JP5609149B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire with improved uneven wear resistance and noise performance.

  Conventionally, a first main groove that extends in an annular shape while being bent in the tire circumferential direction is provided at the center portion of the tread surface, and two linearly extending in the tire circumferential direction on both sides in the tire width direction of the first main groove. The second main groove is provided, a first land portion is formed between the first main groove and each second main groove, and the first land portion extends in the tire width direction while inclining in the tire circumferential direction. There is a pneumatic tire in which first lug grooves are arranged at predetermined intervals in the tire circumferential direction. In this pneumatic tire, the groove width of the first main groove is 10% or less of the tire ground contact width, the bending width of the first main groove is in the range of 2 to 10 mm, and the second main groove is grounded from the tire equatorial plane. The first lug groove is disposed in a range of 20 to 35% of the width, and is curved and extended while being inclined with the inclination angle α to the tire circumferential direction being 35 to 50 °, while one end of the first lug groove is The corner portion of the acute angle portion of the rib that is communicated with the second main groove, the other end is separated from the first main groove, the first land portion is formed in the rib, and is sandwiched between the second main groove and the first lug groove Chamfered, one circumferential groove extending linearly in the tire circumferential direction is provided outside the tire width direction of each second main groove, and a second land portion is formed between the second main groove and the circumferential groove. And a second lug groove having one end communicating with the circumferential groove and the other end spaced apart from the second main groove at a predetermined interval in the tire circumferential direction. The second lug groove is curved and extended while the inclination angle β with respect to the tire circumferential direction is inclined within a range of 110 to 130% of the inclination angle α, while the inclination direction with respect to the tire circumferential direction is the first. The second lug groove extends in a circular arc shape with the acute angle portion side of the rib sandwiched between the circumferential groove and the second lug groove as a concave shape, opposite to the lug groove (see, for example, Patent Document 1).

  According to the pneumatic tire described in Patent Document 1, the groove width of the first main groove is set to 10% or less of the tire contact width, while the second main groove is set to 20% or more of the tire contact width from the tire equatorial plane. The tread rigidity of the center portion adjacent to the first main groove can be increased by arranging the first land portion in the rib without arranging the first lug groove in communication with the first main groove. In addition, driving stability on a dry road surface can be improved. In addition, by setting the bending width of the first main groove that is bent and extended to be 2 mm or more, it is possible to ensure traction by the edge effect of the first main groove.

  Further, according to the pneumatic tire described in Patent Document 1, while the first land portion is made into a rib, the inclination angle α of the first lug groove communicating with the second main groove is set to 35 ° or more, and the second main Since the corner portion of the acute angle portion of the rib sandwiched between the groove and the first lug groove is chamfered, uneven wear hardly occurs in the first land portion, and uneven wear resistance can be improved.

  Further, according to the pneumatic tire described in Patent Document 1, the second main groove extending linearly is disposed within a range of 35% or less of the tire ground contact width from the tire equator plane, while the first main groove is bent. The width of the first lug groove is made to be 10 mm or less, and the length of the first lug groove, which is shortened by the length not communicating with the first main groove, is extended in a curved shape so as to ensure a longer length than that extending linearly. Therefore, it becomes possible to ensure wet performance.

  Moreover, according to the pneumatic tire of patent document 1, by making a 1st lug groove incline, the edge sound of the 1st land part adjacent to a 1st lug groove reduces the striking sound, and noise is reduced. On the other hand, since the first land portion formed on the rib becomes difficult to vibrate, the noise performance can be improved.

Japanese Patent No. 4407765

  Thus, according to the pneumatic tire described in Patent Document 1 described above, driving stability on a dry road surface is improved, traction is ensured, uneven wear resistance is improved, wet performance is ensured, and noise is increased. It is possible to improve performance. However, in recent years, with the improvement in vehicle performance, further improvement in uneven wear resistance and noise performance is desired.

