JP5251235B2 - Heavy duty pneumatic tire - Google Patents

Description

  The present invention relates to a heavy duty pneumatic tire that improves fuel efficiency.

  In heavy-duty pneumatic tires with ribs extending in the tire circumferential direction by providing circumferential main grooves along the tire circumferential direction in the tread part that forms the tread surface, rolling resistance is reduced and fuel efficiency is improved For this purpose, the rigidity of the tread portion may be increased. In order to increase the rigidity of the tread portion, it is conceivable to reduce the depth of the circumferential main groove or increase the rib width of the rib. However, when the depth of the circumferential main groove is reduced, there is a concern that wear resistance and wet resistance may be degraded. Further, when the rib width of the rib is increased, unless the tread development width is increased, the groove area is reduced and the wet resistance performance is lowered. On the other hand, if the tread deployment width is widened, the volume of the buttress portion increases, so that the mass increases and there is a concern that the rolling resistance will decrease.

  Conventionally, although the purpose is to suppress uneven wear, there is a heavy duty pneumatic tire in which the groove depth of the circumferential main groove and the rib width of the rib are defined with respect to the tread contact width (see, for example, Patent Document 1). . In this heavy duty pneumatic tire, the groove depth of the circumferential main groove is 4.5 [%] or more and 9.5 [%] or less (more preferably 5.0 [%] or more and 8.5%) of the tread contact width. [%] Or less). Further, the rib width of the rib is defined as 10 [%] to 18 [%] (more preferably 12 [%] to 15 [%]) of the tread contact width. Further, in this heavy-duty pneumatic tire, the relation between the center rib closest to the tire equator line, the shoulder rib of the shoulder portion, and the rib widths of the intermediate rib therebetween is defined. Specifically, the rib width of the center rib and the intermediate rib is formed substantially the same, and the rib width of the shoulder rib is formed relatively larger than that of the center rib and the intermediate rib. In the heavy-duty pneumatic tire described in Patent Document 1, in the embodiment, the groove depth of the circumferential main groove in the shoulder portion is 14 [mm], the groove width is 11 [mm], and the rib width of the center rib is 30 [mm], the rib width of the intermediate rib is 30 [mm], and the rib width of the shoulder rib is 43 [mm].

JP 2007-182097 A

  The present invention has been made in view of the above, and by appropriately defining the groove depth of the circumferential main groove and the rib width of the rib, the rolling resistance is reduced while maintaining the wet resistance performance, and the fuel efficiency is reduced. An object of the present invention is to provide a heavy duty pneumatic tire capable of improving the above.

  In order to achieve the above object, in the heavy-duty pneumatic tire according to the present invention, four or more circumferential main grooves extending in the tire circumferential direction and five or more ribs defined by the circumferential main grooves. In the heavy-duty pneumatic tire formed in the tread portion, the shoulder rib disposed on the outermost side in the tire width direction with respect to the groove depth Dg of the circumferential main groove on the outermost side in the tire width direction as a single tire Is set in the range of 2.60 ≦ Ws / Dg ≦ 3.20, and the rib width Wc of the center rib disposed closest to the tire equator line is 2.35 ≦ Wc / Dg ≦ 2. .70, and the rib width Wm of the intermediate rib disposed between the shoulder rib and the center rib is set in the range of 2.35 ≦ Wc / Dg ≦ 2.70, and The shoulder rib With respect to the width Ws, the rib width Wc of the center rib is set in a range of Wc ≦ Ws, the rib width Wm of the intermediate rib is set in a range of Wm ≦ Ws, and the groove depth The groove width Wg of the circumferential main groove is set in a range of 0.40 ≦ Wg / Dg ≦ 0.70 with respect to the length Dg.

  According to this heavy duty pneumatic tire, Ws / Dg, Wc / Dg, Wc / Dg, Wg / Dg are defined, and the groove width Wg of each circumferential main groove and the rib widths Ws, Wc, Wm of each rib are set. By optimizing the relationship between the rib widths Wc and Wm with respect to the rib width Ws, the rigidity of the tread portion can be increased while maintaining the wet resistance performance, so the rolling resistance is reduced and fuel efficiency is improved. it can.

