JP2017159752A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of effectively improving both steering stability and high speed durability.SOLUTION: A pneumatic tire has a tread part with thereon at least three major grooves extending in a tire circumferential direction and at least four rows of land parts 21 to 25 partitioned by the major grooves, and a direction in which the tire is to be attached to a vehicle is designated. On a meridian cross section, tread surfaces of the land parts are each projected in a tire radial direction outside a profile line TL in a tire width direction specified based on tread surface edge positions Pto Pof the land parts and ground end positions Pand Pof the tread part 1. Projection amounts T1 to T5 from the profile line of the tread surface of each land part are set to be 0.05 to 0.2 mm, and at least one of thin grooves 42 to 44 extending in the tire circumferential direction is provided on each land part. The groove widths GW2 to GW4 of the thin grooves are set to be 2 to 20% of the widths RW2 to RW4 of the land parts on which the thin grooves are provided, and the groove widths of the thin grooves are narrower toward the outside of the vehicle from the inside thereof.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire having at least three main grooves extending in the tire circumferential direction in a tread portion and at least four rows of land portions defined by the main grooves, and more particularly, steering stability and high-speed durability. It is related with the pneumatic tire which enabled it to improve effectively.

  In a pneumatic tire, a plurality of main grooves extending in the circumferential direction are provided in a tread portion, and a plurality of rows of land portions based on land portions (that is, ribs) continuous in the tire circumferential direction are partitioned by these main grooves. There is. In such a pneumatic tire, the contact pressure at the edge portion of each land portion is relatively high, and the contact pressure tends to be uneven within the land portion. And when driving | running in the state where the contact pressure in the edge part of each land part is relatively high, there exists a problem that the contact length in the center part of each land part reduces, and steering stability falls.

  In order to solve such a problem, it is proposed to optimize the installation state of each land portion by bulging the tread surface of the land portion defined by the main groove in the tread portion toward the outer side in the tire radial direction. (For example, see Patent Documents 1 to 3).

  However, for example, in the case of a pneumatic tire intended for high-speed running, since the camber angle when mounted on a vehicle is normally set to negative, in the pneumatic tire in which the tread surface of the land portion bulges as described above, When the vehicle is mounted, the ground pressure becomes excessive inside the vehicle, and excessive heat generation occurs during high-speed driving, resulting in rubber deterioration such as reversion, and failure is likely to occur (that is, high speed There is a problem that durability deteriorates). Therefore, in a pneumatic tire with a tread on the land, the high speed endurance is good even when it is set as a negative camber while obtaining the effect (improvement of steering stability) due to the swelling of the tread on the land. There is a need for measures to improve performance.

JP 2004-122904 A JP 2002-029216 A JP 2005-263180 A

  SUMMARY OF THE INVENTION An object of the present invention is a pneumatic tire having at least three main grooves extending in the tire circumferential direction in a tread portion and at least four rows of land portions defined by the main grooves. It is an object of the present invention to provide a pneumatic tire that can effectively improve the above.

  In order to achieve the above object, a pneumatic tire according to the present invention includes a tread portion that extends in the tire circumferential direction to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and the sidewall portions. A pair of bead portions disposed on the inner side in the tire radial direction, the tread portion has at least three main grooves extending in the tire circumferential direction and at least four rows of land portions defined by the main grooves, The tread portion has a profile line in a tire width direction specified based on an edge position of the land portion and a contact end position of the tread portion in a meridian cross section, and a pneumatic tire in which a mounting direction with respect to a vehicle is designated In the meridian section, the tread of the land portion protrudes outward in the tire radial direction from the profile line. The amount of protrusion from the file line is 0.05 mm or more and 0.2 mm or less, and each land portion has at least one narrow groove extending in the tire circumferential direction, and the groove width of the narrow groove is The groove of the narrow groove that is 2% or more and 20% or less of the width of the land portion provided, and that extends from the inside of the vehicle that is on the inside of the vehicle to the outside of the vehicle when the vehicle is mounted. The width is reduced.