  This invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can improve uneven wear resistance and noise performance.

  In order to solve the above-described problems and achieve the object, the pneumatic tire of the present invention includes a center main groove extending along the tire circumferential direction at the position of the tire equatorial plane of the tread surface, and the center main groove. Each outer main groove extending along the tire circumferential direction on both outer sides in the tire width direction, a leading end communicating with the outer main groove and a leading end not communicating with the center main groove, and with respect to the tire circumferential direction A plurality of lug grooves that are formed to be inclined and arranged in the tire circumferential direction, and a sipe that is formed to be inclined with respect to the tire circumferential direction while both ends are not connected to the lug groove between the lug grooves, The lug groove is provided with a bottom upper portion formed with a shallow groove bottom at a tip portion, and the sipe has a longitudinal direction as a tire circumferential direction, and a longitudinal center is the bottom upper portion. In the tire width direction area It is characterized in that is.

  According to this pneumatic tire, noise can be reduced by the bottom upper portion of the lug groove. In addition, the sipe with the center in the longitudinal direction placed between the lug grooves provided with the bottom upper part distributes the stress applied to the land part provided with the lug grooves, thereby suppressing initial uneven wear when the tire is new. can do.

  In the pneumatic tire of the present invention, the end of the sipe is disposed in a range of 2 [mm] to 5 [mm] from the opening edge of the tread surface of the lug groove. .

  If the distance between the sipe and the lug groove is less than 2 [mm], the sipe and the lug groove may be broken. On the other hand, when the distance between the sipe and the lug groove exceeds 5 [mm], it is difficult to obtain the effect of suppressing uneven wear because the dispersion of stress is small. That is, according to this pneumatic tire, the effect of noise performance and uneven wear resistance can be remarkably obtained by defining the arrangement of sipes with respect to the lug grooves.

  In the pneumatic tire of the present invention, the lug groove has a chamfered portion in which a part of an opening edge on the acute angle portion side formed between the lug groove and the outer main groove is chamfered. And

  According to this pneumatic tire, since the chamfered portion suppresses an increase in the lug groove due to the chipping of the opening edge, it is possible to improve uneven wear resistance and noise performance.

  In the pneumatic tire of the present invention, the lug groove is inclined at 20 [°] or more and 60 [°] or less with respect to the tire circumferential direction as it approaches the tire equatorial plane, and is a groove from the starting end toward the leading end. The width is gradually narrowed.

  According to this pneumatic tire, it is possible to reduce the sound of hitting the road surface by the edge of the land portion provided with the lug groove, and to reduce the noise.

  Further, in the pneumatic tire of the present invention, the center main groove is formed to be bent or curved at a constant cycle, and the inflection point is arranged in a region in the tire circumferential direction of the sipe. To do.

  According to this pneumatic tire, the stress generated on the tread surface is released from the lug groove to the sipe side, so that the stress can be further dispersed.

  The pneumatic tire according to the present invention can improve uneven wear resistance and noise performance.

FIG. 1 is a plan view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged plan view of the pneumatic tire shown in FIG. 3 is a cross-sectional view taken along line AA in FIG. FIG. 4 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention.

  Embodiments of 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.

  In the following description, the tire radial direction refers to a direction orthogonal to the rotation axis (not shown) of the pneumatic tire 1, and the tire radial direction inner side refers to the side toward the rotation axis in the tire radial direction, the tire radial direction outer side. The term “side away from the rotation axis” in the tire radial direction. The tire circumferential direction is a circumferential direction with 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 means the side toward the tire equatorial plane C in the tire width direction, and the outer side in the tire width direction means the tire equatorial plane in the tire width direction. The side away from C. The tire equatorial plane C is a plane that is orthogonal to the rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1.