  In the heavy-duty pneumatic tire according to the present invention, the angle θ of the groove wall on at least one side of the at least one circumferential main groove is 2 [degrees] ≦ the normal to the tread surface of the tread portion. It is characterized by being set in the range of θ.

  According to this heavy-duty pneumatic tire, the rigidity of the rib, that is, the rigidity of the tread portion can be increased, so that rolling resistance can be reduced and fuel efficiency can be further improved.

  Further, in the heavy duty pneumatic tire according to the present invention, the groove wall angle θ in the circumferential main groove at the outermost side in the tire width direction changes as it goes in the tire circumferential direction.

  According to this heavy-duty pneumatic tire, the rigidity of the rib, that is, the rigidity of the tread portion can be increased after securing the groove area without widening the groove width of the outer circumferential circumferential main groove in the tire width direction. The rolling resistance can be reduced to further improve fuel efficiency.

  Further, in the heavy-duty pneumatic tire according to the present invention, the reinforcing material in the outermost belt in the tire radial direction disposed in the tread portion, and the groove bottom of the circumferential main groove disposed closest to the tire equator line The thickness T of the rubber is between 3.5 [mm] ≦ T ≦ 5.5 [mm].

  According to this heavy-duty pneumatic tire, when the rubber thickness T is less than 3.5 [mm], there is a concern about the occurrence of cracks at the groove bottom. On the other hand, when the rubber thickness T exceeds 5.5 [mm], the distortion of the tread portion at the time of tire contact increases, the rib collapses, the rigidity of the tread portion is not increased, and the rolling resistance is reduced. Reduction effect is reduced. Therefore, the rubber thickness T between the reinforcing material and the bottom of the circumferential main groove disposed closest to the tire equator line is 3.5 [mm] ≦ T ≦ 5.5 [mm. ] Is preferably set in the range.

  The heavy duty pneumatic tire according to the present invention is characterized in that tan δ when the rubber of the tread portion is heated at 100 [° C.] is in a range of 0.07 ≦ tan δ ≦ 0.14.

  According to this heavy-duty pneumatic tire, when tan δ is less than 0.07, the productivity of the tire is deteriorated. On the other hand, when tan δ exceeds 0.14, the calorific value of the rubber in the tread portion increases and the rolling resistance of the tire increases. For this reason, it is preferable that tan δ at the time of 100 [° C.] heating of the rubber in the tread portion is in a range of 0.07 ≦ tan δ ≦ 0.14.

  In the heavy duty pneumatic tire according to the present invention, by appropriately defining the groove depth of the circumferential main groove and the rib width of the rib, it is possible to reduce rolling resistance and improve fuel efficiency while maintaining wet resistance.

  Embodiments of a heavy duty pneumatic tire according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  FIG. 1 is a meridional sectional view of a heavy duty pneumatic tire according to an embodiment of the present invention, and FIG. 2 is a sectional perspective view showing a circumferential main groove and a land portion of the heavy duty pneumatic tire shown in FIG. 3 is a sectional view showing a circumferential main groove of the heavy duty pneumatic tire shown in FIG. 1, FIG. 4 is a plan view showing a part of the tread portion of the heavy duty pneumatic tire shown in FIG. 1, and FIG. It is a graph which shows the result of the performance test of the pneumatic tire for heavy loads concerning embodiment of this invention.

  In the following description, the tire radial direction refers to a direction orthogonal to the rotation axis (not shown) of the heavy-duty pneumatic tire 1, and the tire radial direction inner side refers to the side toward the rotation axis in the tire radial direction, The outer side in the tire radial direction refers to the side away from the rotation axis in the tire radial direction. Further, the tire circumferential direction refers to a direction around the rotation axis as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction is the side toward the tire equatorial plane C in the tire width direction, and the outer side in the tire width direction is the tire equatorial plane C in the tire width direction. The side away from.