  In the present invention, as described above, since the tread of the land portion protrudes in the tire radial direction from the profile line, the contact shape can be improved, and in particular, the contact length of each land portion can be expanded. Excellent handling stability can be obtained. At this time, since the land portion protruding from the profile line is provided with a narrow groove extending in the tire circumferential direction, the rubber amount of the land portion is reduced, and the ground pressure is excessive due to the land portion protruding. It can suppress and can improve high-speed durability. In particular, since the groove width of the narrow groove is reduced from the inside of the vehicle to the outside of the vehicle, the tendency of the contact pressure in the negative camber (the contact pressure on the inside of the vehicle is relatively high and the contact pressure on the outside of the vehicle is relatively low) ), It is possible to appropriately suppress excessive contact pressure in each land portion, and to further improve high-speed durability. On the other hand, since the groove width of the narrow groove is limited as described above, it is possible to prevent the land portion rigidity from being significantly lowered by providing the narrow groove, and the effect of the narrow groove (improvement of high-speed durability) ) And the effect (improvement of steering stability) by projecting the land portion can be balanced.

  In the present invention, when the amount of protrusion from the profile line of the tread surface of the land portion is 0.05 mm or more and less than 0.5 mm, the groove width of the narrow groove is 2% or more of the width of the land portion provided with the narrow groove 5 When the protrusion amount from the profile line of the tread of the land portion is 0.5 mm or more and less than 1.0 mm, the groove width of the narrow groove is 5% or more of the width of the land portion provided with the narrow groove. The width of the narrow groove is 10% of the width of the land portion where the narrow groove is provided when the protrusion amount from the profile line of the tread surface is less than 10% and not more than 1.0 mm. It is preferable that it is 20% or less. Thus, by setting the groove width of the narrow groove according to the amount of protrusion from the profile line of the tread of the land part, the rubber amount and rigidity of each land part can be optimized, and high speed durability can be improved. This is advantageous in achieving both handling stability and maintenance.

  In the present invention, the groove depth of the narrow groove is preferably 20% to 50% of the groove depth of the main groove having the smallest groove depth among the main grooves. Thus, by setting the groove depth of the narrow groove, it is possible to prevent an excessive decrease in the rigidity of the land portion, which is advantageous in maintaining steering stability.

  In the present invention, it is preferable that the narrow groove is disposed at a position where the tread surface of the land portion protrudes most from the profile line. By arranging the narrow grooves in this way, excessive ground pressure can be accurately suppressed, which is advantageous for improving high-speed durability.

  In the present invention, the “ground contact end” is an end portion in the tire axial direction when a normal load is applied by placing the tire on a normal rim and filling the normal internal pressure vertically on a plane. The length in the tire axial direction between the ground contact ends on both sides in the tire width direction is a “ground contact width”, and a region specified by the ground contact width is a “ground contact region”. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO. Then, “Measuring Rim” is set. “Regular internal pressure” is the air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is for JATA and the table “TIRE ROAD LIMITS AT VARIOUS” is for TRA. The maximum value described in “COLD INFRATION PRESURES”, “INFLATION PRESURE” for ETRTO, but 180 kPa when the tire is a passenger car. “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFORATION PRESSURES” is “LOAD CAPACITY” if it is ETRTO, but if the tire is a passenger car, the load is equivalent to 88% of the load.

  Further, the profile line of the tread part is specified based on the edge position of the land part and the ground end position of the tread part. For example, if the land portion on the inner side in the tire width direction from the outermost main groove in the tire width direction is the center land portion and the land portion on the outer side in the tire width direction from the outermost main groove in the tire width direction is the shoulder land portion, the center land The profile line in the section has three points on the tire meridian cross section: the edge position on both sides of the center land portion and the edge position on the side close to the center land portion of the other center land portion adjacent to the center land portion. And is depicted by an arc having a center on the inner side in the tire radial direction. In addition, the profile line in the shoulder land portion includes a ground end position of the shoulder land portion, an edge position facing the main groove of the shoulder land portion, and a center land portion adjacent to the shoulder land portion in the tire meridian section. It passes through three points with the edge position near the shoulder land portion, and is depicted by an arc having a center on the inner side in the tire radial direction.