  The pneumatic tire 1 of the present embodiment is particularly suitable as a tire for light trucks. As shown in FIG. 1, the pneumatic tire 1 has a tread portion 2. The tread portion 2 is made of a rubber material, and is exposed at the outermost side in the tire radial direction of the pneumatic tire 1, and the surface (hereinafter referred to as a tread surface) 21 becomes the contour of the pneumatic tire 1.

  The tread surface 21 of the tread portion 2 is provided with a center main groove 31 extending along the tire circumferential direction at the position of the tire equatorial plane C. The tread surface 21 is provided with outer main grooves 32 extending along the tire circumferential direction on both outer sides of the center main groove 31 in the tire width direction. Further, the tread surface 21 is provided with circumferential grooves 33 extending along the tire circumferential direction on both outermost sides in the tire width direction. A center land portion 41 closest to the tire equatorial plane C is formed between the center main groove 31 and the outer main groove 32. An intermediate land portion 42 that is second closest to the tire equator plane C is formed between the outer main groove 32 and the circumferential groove 33. Further, an outermost shoulder land portion 43 in the tire width direction farthest from the tire equatorial plane C is formed on the outer side in the tire width direction of the circumferential groove 33.

  The center main groove 31 may be formed linearly in the tire circumferential direction, but in the present embodiment, the center main groove 31 is provided to extend in the tire circumferential direction while being bent or curved at a constant period. The bending (curving) width W1 of the center main groove 31 is set in the range of 2 [mm] or more and 10 [mm] or less from the center of the amplitude (in the present embodiment, coincides with the tire equatorial plane C). When the bending width W1 is less than 2 [mm], drainage is good, but it is difficult to ensure traction by the edge effect of the center main groove 31. On the other hand, when the bending width W1 exceeds 10 [mm], the traction property can be ensured, but the bending becomes too large and the drainage property is deteriorated. Preferably, the bending width W1 is not less than 4 [mm] and not more than 8 [mm].

  Further, the center main groove 31 has a groove width G1 that is 10% or less of the tire ground contact width TW. If the groove width G1 of the center main groove 31 exceeds 10% of the tire ground contact width TW, the tread rigidity in the vicinity of the tire equatorial plane C decreases, so the effect of improving the steering stability when driving on a dry road surface decreases. To do. Preferably, the groove width G1 is 8% or less of the tire ground contact width TW. The lower limit of the groove width G1 is preferably 3% or more of the tire ground contact width TW from the viewpoint of drainage.

  The outer main groove 32 is formed linearly in the tire circumferential direction, and the groove center is arranged in the range of 20% to 35% of the tire ground contact width TW from the tire equatorial plane C toward the outer side in the tire width direction. Has been. When the outer main groove 32 is disposed on the inner side in the tire width direction from the position of 20 [%] of the tire ground contact width TW, the rigidity of the center land portion 41 is reduced, and the steering stability improvement effect when driving on the dry road surface is reduced. Decreases. On the other hand, when the outer main groove 32 is disposed on the outer side in the tire width direction from the position of 35 [%] of the tire ground contact width TW, drainage performance is deteriorated.

  In the circumferential groove 33, the groove center is disposed in a range of 30% to 50% of the tire ground contact width TW from the tire equatorial plane C toward the outer side in the tire width direction. As a result, the contact pressure on the shoulder side can be reduced and the contact pressure on the tread surface 21 can be made uniform, so that uneven wear due to the contact pressure difference between the center side and the shoulder side is suppressed, and noise during wear is reduced. And contributes to suppression of passing sound. Preferably, in the circumferential groove 33, the center of the groove is arranged in a range of 35% to 45% of the tire ground contact width TW from the tire equatorial plane C toward the outer side in the tire width direction.