  Further, the heavy-duty pneumatic tire 1 described below is configured to be substantially symmetric with respect to the tire equatorial plane C. The tire equatorial plane C is a plane that is orthogonal to the rotation axis of the heavy duty pneumatic tire 1 and passes through the center of the tire width of the heavy duty pneumatic tire 1. The tire width is the width in the tire width direction between the portions located outside in the tire width direction, that is, the distance between the portions farthest from the tire equatorial plane C in the tire width direction. The tire equator line CL is a line that is on the tire equator plane C and extends along the circumferential direction of the heavy duty pneumatic tire 1. Since the heavy load pneumatic tire 1 described below is configured to be substantially symmetric about the tire equatorial plane C, the pneumatic tire 1 is in a plane passing through the rotation axis of the heavy load pneumatic tire 1. In the meridional sectional view (FIG. 1) when the tire is cut, only one side centering on the tire equatorial plane C is illustrated and only the one side is described, and description on the other side is omitted.

  As shown in FIG. 1, a heavy-duty pneumatic tire 1 according to the present embodiment includes a tread portion 2, shoulder portions 3 on both sides thereof, and a sidewall portion 4 and a bead portion 5 that are sequentially continuous from the shoulder portions 3. And have. The pneumatic tire 1 includes a carcass 6 and a belt layer 7.

  The tread portion 2 is exposed to the outside of the heavy load pneumatic tire 1, and the surface thereof becomes the contour of the heavy load pneumatic tire 1. A tread surface 21 is formed on the outer peripheral surface of the tread portion 2, that is, on the tread surface that contacts the road surface during traveling. The tread surface 21 includes four or more (four in the present embodiment) circumferential main grooves 22 formed to extend in the tire circumferential direction, and 5 defined by the circumferential main grooves 22. A rib pattern is formed by the ribs 23 that form more or more (5 in this embodiment) land portions.

  The shoulder portion 3 is a portion on both outer sides in the tire width direction of the tread portion 2. Further, the sidewall portion 4 is exposed at the outermost side in the tire width direction of the pneumatic tire 1. The bead unit 5 includes a bead core 51 and a bead filler 52. The bead core 51 is formed by winding a bead wire 51a, which is a steel wire, in a ring shape. The bead filler 52 is disposed in a space formed by folding the end of the carcass 6 outward in the tire width direction at the position of the bead core 51.

  The carcass 6 is configured such that each tire width direction end portion is folded with respect to the pair of bead portions 5 and is wound around in a toroidal shape in the tire circumferential direction to constitute a tire skeleton. The carcass 6 is a carcass cord made of organic fibers (such as nylon or polyester) or steel covered with rubber.

  The belt layer 7 is provided on the outer side in the tire radial direction than the carcass 6 in the tread portion 2. The belt layer 7 is a belt in which a cord (reinforcing material) such as organic fiber (nylon, polyester, etc.) or steel is covered with rubber, and a plurality of these belts are laminated. The belt layer 7 in the present embodiment is laminated in the order of the first belt 71, the second belt 72, the third belt 73, and the fourth belt 74 from the outer side in the tire radial direction of the carcass 6 toward the outer side in the tire radial direction. It has a four-layer structure.

  As shown in FIG. 2, the circumferential main grooves 22 and the ribs 23 provided in the tread portion 2 are applied to the heavy load pneumatic tire 1 as described below in the state of the tire alone without the rim assembly. It is prescribed.

  The rib width Ws of the opening portion of the shoulder rib 23s disposed on the outermost side in the tire width direction is 2.60 ≦ the groove depth Dg of the circumferential main groove 22s on the outermost side in the tire width direction (shoulder portion 3 side). The range is set to Ws / Dg ≦ 3.20. The rib width Wc of the opening of the center rib 23c disposed closest to the tire equator line CL is 2.35 ≦ Wc / Dg ≦ 2.70 with respect to the groove depth Dg of the circumferential main groove 22s. Set to range. Furthermore, the rib width Wm of the opening portion of the intermediate rib 23m disposed between the shoulder rib 23s and the center rib 23c is 2.35 ≦ Wc / Dg ≦ with respect to the groove depth Dg of the circumferential main groove 22s. The range is set to 2.70. Further, the rib width Wc of the center rib 23c is set in the range of Wc ≦ Ws with respect to the rib width Ws of the shoulder rib 23s. Furthermore, the rib width Wm of the intermediate rib 23m is set in the range of Wm ≦ Ws with respect to the rib width Ws of the shoulder rib 23s. Further, the groove width Wg of each circumferential main groove 22 is set in a range of 0.40 ≦ Wg / Dg ≦ 0.70 with respect to the groove depth Dg of the circumferential main groove 22s.