1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a development view showing a tread pattern of the pneumatic tire of FIG. 1. It is meridian sectional drawing which shows the outline shape of the tread part in the pneumatic tire of this invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. Note that the pneumatic tire of the present invention is designated in the mounting direction with respect to the vehicle. The side that is on the inner side of the vehicle (the side labeled “IN” in the drawing) when the vehicle is mounted is the “vehicle inner side”. The side that is on the outer side with respect to the vehicle at the time of mounting (the side indicated as “OUT” in the drawing) is referred to as “the vehicle outer side”.

  In FIG. 1, the symbol CL represents the tire equator. The pneumatic tire of the present invention includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, a pair of sidewall portions 2 that are disposed on both sides of the tread portion 1, and the tire radial direction of the sidewall portions 2 It is comprised from a pair of bead part 3 arrange | positioned inside. A carcass layer 4 (two layers in FIG. 1) is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back around the bead core 5 disposed in each bead portion 3 from the vehicle inner side to the outer side. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4. On the other hand, a plurality of layers (two layers in FIG. 1) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and these reinforcing cords are arranged so as to intersect each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. A plurality of (two layers in FIG. 1) belt reinforcing layers 8 are further provided on the outer peripheral side of the belt layer 7. The belt reinforcing layer 8 may include a layer that covers only the end of the belt layer 7 as illustrated in FIG. 1. The belt reinforcing layer 8 includes an organic fiber cord oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cord has an angle with respect to the tire circumferential direction set to, for example, 0 ° to 5 °.

  The present invention is applied to such a general pneumatic tire, but its cross-sectional structure is not limited to the basic structure described above.

  As shown in FIG. 2, four main grooves 11, 12, 13 and 14 extending in the tire circumferential direction are sequentially formed in the tread portion 1 from the vehicle inner side toward the vehicle outer side. The main grooves 11 to 14 define five rows of land portions 21, 22, 23, 24, and 25. More specifically, the tread portion 1 includes a pair of shoulder land portions 21 and 25 positioned on the outermost side in the tire width direction, and a center land portion 22 positioned between the pair of shoulder land portions 21 and 25. , 23, 24 are provided. In FIG. 2, Ein and Eout indicate grounding ends on the inside and outside of the vehicle, respectively, and the tread portion 1 forms a grounding region having a grounding width TCW. In the example of FIG. 2, among the four main grooves 11 to 14, the main groove 14 adjacent to the vehicle inner side of the shoulder land portion 25 has a groove width set smaller than the other main grooves 11 to 13. Yes.

  A plurality of lug grooves 31 extending in the tire width direction are arranged on the shoulder land portion 21 inside the vehicle at intervals in the tire circumferential direction. Each lug groove 31 is formed so that one end extends to the outer side in the tire width direction from the ground contact end Ein and the other end is not in communication with the main groove 11.

  A plurality of closing grooves 32 extending in the tire width direction are arranged at intervals in the tire circumferential direction in the center land portion 22 adjacent to the vehicle outer side of the shoulder land portion 21. Each closing groove 32 has one end communicating with the main groove 11 adjacent to the vehicle inner side of the center land portion 22, and the other end closed within the center land portion 22. The center land portion 22 is provided with a narrow groove 42 extending in the tire circumferential direction.

  A plurality of closing grooves 33 extending in the tire width direction are arranged at intervals in the tire circumferential direction in the center land portion 23 adjacent to the vehicle outer side of the center land portion 22. Each closing groove 33 has one end communicating with the main groove 12 adjacent to the inside of the center land portion 23 and the other end closed within the center land portion 23. The center land portion 23 is located on the tire equator CL, and the other end of each closing groove 33 does not exceed the tire equator CL and terminates on the inner side of the tire equator CL. The center land portion 23 is provided with a narrow groove 43 extending in the tire circumferential direction.