  Further, the groove width G <b> 3 of the circumferential groove 33 is formed in a range of 45 [%] to 65 [%] of the groove width G <b> 2 of the outer main groove 32. If the groove width G3 of the circumferential groove 33 is less than 45% of the groove width G2 of the outer main groove 32, it is difficult to effectively reduce the ground contact pressure on the shoulder side. On the other hand, when the groove width G3 of the circumferential groove 33 exceeds 65 [%] of the groove width G2 of the outer main groove 32, the ground contact pressure on the shoulder side is excessively reduced, and therefore center wear is likely to occur. Preferably, the groove width G3 of the circumferential groove 33 may be formed in a range of 50% to 60% of the groove width G2 of the outer main groove 32.

  Here, the tire ground contact width TW is the tread of the tread portion 2 of the pneumatic tire 1 when the pneumatic tire 1 is assembled on a regular rim and filled with a regular internal pressure and 70% of the regular load is applied. This is the maximum width in the tire width direction of a region where the surface 21 contacts the road surface (hereinafter referred to as a contact region). Further, both outermost ends in the tire width direction of the contact area are referred to as tire contact ends.

  The regular rim is “standard rim” defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO. The normal internal pressure is “maximum air pressure” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The normal load is “maximum load capacity” defined by JATMA, a maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO.

  The center land portion 41 has a lug groove 51 formed therein. The lug groove 51 has a leading end communicating with the outer main groove 32 and a leading end not communicating with the center main groove 31. Thereby, the center land part 41 is formed in a rib shape continuous in the tire circumferential direction. As shown in FIG. 2, the lug grooves 51 are formed to be inclined with respect to the tire circumferential direction and are arranged in the tire circumferential direction. Further, the lug groove 51 has the same inclination direction with respect to the tire circumferential direction in each center land portion 41, and each center land portion 41 also has the same inclination direction with respect to the tire circumferential direction. They are arranged symmetrically with respect to each other.

  As shown in FIGS. 2 and 3, the lug groove 51 is provided with a bottom upper portion 51 a having a shallow groove bottom at the tip. The bottom upper portion 51a is provided with a tire width direction dimension W3 from the leading end of the lug groove 51 to the starting end with respect to the tire width direction dimension W2 of the lug groove 51 in a range of 20 [%] to 50 [%]. Yes. Further, the bottom upper portion 51a has a height H2 raised from the deepest groove depth H1 of the lug groove 51 in a range of 40 [%] to 65 [%]. In the present embodiment, the bottom upper portion 51a is formed in one step from the deepest groove bottom of the lug groove 51 as shown in FIG. 3, but it may be formed in a plurality of steps and gradually raised to the bottom. It may be formed in the form.

  The lug groove 51 is curved and formed so that the inclination angle with respect to the tire circumferential direction changes in a range of 20 [°] or more and 60 [°] or less as it approaches the tire equatorial plane C from the starting end to the tip. Yes. This inclination angle is an angle with respect to the tire circumferential direction of a tangent line of the center line 51b of the groove width in the curved lug groove 51. The center line 51b is the AA line in FIG. 2 representing the cross section of FIG.

  Further, the lug groove 51 is formed such that the inclination angle α1 with respect to the tire circumferential direction is 35 [°] or more on the acute angle side. If the inclination angle α1 is less than 35 [°], uneven wear tends to occur at the corner portion of the acute angle portion 41a of the center land portion 41 sandwiched between the outer main groove 32 and the lug groove 51. The upper limit value of the inclination angle α1 is preferably set to 50 ° or less in relation to a shoulder side lug groove 52 described later from the viewpoint of noise performance. Note that the inclination angle α1 of the lug groove 51 that is curved and extends is, as shown in FIG. 2, a straight line connecting the starting side point 51x and the tip side point 51y of the center line 51b of the lug groove 51 with respect to the tire circumferential direction. Is an angle. The lug groove 51 is formed so that the groove width is gradually narrowed from the starting end toward the tip.

  Further, the lug groove 51 is formed with a chamfered portion 51 c having a chamfered opening edge on the acute angle portion 41 a side of the center land portion 41 sandwiched between the outer main groove 32 and the lug groove 51 on the tread surface 21. The chamfered portion 51c is preferably provided on all of the opening edges on the acute angle portion 41a side of the center land portion 41, but at least a portion communicating with the outer main groove 32 or a portion communicating with the outer main groove 32. It may be provided in the vicinity.

