールアンドトゥ摩耗を、図２に示すラグ２よりもさらに遅らせることができる。 Incidentally, in the lug 2 of the pneumatic tire 1 shown in FIG. 3, the point B at which the lug surface 2 a is most convex outward in the radial direction coincides with the kicking end C of the lug 2. That is, since a = 1.0, when the dimension of T2 shown in the figure is 1, T1 is 0.5 (T1min) or 0.9 (T1max).
In this lug 2, the point B where the lug surface 2 a is most convex outward in the radial direction coincides with the kicking end C of the lug 2. Since the maximum is at the protruding end C and relatively low at the circumferential end A on the stepping side of the lug 2, the stepping-side circumferential end A is more slippery than the kicking end C.
Therefore, at the initial stage of wear, the wear rate at the circumferential end A is larger than that of the lug 2 shown in FIG. 2, and the rubber volume on the kicking end C side is the rubber volume on the stepping side circumferential end A side. Therefore, the heel and toe wear during the period from the beginning to the middle of the wear can be further delayed than the lug 2 shown in FIG.

以上に述べたような空気入りタイヤ１において、図４に示すようなトレッド表面の展開視で、各ラグ２がタイヤ子午面に対してなす傾き角度θを２０〜５０°の範囲とすることが、所要のトラクション性能を確保しつつ、ラグ溝３からのすぐれた排土機能を担保する上で好ましい。   In the pneumatic tire 1 as described above, the inclination angle θ formed by each lug 2 with respect to the tire meridian plane in a development view of the tread surface as shown in FIG. 4 may be in the range of 20 to 50 °. It is preferable for ensuring the excellent soil removal function from the lug groove 3 while ensuring the required traction performance.

またこのタイヤ１において、トレッド表面の展開視で、複数本のラグ２の表面積の総和の、トレッド幅とトレッド周長との積に対する比率Ｙを２０〜４０％の範囲とすることが、所要のトラクション性能および、所要の泥排出性能を実現する上で好ましい。   In the tire 1, the ratio Y of the total surface area of the plurality of lugs 2 to the product of the tread width and the tread circumferential length in a development view of the tread surface is in a range of 20 to 40%. It is preferable for realizing the traction performance and the required mud discharge performance.

そしてさらには、比率Ｙを２０〜４０％の範囲とした上で、図５に示すように、トレッド幅方向の中央部での、ラグの踏込側の周方向端の高さＨの、ラグ幅Ｗに対する比（Ｈ／Ｗ）を、
０．５＜Ｈ／Ｗ＜３．０
とすることが、所要の摩耗性能及び泥排出性能を確保した上で、トラクション性能及び舗装路、砂利道等を走行する際の振動乗り心地を維持できる点で好適である。 And furthermore, after making ratio Y into the range of 20 to 40%, as shown in FIG. 5, the lug width of the height H of the circumferential direction end by the side of the lug in the center part of the tread width direction The ratio to W (H / W)
0.5 <H / W <3.0
This is preferable in that the required wear performance and mud discharge performance can be secured, and the traction performance and the vibration riding comfort when traveling on a paved road, a gravel road, etc. can be maintained.