  A plurality of closing grooves 34 extending in the tire width direction are arranged at intervals in the tire circumferential direction in the center land portion 24 adjacent to the vehicle outer side of the center land portion 23. One end of each closing groove 34 communicates with the main groove 13 adjacent to the vehicle inner side of the center land portion 24, and the other end is closed in the center land portion 24. The center land portion 24 is provided with a narrow groove 44 extending in the tire circumferential direction.

  A plurality of closing grooves 35 extending in the tire width direction are arranged in the shoulder land portion 25 outside the vehicle at intervals in the tire circumferential direction. Each lug groove 35 is formed such that one end extends to the outside in the tire width direction from the ground contact end Eout and the other end communicates with the main groove 14.

  The narrow grooves 42 to 44 provided in all of the center land portions 22 to 24 have a width of 2% or more and 20% or less of the width of the land portions 22 to 24 provided with the respective narrow grooves 42 to 44. ing. Specifically, the groove width GW2 of the narrow groove 42 is 2% or more and 20% or less of the width RW2 of the center land portion 22, and the groove width GW3 of the narrow groove 43 is 2% or more of the width RW3 of the center land portion 23. The groove width GW4 of the narrow groove 44 is 2% or more and 20% or less of the width RW4 of the center land portion 24. The narrow grooves 42 to 43 are configured such that the groove width decreases from the vehicle inner side toward the vehicle outer side. Specifically, the groove width GW2 of the fine groove 42, the groove width GW3 of the fine groove 43, and the groove width GW4 of the fine groove 44 have a relationship of GW2> GW3> GW4. The narrow grooves 42 to 44 may intersect with or separate from the lug grooves 32 to 34 provided in the respective center land portions 22 to 24 (in the example of FIGS. 1 and 2, the narrow grooves 42 to 44 are formed in the center land portion 22. The narrow groove 42 intersects with the lug groove 32, but the narrow grooves 43 to 44 formed in the center land portions 23 to 24 are separated without intersecting with the lug grooves 33 to 34).

  The tread pattern described above is an example of the pneumatic tire according to the present invention. The tread portion 1 has at least three main grooves and at least four rows of land portions defined by the main grooves, and is adjacent to the tread pattern 1. If the above-mentioned narrow grooves are formed in all the land sections defined by two matching main grooves, and if the tread of each land section protrudes outward in the tire radial direction from the profile line as described later, It is not limited.

  FIG. 3 shows the contour shape of the tread portion 1 in the pneumatic tire of the present invention. However, FIG. 3 shows the outline shape exaggerated for easy understanding of the characteristics of the tread portion 1, and does not necessarily match the actual outline shape. In FIG. 3, the profile line TL of the tread portion 1 is composed of a center-side arc composed of a curvature radius Rc and both shoulder-side arcs composed of a curvature radius Rsh. Such a profile line TL of the tread portion 1 is specified based on the edge positions of the land portions 21 to 25 and the ground contact end position of the tread portion 1.

Specifically, the profile line TL in the shoulder land portion 21 includes a ground contact end position P ₁ of the shoulder land portion 21, an edge position P ₂ facing the main groove 11 of the shoulder land portion 21, and the shoulder land portion. The center land portion 22 adjacent to 21 passes through the edge position P ₃ on the side close to the shoulder land portion 21 and is depicted by an arc having a center on the inner side in the tire radial direction. The profile line TL in the center land portion 22 is on the side close to the center land portion 22 of the edge positions P ₃ and P ₄ on both sides of the center land portion 22 and the other center land portion 23 adjacent to the center land portion 22. as the edge position P _5, it is depicted by a circular arc having a center on the inner side in the tire radial direction. The profile line TL in the center land portion 23 is connected to the edge positions P ₅ and P ₆ on both sides of the center land portion 23 and the center land portion 22 of another center land portion 21 or 24 adjacent to the center land portion 23. It is depicted by an arc passing through the near edge position P ₄ or P ₇ and having a center in the tire radial direction. The profile line TL in the center land portion 24 is a side close to the center land portion 24 of the edge positions P ₇ and P ₈ on both sides of the center land portion 24 and the other center land portion 23 adjacent to the center land portion 24. as the edge position P _6, it is depicted by a circular arc having a center on the inner side in the tire radial direction. The profile line TL in the shoulder land portion 25 includes a ground contact end position P ₁₀ of the shoulder land portion 25, an edge position P ₉ facing the main groove 14 of the shoulder land portion 25, and a center adjacent to the shoulder land portion 25. It is depicted by an arc passing through the edge position P ₈ on the side of the land portion 24 close to the shoulder land portion 25 and having a center on the inner side in the tire radial direction.