  Furthermore, the sipe 61 is formed between the lug grooves 51 in the center land portion 41. The sipe 61 is formed in a straight line, is inclined with respect to the tire circumferential direction, and is provided with the longitudinal direction as the tire circumferential direction. In the sipe 61, the longitudinal center 61a is in the tire width direction region where the bottom upper portion 51a of the lug groove 51 is provided, and the tire width direction from the tip of the lug groove 51 to the starting end in the bottom upper portion 51a. It arrange | positions in the dimension W3.

  Further, the end of the sipe 61 is disposed in a range of 2 [mm] or more and 5 [mm] or less from the opening edge of the tread surface 21 of the lug groove 51.

  Further, the relationship between the sipe 61 and the center main groove 31 is such that the inflection point P of the center main groove 31 bent or curved at a constant period in the tire width direction is a tire circumferential dimension of the sipe 61 in the tire circumferential direction region. It is provided to be within the range of L.

  Such a sipe 61 is not limited to one location between the lug grooves 51, and a plurality of sipes 61 may be provided. In the case where a plurality of sipes 61 are provided, it is only necessary that at least one sipe 61 is disposed in the tire width direction region (the tire width direction dimension W3) in the bottom upper portion 51a of the lug groove 51.

  As shown in FIG. 1, the intermediate land portion 42 is provided with a shoulder side lug groove 52. The shoulder side lug groove 52 has a leading end communicating with the circumferential groove 33 and a leading end not communicating with the outer main groove 32. Thus, the intermediate land portion 42 is formed in a rib shape continuous in the tire circumferential direction. The shoulder side lug grooves 52 are formed to be inclined with respect to the tire circumferential direction, and a plurality of the shoulder side lug grooves 52 are arranged in the tire circumferential direction. Further, the shoulder side lug groove 52 has the same inclination direction with respect to the tire circumferential direction in each intermediate land portion 42, and each intermediate land portion 42 also has the same inclination direction with respect to the tire circumferential direction, so that the tire equatorial plane They are arranged symmetrically with respect to C.

  The shoulder-side lug groove 52 is provided with a bottom upper portion 52a having a shallow groove bottom at the tip. The bottom upper portion 52a may be formed in one step from the deepest groove bottom of the shoulder side lug groove 52, but may be formed in a plurality of steps, or may be formed in a gradually raised form. Good.

  In addition, the shoulder side lug groove 52 is inclined in the range of 110 [%] to 130 [%] of the inclination angle α1 of the lug groove 51 on the acute angle side with respect to the tire circumferential direction, and to the tire circumferential direction. It is curved and extended while the inclination direction is opposite to the lug groove 51.

  In this way, by shifting the inclination angle α3 of the shoulder side lug groove 52 with respect to the inclination angle α1 of the lug groove 51, the noise peak frequency band by the lug groove 51 and the noise peak frequency band by the shoulder side lug groove 52 are changed. Shifting prevents the pattern noise from being amplified due to both lug grooves 51 and 52. If the inclination angle α3 is less than 110 [%] of the inclination angle α1, the above-described effect cannot be obtained, and the inclination angle α3 is biased toward the acute angle portion 42a of the intermediate land portion 42 sandwiched between the circumferential groove 33 and the shoulder side lug groove 52. Wear tends to occur. On the other hand, when the inclination angle α3 exceeds 130 [%] of the inclination angle α1, the effect of reducing the hitting sound of the edge of the shoulder side lug groove 52 hitting the road surface is reduced. As shown in FIG. 1, the inclination angle α3 of the shoulder side lug groove 52 extending in a curved manner is a straight line connecting the starting side point 52x and the leading end side point 52y of the center line 52b of the shoulder side lug groove 52. It is an angle with respect to the tire circumferential direction.