  Here, when Ws / Dg is less than 2.60, Wc / Dg is less than 2.35, Wc / Dg is less than 2.35, and Wg / Dg exceeds 0.70, each circumferential direction main Since the groove width Wg of the groove 22 is too wide and the rib widths Ws, Wc, and Wm of the ribs 23 are too narrow, the rigidity of the tread portion 2 is not increased, and the effect of reducing rolling resistance is reduced. In addition, when Ws / Dg exceeds 3.20, Wc / Dg exceeds 2.70, Wc / Dg exceeds 2.70, and Wg / Dg is less than 0.40, each circumferential direction main Since the groove width Wg of the groove 22 is too narrow and the rib widths Ws, Wc, Wm of the ribs 23 are too wide, the wet resistance performance is deteriorated. Furthermore, if Wc> Ws and Wm> Ws, the rib widths Wc and Wm of the center rib 23c and the intermediate rib 23m are too wide with respect to the shoulder rib 23s, so that the steering stability is deteriorated.

  That is, according to the heavy duty pneumatic tire 1 in which the circumferential main grooves 22 and the ribs 23 are defined as described above, the rigidity of the tread portion 2 is increased while maintaining the wet resistance performance, so that the rolling resistance is reduced. It becomes possible to improve fuel efficiency.

  The groove width Wg of each circumferential main groove 22 is preferably set in the range of 0.50 ≦ Wg / Dg ≦ 0.70 with respect to the groove depth Dg of the circumferential main groove 22s. It becomes possible to improve fuel efficiency.

  Further, in the heavy duty pneumatic tire 1 according to the present embodiment, as shown in FIG. 3, at least one side of at least one circumferential main groove 22 with respect to the normal h of the tread surface (tread surface) 21. The angle θ of the groove wall 22w is set in a range of 2 [degrees] ≦ θ, and preferably in a range of 2 [degrees] ≦ θ ≦ 15 [degrees].

  Specifically, as shown in FIG. 3A, the circumferential main groove 22 other than the circumferential main groove 22s on the outermost side in the tire width direction (shoulder portion 3 side), which is the tire equator in the present embodiment. In the circumferential main groove 22c disposed closest to the line CL, the angle θ of the groove walls 22w on both sides is in the range of 2 [degrees] ≦ θ, and preferably 2 [degrees] ≦ θ ≦ 15 [degrees]. ] Is set.

  According to such a configuration, by setting the angle θ of the groove wall 22w, the rigidity of the rib 23, that is, the rigidity of the tread portion 2 is increased, so that it is possible to reduce rolling resistance and further improve fuel efficiency. become.

  Further, as shown in FIG. 3B, the circumferential main groove 22s on the outermost side in the tire width direction (on the shoulder portion 3 side) has an angle θ of the groove wall 22w on one side of the meridian section of 0 [degree] = The angle θ of the groove wall 22w on the other side is set in a range of 2 [degrees] ≦ θ (preferably in a range of 2 [degrees] ≦ θ ≦ 15 [degrees]. The circumferential main groove 22s changes in a wavy or zigzag manner in such a manner that the angle θ of the groove wall 22w on one side and the angle θ of the groove wall 22w on the other side gradually reverse as they go in the tire circumferential direction. Is formed.

  According to this configuration, the angle θ of the groove wall 22w is set for the circumferential main groove 22s on the outermost side in the tire width direction (shoulder portion 3 side), and the angle θ changes as it goes in the tire circumferential direction. Since the groove area W is secured without increasing the groove width Wg of the circumferential main groove 22 (22s), the rigidity of the rib 23, that is, the rigidity of the tread portion 2 is increased, so that the rolling resistance is reduced and the fuel efficiency is reduced. It becomes possible to improve the property.