  When the edge of each land portion is chamfered, the end point located on the outermost side in the tire radial direction of the chamfered portion is regarded as the edge position, and based on this edge position as described above. Determine the profile line.

  In the pneumatic tire, the treads of the center land portions 22 to 24 protrude outward in the tire radial direction from the profile line TL of the tread portion 1. Specifically, each of the center land portions 22 to 24 has a maximum protrusion position Pmax where the protrusion amount from the profile line TL is a maximum value, and the protrusion amount from the maximum protrusion position Pmax toward both sides in the tire width direction. Has a cross-sectional shape that gradually decreases. At this time, the amount of protrusion from the profile line TL of the tread surface of each center land portion 22 to 24 (the amount of protrusion T2 to T4 at the maximum protrusion position Pmax) is set in the range of 0.05 mm or more and 0.2 mm or less.

  By making the center land portions 22 to 24 protrude from the profile line TL of the tread portion 1 as described above, the ground contact shape of the center land portions 22 to 24 can be improved and the contact length can be extended. Thereby, the steering stability of the tire can be improved. However, if the center land portions 22 to 24 protrude from the profile line TL of the tread portion 1, a strong pressure is applied to the protruding portion when contacting the ground, so that there is a tendency that the contact pressure is excessive. In particular, in a vehicle intended for high-speed driving, the pneumatic tire is mounted so as to be a negative camber. Therefore, the ground pressure inside the vehicle is excessive among these center land portions 22 to 24, and excessive heat is generated during high-speed driving. Occurs, and rubber deterioration such as reversion occurs and failure is likely to occur (that is, high-speed durability deteriorates).

  Therefore, in this invention, while projecting from the profile line TL of the tread of each center land part 22-24 in the range of 0.05 mm or more and 0.2 mm or less, as above-mentioned in each center land part 22-24. Narrow grooves 42 to 44 are formed. That is, the rubber amount of each of the center land portions 22 to 24 can be reduced by providing the narrow grooves 42 to 44 while suppressing the increase in the contact pressure due to the land portion protruding by keeping the protrusion amount within an appropriate range. It is possible to reduce the excessive ground pressure caused by the center land portions 22 to 24 protruding. Further, since the narrow grooves 42 to 44 can be deformed inward in the groove width direction, excessive ground pressure can be suppressed from this point. As a result, it is possible to prevent deterioration in high-speed durability due to the protruding land portion. At this time, since the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are reduced from the inside of the vehicle toward the outside of the vehicle, the tendency of the ground pressure in the negative camber (the ground pressure on the inside of the vehicle is relatively high and The contact pressure excess of each center land part 22-24 can be suppressed appropriately according to the contact pressure being relatively low), and further improvement in high-speed durability can be expected. On the other hand, since the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are set according to the widths RW2 to RW4 of the center land portions 22 to 24 as described above, the land portions can be obtained by providing the narrow grooves 42 to 44. It is possible to prevent the rigidity from being significantly lowered, the effect by providing the narrow grooves 42 to 44 (improvement of high speed durability) and the effect by projecting the treads of the center land portions 22 to 24 from the profile line TL. (Improved handling stability) can be achieved in a balanced manner.