サイズが７１０／７０ Ｒ４２の、表１に示す諸元を有する実施例タイヤ１〜４および比較例タイヤ１〜６のそれぞれにつき、実車走行によって摩耗試験、トラクション試験および泥詰り量測定試験を行ったところ、表２に示す結果を得た。
なお、これらの試験は、各タイヤをＤＷ２３ＡＸ４２のリムに装着するとともに、タイヤへの充填空気圧を１６０ＫＰａとし、ＴＲＡに規定される、充填空気圧に対応する大きさの負荷を作用させた条件の下にて行い、
摩耗試験は、コンクリート路面上を４０ｋｍ／ｈの速度で２００００ｋｍ走行後の、ヒールアンドトゥ摩耗によって消失したラグのゴム体積を測定することにより行い、
トラクション試験は、圃場（泥地）を５ｋｍ／ｈの速度で走行したときのトラクション力を測定することにより行い、
泥詰り量測定試験は、トラクション試験の終了時にラグの溝内に付着した泥の重量を測定することにより行った。 For each of Example tires 1 to 4 and Comparative tires 1 to 6 having the dimensions shown in Table 1 and having a size of 710/70 R42, a wear test, a traction test, and a mud clogging measurement test were performed by running the vehicle. The results shown in Table 2 were obtained.
These tests were performed under the conditions in which each tire was mounted on the rim of DW23AX42, the filling air pressure to the tire was set to 160 KPa, and a load having a magnitude corresponding to the filling air pressure was applied as defined in TRA. Done,
The abrasion test is carried out by measuring the rubber volume of the lug that has disappeared due to heel and toe wear after traveling 20000 km at a speed of 40 km / h on the concrete road surface.
The traction test is performed by measuring the traction force when traveling in a field (muddy land) at a speed of 5 km / h.
The mud clogging measurement test was performed by measuring the weight of mud adhering in the groove of the lug at the end of the traction test.

なお試験結果は、比較例タイヤ１の結果をコントロールとする指数によって評価し、トラクション力は指数値が大きい方が、その他の試験結果は指数値が小さい方がすぐれた結果を示すものとした。
ところで、図２に示すラグ形態を有する実施例タイヤ１，２、および、図３に示すラグ形態を有する実施例タイヤ３，４のそれぞれの、ヒールアンドトゥ摩耗による段差部体積（指数）の、比Ｘに対する値を、図６および７のそれぞれにも併せて示す。 The test results were evaluated by an index using the results of Comparative Example Tire 1 as a control, and the traction force showed a better result when the index value was larger and the other test results were better when the index value was smaller.
By the way, the ratio X of the step portion volume (index) due to heel and toe wear of each of the example tires 1 and 2 having the lug shape shown in FIG. 2 and the example tires 3 and 4 having the lug shape shown in FIG. The values for are also shown in FIGS. 6 and 7, respectively.

表２に示すところによれば、実施例タイヤ１〜４はいずれも、トラクション力の低下および、泥付着量の増加をもたらすことなく、ヒールアンドトゥ摩耗を効果的に抑制できることが解かる。
そして、このヒールアンドトゥ摩耗の、比Ｘに対する抑制効果は、図６，７に示すところからより明確である。 According to the results shown in Table 2, it can be seen that all of the Example tires 1 to 4 can effectively suppress heel and toe wear without causing a decrease in traction force and an increase in the amount of mud adhesion.
And the suppression effect with respect to the ratio X of this heel and toe wear is clearer from the place shown to FIG.

１ タイヤ
２ ラグ
２ａ ラグ表面
３ ラグ溝
ｒ ラグ表面の曲率半径
Ｌ ラグ表面の周方向曲線長さ
ＲＴ タイヤの外径半径
ＲＢ ラグ溝底の半径
Ａ ラグの踏込側の周方向端
Ｂ ラグ表面が半径方向外側に最も凸となる点
Ｃ ラグの蹴出端
ａＬ Ａ，Ｂ間の周方向曲線長さ
Ｔ１ 周方向端Ａの半径方向高さ
Ｔ２ 点Ｂの半径方向高さ
Ｘ 比（＝Ｔ１／Ｔ２）
θ ラグの子午面に対する傾き角度
Ｙ （ラグの表面積の総和／トレッド幅×トレッド周長）の比率
Ｈ ラグの踏込側周方向端の高さ
Ｗ ラグ幅 1 tire 2 lug 2a lug surface 3 lug groove r radius of curvature of lug surface circumferential curve length RT of lug surface RT outer radius of tire RB radius A of lug groove bottom circumferential end B of lug stepping side Point C that is most convex outward in the radial direction C Circumferential curve length T1 between lug kicking ends aLA and B Radial height T2 of circumferential end A Radial height X ratio of point B (= T1 / T2)
θ Ratio of the angle of inclination Y of the lug relative to the meridian surface (total surface area of the lug / tread width × tread circumference) H The height of the lug on the circumferential side W The lug width

Claims (4)