  Further, in the heavy-duty pneumatic tire 1 according to the present embodiment, as shown in FIG. 2, the reinforcing material in the fourth belt 74 on the outermost side in the tire radial direction of the belt layer 7 is disposed closest to the tire equator line. The rubber thickness T between the circumferential main groove 22c and the groove bottom 22b is set in a range of 3.5 [mm] ≦ T ≦ 5.5 [mm].

  When the rubber thickness T is less than 3.5 [mm], the generation of cracks at the groove bottom 22b is a concern. On the other hand, when the rubber thickness T exceeds 5.5 [mm], the distortion of the tread portion 2 at the time of tire contact increases, the rib 23 falls, and the rigidity of the tread portion 2 cannot be increased. The effect of reducing rolling resistance is reduced. For this reason, the rubber thickness T between the reinforcing member in the fourth belt 74 and the groove bottom 22b of the circumferential main groove 22c disposed closest to the tire equator line CL is 3.5 [mm]. It is preferable to set in the range of ≦ T ≦ 5.5 [mm].

  In the heavy-duty pneumatic tire 1 according to the present embodiment, tan δ when the rubber of the tread portion 2 is heated at 100 [° C.] is in the range of 0.07 ≦ tan δ ≦ 0.14.

  When tan δ is less than 0.07, tire productivity deteriorates. On the other hand, when tan δ exceeds 0.14, the calorific value of the rubber in the tread portion 2 increases and the rolling resistance of the tire increases. For this reason, it is preferable that tan δ when the rubber of the tread portion 2 is heated at 100 [° C.] is in the range of 0.07 ≦ tan δ ≦ 0.14.

  In the present embodiment, performance tests regarding rolling resistance (low fuel consumption), wet resistance, and steering stability were performed on a plurality of types of heavy-duty pneumatic tires having different conditions (see FIG. 5).

  In this performance test, a heavy-duty pneumatic tire having a tire size of 275 / 85R22.5 is assembled to a regular rim (for example, 22.5 × 7.50), filled with a specified internal pressure (for example, 900 [kPa]), and specified load (For example, 33.83 [kN]) was added. The regular rim here refers to an “applied rim” defined in JATMA, a “Design Rim” defined in TRA, or a “Measuring Rim” defined in ETRTO. The normal internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The normal load means “maximum load capacity” defined in JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined in TRA, or “LOAD CAPACITY” defined in ETRTO.

  As for the evaluation method, in rolling resistance, the rolling resistance is measured in increments of 20 [km / h] at a speed of 20 to 120 [km / h] with an indoor tester, and the measured value of the rolling resistance at each speed is measured. The average value of the rolling resistance coefficient divided by the load was obtained. Based on this average value, index evaluation using the conventional example as a reference (100) is performed. This evaluation is preferable as the numerical value increases. Further, in terms of wet resistance, a heavy-duty pneumatic tire was mounted on a vehicle having a total weight of 25 tons for a 2-D4 vehicle, and the braking distance on the wet road surface from an initial speed of 40 [km / h] was measured. Based on this measurement result, index evaluation is performed with the conventional example as a reference (100). This evaluation is preferable as the numerical value increases. In terms of steering stability, a heavy-duty pneumatic tire is mounted on a 2-D4 vehicle with a gross weight of 25 tons, and the feeling when traveling at a speed of 80 to 100 [km / h] is evaluated. 100) is evaluated. This evaluation is preferable as the numerical value increases.