  At this time, if the protruding amounts T2 to T4 are smaller than 0.05 mm, the effect (improvement of steering stability) by protruding the treads of the center land portions 22 to 24 from the profile line TL cannot be sufficiently obtained. If the projecting amounts T2 to T4 are larger than 0.2 mm, the ground pressure of the center land portions 22 to 24 becomes very high, so that excessive ground pressure can be suppressed even if the narrow grooves 42 to 44 are provided. However, high-speed durability deteriorates. If the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are smaller than 2% of the widths RW2 to RW4 of the center land portions 22 to 24, the effect (suppression of excessive ground pressure) by providing the narrow grooves 42 to 44 is sufficient. Therefore, high-speed durability cannot be improved. If the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are larger than 20% of the widths RW2 to RW4 of the center land portions 22 to 24, the amount of rubber is greatly reduced by the narrow grooves 42 to 44, and the center land portion 22 The rigidity of ˜24 is lowered, and the steering stability is adversely affected. If the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are all equal or larger on the vehicle outer side than the vehicle inner side, the tendency of the ground pressure in the negative camber (the ground pressure on the inner side of the vehicle is relatively high and It becomes impossible to suppress excessive contact pressure according to the relatively low contact pressure, and it becomes difficult to sufficiently improve high-speed durability.

  Preferably, when the projecting amounts T2 to T4 of the tread surfaces of the center land portions 22 to 24 from the profile line TL are 0.05 mm or more and less than 0.5 mm, the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are the narrow grooves. It is 2% or more and less than 5% of the widths RW2 to RW4 of the center land portions 22 to 24 provided with 42 to 44, and the projecting amounts T2 to T4 of the tread of the land portions 22 to 24 from the profile line TL are 0.5 mm. When the width is less than 1.0 mm, the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are 5% or more and less than 10% of the widths RW2 to RW4 of the center land portions 22 to 24 provided with the narrow grooves 42 to 44. Yes, when the projection amounts T2 to T4 of the treads of the land portions 22 to 24 from the profile line TL are 1.0 mm or more and 2.0 mm or less, the groove widths GW2 to GW4 of the narrow grooves 42 to 44 are the narrow grooves 42 to 44, respectively. 44 May is 10% or more and 20% or less of the width RW2~RW4 of provided the center land portion 22 to 24. As a result, the land portions that are prone to excessive contact pressure due to the large protruding amounts T2 to T4 can suppress the excessive contact pressure by increasing the groove widths GW2 to GW4 of the narrow grooves 42 to 44, thereby achieving high-speed durability. It is advantageous to achieve a balance between improvement and maintenance of steering stability.

  In particular, in one tire, the protrusion amounts T1 to T5 of the land portions 21 to 25 may be different for each land portion. For example, the installation shape may be improved by changing the protrusion amounts T1 to T5. In such a case, as described above, the narrow grooves with respect to the widths RW2 to RW4 of the land portions 22 to 24 provided with the respective narrow grooves 42 to 44 according to the protrusion amounts T2 to T4 of the center land portions 22 to 24, respectively. By setting the ratio of the groove widths GW2 to GW4 of 42 to 44 within an appropriate range, it is possible to optimize the ground contact pressure and rigidity of the entire center land portions 22 to 24, improving high-speed durability and handling stability. It is possible to balance the maintenance of sex with a good balance.

  In the present invention, the “thin groove” is a groove whose groove width and depth are sufficiently smaller than the main grooves 11 to 14, and the groove width is set to 2 mm to 4 mm, for example, and the groove depth is set to 2 mm to 5 mm, for example. Is done. On the other hand, the main grooves 11 to 14 have a groove width of, for example, 10 mm to 20 mm, and a groove depth of, for example, 5 mm to 10 mm. An arbitrarily formed sipe (not shown) has a groove width of, for example, 1 mm to 1.5 mm. The groove depth is, for example, 2 mm to 6 mm.