トレッド幅方向の中央部から側部にかけて、タイヤ子午面に対して傾斜して延在するとともに、トレッド幅方向のそれぞれの半部で相互に逆向きに傾斜する複数本のラグをトレッド表面に具え、扁平率が６５〜９０％の範囲の農業機械用空気入りタイヤであって、
タイヤの中心軸線と直交する赤道面内で、各ラグ表面の、仮想のトレッド周方向輪郭線の曲率半径をｒ、ラグ表面の、仮想のトレッド周方向曲線長さをＬ、タイヤの外径半径を、前記曲率半径ｒより大きいＲＴ、タイヤのラグ溝底の半径をＲＢ、ラグの踏込側の周方向端Ａと、ラグ表面が半径方向外側に最も凸となる点Ｂとの間の、ラグ表面の、仮想のトレッド周方向曲線長さをａＬ（ただし、０．５≦ａ≦１．０とする）としたときに、ラグの前記周方向端Ａのラグ溝底からの半径方向高さＴ１の、前記点Ｂのラグ溝底からの半径方向高さＴ２に対する比Ｘ（＝Ｔ１／Ｔ２）の値が１−０．５ａをとる場合の、前記周方向端Ａと点Ｂとを結ぶ仮想のトレッド周方向輪郭線と、比Ｘの値が１−０．１ａをとる場合の、前記周方向端Ａと点Ｂとを結ぶ仮想のトレッド周方向輪郭線との間の領域内で、前記ラグの実際のトレッド表面を滑らかな曲線で形成してなる農業機械用空気入りタイヤ。 The tread surface is provided with a plurality of lugs extending from the center to the side in the tread width direction so as to be inclined with respect to the tire meridian surface and inclined in opposite directions in the respective half portions in the tread width direction. , A pneumatic tire for agricultural machinery having a flatness ratio of 65 to 90%,
Within the equator plane perpendicular to the tire center axis, the radius of curvature of the virtual tread circumferential contour line of each lug surface is r, the virtual tread circumferential curve length of the lug surface is L, and the tire outer radius is Between the radius R of the radius of curvature of the tire RB, the radius of the bottom of the lug groove of the tire RB, the circumferential end A on the stepping side of the lug, and the point B where the lug surface is most convex radially outward When the virtual tread circumferential curve length of the surface is aL (provided that 0.5 ≦ a ≦ 1.0), the radial height from the bottom of the lug groove at the circumferential end A of the lug When the value of the ratio X (= T1 / T2) of the point B to the radial height T2 from the lug groove bottom at the point B is 1-0.5a, the circumferential end A and the point B are connected. A virtual tread circumferential contour line and the circumferential end A and point B when the value of the ratio X is 1-0.1a In the region between the virtual tread circumferential direction contour line connecting the actual agricultural machinery pneumatic tire comprising forming the tread surface in a smooth curve of said lug. トレッド表面の展開視で、各ラグがタイヤ子午面に対してなす角度θを２０〜５０°の範囲としてなる請求項１に記載の空気入りタイヤ。   2. The pneumatic tire according to claim 1, wherein an angle θ formed by each lug with respect to the tire meridian plane in a development view of the tread surface is in a range of 20 to 50 °. トレッド表面の展開視で、複数本ラグの表面積の総和の、トレッド幅とトレッド周長との積に対する比率Ｙを２０〜４０％の範囲としてなる請求項１もしくは２に記載の空気入りタイヤ。   The pneumatic tire according to claim 1 or 2, wherein a ratio Y of a sum of surface areas of a plurality of lugs to a product of a tread width and a tread circumferential length is in a range of 20 to 40% in a developed view of the tread surface. トレッド幅方向の中央部での、ラグの踏込側の周方向端の高さＨの、ラグ幅Ｗに対する比（Ｈ／Ｗ）を、
０．５＜Ｈ／Ｗ＜３．０
としてなる請求項３に記載の空気入りタイヤ。 The ratio (H / W) with respect to the lug width W of the height H of the circumferential end of the lug stepping side at the center in the tread width direction,
0.5 <H / W <3.0
The pneumatic tire according to claim 3.

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