  The conventional heavy load pneumatic tire has four main grooves in the circumferential direction, Ws / Dg, Wc / Dg, Wm / Dg, and Wg / Dg are not optimized, and Wc / Ws, Wm / Ws. Has been optimized. Further, the heavy duty pneumatic tires of Comparative Example 1 and Comparative Example 2 have four circumferential main grooves, and Ws / Dg, Wc / Dg, and Wm / Dg are not optimized, and Wc / Ws, Wm / Ws and Wg / Dg are optimized. Further, the heavy duty pneumatic tire of Comparative Example 3 has four circumferential main grooves, Wc / Ws and Wm / Ws are not optimized, and Ws / Dg, Wc / Dg, Wm / Dg, Wg / Dg is optimized. On the other hand, the heavy duty pneumatic tires of Examples 1 to 4 have four circumferential main grooves, Ws / Dg, Wc / Dg, Wm / Dg, Wc / Ws, Wm / Ws, Wg. / Dg is optimized.

  As shown in the test results of FIG. 5, it can be seen that in the heavy-duty pneumatic tires of Examples 1 to 4, the rolling resistance is reduced while maintaining wet resistance performance, and the steering stability is excellent.

1 is a meridional sectional view of a heavy duty pneumatic tire according to an embodiment of the present invention. Fig. 2 is a cross-sectional perspective view showing a circumferential main groove and a land portion of the heavy duty pneumatic tire shown in Fig. 1. It is sectional drawing showing the circumferential direction main groove of the heavy-duty pneumatic tire shown in FIG. FIG. 2 is a plan view showing a part of a tread portion of the heavy duty pneumatic tire shown in FIG. 1. It is a graph which shows the result of the performance test of the pneumatic tire for heavy loads concerning embodiment of this invention.

Explanation of symbols

1 Pneumatic tire for heavy load 2 Tread portion 22 (22s, 22c) Circumferential main groove 22w Groove wall 22b Groove bottom 23 rib 23s Shoulder rib 23c Center rib 23m Intermediate rib 3 Shoulder portion 6 Carcass 7 Belt layer 71 First belt 72 First Two belts 73 Third belt 74 Fourth belt h Normal line of tread surface Dg Depth of circumferential main groove on shoulder side Ws Rib width of shoulder rib Wc Rib width of center rib Wm Rib width of intermediate rib Wg Main in circumferential direction Groove Width θ Groove Wall Angle C Tire Equatorial Surface CL Tire Equatorial Line

Claims (5)

In a heavy duty pneumatic tire in which four or more circumferential main grooves extending in the tire circumferential direction and five or more ribs defined by the circumferential main grooves are formed in a tread portion,
Tire alone,
For the groove depth Dg of the circumferential main groove on the outermost side in the tire width direction,
The rib width Ws of the shoulder rib disposed on the outermost side in the tire width direction is set in a range of 2.60 ≦ Ws / Dg ≦ 3.20,
The rib width Wc of the center rib disposed closest to the tire equator line is set in a range of 2.35 ≦ Wc / Dg ≦ 2.70,
The rib width Wm of the intermediate rib disposed between the shoulder rib and the center rib is set in a range of 2.35 ≦ Wc / Dg ≦ 2.70,
The rib width Wc of the center rib is set in the range of Wc ≦ Ws with respect to the rib width Ws of the shoulder rib, and the rib width Wm of the intermediate rib is set in the range of Wm ≦ Ws. And
And the groove width Wg of the said circumferential direction main groove is set to the range of 0.40 <= Wg / Dg <= 0.70 with respect to the said groove depth Dg, The heavy duty pneumatic tire characterized by the above-mentioned.   The angle θ of the groove wall on at least one side of the at least one circumferential main groove is set in a range of 2 [degrees] ≦ θ with respect to the normal line of the tread surface of the tread portion. The heavy duty pneumatic tire according to claim 1.   3. The heavy duty pneumatic tire according to claim 1, wherein an angle θ of the groove wall in the circumferential main groove on the outermost side in the tire width direction changes as it goes in the tire circumferential direction.   The rubber thickness T between the reinforcing material in the outermost belt in the tire radial direction arranged in the tread portion and the groove bottom of the circumferential main groove arranged closest to the tire equator line is 3 The heavy-duty pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire is set in a range of .5 [mm]? T? 5.5 [mm].   5. The heavy load according to claim 1, wherein tan δ when the rubber of the tread portion is heated at 100 ° C. is in a range of 0.07 ≦ tan δ ≦ 0.14. Pneumatic tire.

Images