  In particular, the groove depths d2 to d4 of the narrow grooves 42 to 44 of the present invention are preferably 20% to 50% of the groove depth of the main groove having the smallest groove depth among the main grooves 11 to 14. In the case of FIG. 3, since the groove depth D4 of the main groove 14 is the smallest among the main grooves 11 to 14, the groove depths d2 to d4 of the narrow grooves 42 to 44 are all 20% to 50% of the groove depth D4. % Is preferably set. By setting the groove depths d2 to d4 of the narrow grooves 42 to 44 in this way, it is possible to prevent the land portion rigidity from being significantly lowered and to maintain the steering stability appropriately. At this time, if the groove depths d2 to d4 of the narrow grooves 42 to 44 are smaller than 20% of the groove depth of the main groove having the smallest groove depth among the main grooves 11 to 14, the grounding by the narrow grooves 42 to 44 is performed. The effect of suppressing excessive pressure is limited, and the effect of improving high-speed durability cannot be obtained sufficiently. If the groove depths d2 to d4 of the narrow grooves 42 to 44 are smaller than 50% of the groove depth of the main groove having the smallest groove depth among the main grooves 11 to 14, the center land portion 22 is formed by the narrow grooves 42 to 44. Since the rigidity of ˜24 is greatly reduced, it becomes difficult to maintain high steering stability.

  The narrow grooves 42 to 44 can be provided at arbitrary positions of the center land portions 22 to 24, but preferably, the positions where the treads of the center land portions 22 to 24 protrude most from the profile line TL (each center land portion 22 It may be arranged at a maximum projecting position Pmax of ˜24. By arranging the narrow grooves 42 to 44 in this way, the protrusion amounts T2 to T4 are the maximum in each of the center land portions 22 to 24, so that the influence on the ground pressure is great. Since the effect is exhibited, excessive ground contact pressure can be accurately suppressed and high-speed durability can be improved. In the present invention, if the openings of the narrow grooves 42 to 44 are at the maximum projecting positions Pmax of the center land portions 22 to 24, the narrow grooves 42 to 44 are the profile treads of the center land portions 22 to 24. It is assumed that it is arranged at the position that protrudes most from

  The tire size is 325 / 30ZR21 (108Y), has the reinforcing structure illustrated in FIG. 1, and in the tire based on the tread pattern of FIG. 2, the protrusion amounts T2 to T4 of the center land portion, the presence or absence of narrow grooves, The ratio of the groove width of the narrow groove to the width of each center land portion GW2 / RW2, GW3 / RW3, GW4 / RW4, the groove depth of the narrow groove with respect to the groove depth of the main groove having the smallest groove depth among the main grooves 23 types of pneumatic tires of Conventional Example 1, Comparative Examples 1 to 3, and Examples 1 to 19 in which the ratios d2 / D4, d3 / D4, d4 / D4, and the positions of the narrow grooves were set as shown in Tables 1 and 2, respectively. Was made.

  In each example, the center land portion width RW2 is 40 mm, RW3 is 65 mm, and RW4 is 35 mm. In each example, the main groove outside the vehicle is the main groove having the smallest groove depth among the main grooves, and the groove depth D4 is 5.0 mm. Based on this D4, the groove depth ratio d2 / D4, d3 / D4, d4 / D4 was calculated. The groove depth of the main grooves other than the main groove on the outermost side of the vehicle is 8.0 mm.

  In the column of “Position of narrow groove” in Table 1, “Pmax” indicates the case where the narrow groove is arranged at the position where the tread surface protrudes most in each center land portion (maximum protrusion position), and the center in the width direction of each center land portion. The case of being arranged at the edge position of each center land portion is indicated as “Pe”.

  About these 23 types of pneumatic tires, the steering stability and high-speed durability were evaluated by the following evaluation methods, and the results are also shown in Tables 1 and 2.

Steering stability Each test tire is mounted on a wheel with a rim size of 21 × 11.5J (ETRTO standard rim) and mounted on a passenger car with a displacement of 4.8L, and dried under conditions of a front tire pressure of 230 kPa and a rear tire pressure of 240 kPa. A test course consisting of the road surface was run and a sensory evaluation was performed by a test driver. The evaluation results are shown as an index value in which Conventional Example 1 is 100. The larger the index value, the better the steering stability.

High-speed durability Each test tire is assembled to a wheel with a rim size of 21 × 11.5J (ETRTO standard rim) and mounted on a drum durability tester. Under conditions of air pressure 300 kPa, load 7.47 kN, and camber angle −2.2 ° Accelerate from 0 km / h to 230 km / h in 1 minute, then 230 km / h for 5 minutes, 280 km / h for 5 minutes, 290 km / h to 310 km / h in 10 km / h increments for 10 minutes, 320 km / h The speed at which the test machine detects the failure was measured by accelerating in steps of 10 km / h for 20 minutes until the failure occurred. For the evaluation results, measured values (real values of the speed at which the failure occurred) were used. It means that high speed durability is excellent, so that this index value is large.

  As is clear from Tables 1 and 2, all of Examples 1 to 19 improved the high-speed durability as compared with Conventional Example 1 while maintaining steering stability.

  On the other hand, in Comparative Example 1, since the groove width of the narrow groove is constant regardless of the width of the center land portion, the contact pressure of each land portion cannot be appropriately suppressed, and steering stability and high-speed durability are improved. It got worse. In Comparative Example 2, the groove width of the narrow groove is set according to the width of the center land portion, but since the groove width of the narrow groove is too small as a whole, the effect of improving the high speed durability was not sufficiently obtained. . In Comparative Example 3, the groove width of the narrow groove is set according to the width of the center land portion. However, since the groove width of the narrow groove is too large as a whole, the rigidity of the land portion is remarkably lowered and the steering stability is sufficiently improved. Could not be maintained.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt reinforcement layer 11-14 Main groove 21, 25 Shoulder land part 22-24 Center land part 31-35 Lug groove 42-44 Narrow groove CL Tire equator Ein, Eout Grounding end

Claims (4)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the inner side in the tire radial direction of the sidewall portions. The tread portion has at least three main grooves extending in the tire circumferential direction and at least four rows of land portions defined by the main grooves, and the tread portion has an edge position of the land portion in the meridian section and the land portion. In a pneumatic tire having a profile line in the tire width direction that is specified based on the contact end position of the tread portion, and in which a mounting direction with respect to the vehicle is designated,
In the meridian cross section, the tread of the land portion protrudes outward in the tire radial direction from the profile line, and the projecting amount of the tread surface of each land portion from the profile line is 0.05 mm or more and 0.2 mm or less, The land portion has at least one narrow groove extending in the tire circumferential direction, and the groove width of the narrow groove is 2% or more and 20% or less of the width of the land portion provided with the narrow groove. A pneumatic tire characterized in that the groove width of the narrow groove decreases from the inside of the vehicle, which is sometimes inside the vehicle, to the outside of the vehicle, which is outside the vehicle when the vehicle is mounted.   When the projecting amount of the tread of the land portion from the profile line is 0.05 mm or more and less than 0.5 mm, the groove width of the narrow groove is 2% or more and 5% of the width of the land portion provided with the narrow groove. When the protrusion amount of the tread surface of the land portion from the profile line is 0.5 mm or more and less than 1.0 mm, the groove width of the narrow groove is 5 of the width of the land portion provided with the narrow groove. The land portion in which the narrow groove is provided with a narrow groove width when the projecting amount of the tread of the land portion from the profile line is 1.0 mm or more and 2.0 mm or less. The pneumatic tire according to claim 1, wherein the pneumatic tire is 10% or more and 20% or less of the width of the tire.   The pneumatic tire according to claim 1 or 2, wherein a groove depth of the narrow groove is 20% to 50% of a groove depth of the main groove having the smallest groove depth among the main grooves.   The pneumatic tire according to any one of claims 1 to 3, wherein the narrow groove is disposed at a position where the tread surface of the land portion protrudes most from the profile line.

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