  As shown in FIG. 1, the shoulder land portion 43 is provided with a shoulder side sipe 62 and a shoulder side sipe 63. The shoulder side sipe 62 communicates with the circumferential groove 33 and is formed to extend linearly from the circumferential groove 33 while being inclined in the tire circumferential direction on the outer side in the tire width direction. Further, two shoulder-side sipes 63 are arranged between the shoulder-side sipes 62, and are formed so as to extend linearly while inclining in the tire circumferential direction without communicating with the circumferential groove 33.

  In the pneumatic tire 1 configured as described above, the groove width G1 of the center main groove 31 is set to 10% or less of the tire ground contact width TW, and the outer main groove 32 extends from the tire equatorial plane C to the tire ground contact width TW. The tread rigidity at the center portion of the tread portion 2 can be increased by disposing the lug groove 51 in a range of 20 [%] or more, and forming the center land portion 41 in a rib shape without communicating with the center main groove 31. Therefore, it is possible to improve the handling stability on the dry road surface. Further, by setting the bending width W1 of the center main groove 31 to 2 [mm] or more, it becomes possible to ensure traction by the edge effect of the center main groove 31.

  Further, the center land portion 41 is formed in a rib shape, the inclination angle α1 of the lug groove 51 communicating with the outer main groove 32 is set to 35 ° or more, and the center land portion sandwiched between the outer main groove 32 and the lug groove 51. Since the acute angle portion 41a of 41 is chamfered, uneven wear hardly occurs in the rib-shaped center land portion 41, and the uneven wear can be improved.

  Further, the outer main groove 32 extending linearly is disposed in a range of 35 [%] or less of the tire ground contact width TW from the tire equatorial plane C, and the bending width W1 of the center main groove 31 is set to 10 [mm] or less. Furthermore, the lug groove 51 whose length is shortened by the amount of non-communication is extended in the center main groove 31 in a curved shape so as to ensure a longer length than that extending linearly, ensuring wet performance. It becomes possible to do.

  In addition, by inclining the lug groove 51, it is possible to reduce the hitting sound of the edge of the center land portion 41 formed by the lug groove 51 hitting the road surface and to reduce the noise. In addition, since the center land portion 41 is less likely to vibrate in the tire width direction, noise performance can be improved.

  The tire width direction dimension W9 from the tip of the lug groove 51 to the center main groove 31 is preferably in the range of 105% to 150% with respect to the groove width G1 of the center main groove 31. If the dimension W9 is less than 105 [%] of the groove width G1, the rigidity of the center land portion 41 between the tip of the lug groove 51 and the center main groove 31 is locally reduced, and therefore uneven wear occurs. It becomes easy. On the other hand, when the dimension W9 exceeds 150 [%] of the groove width G1, the drainage performance is deteriorated. Preferably, the dimension W9 is 110 [%] or more and 140 [%] or less.

  In particular, in the pneumatic tire 1 of the present embodiment, the lug groove 51 is provided with a bottom upper portion 51a having a shallow groove bottom at the tip, and the sipe 61 provided between the lug grooves 51 has a longitudinal direction. Is the tire circumferential direction, and the center 61a in the longitudinal direction is disposed in the tire width direction region (tire width direction dimension W3) of the bottom upper portion 51a.

  According to the pneumatic tire 1, noise can be reduced by the bottom upper portion 51 a of the lug groove 51. Moreover, since the stress applied to the center land portion 41 is dispersed by the sipe 61 in which the longitudinal center 61a is disposed between the lug grooves 51 provided with the bottom upper portion 51a, the initial uneven wear when the tire is new is suppressed. It becomes possible to do. Here, if the inclination angle α2 of the sipe 61 with respect to the tire circumferential direction is too large, it causes uneven wear. Therefore, the inclination angle α2 is preferably in the range of 10 ° to 30 ° on the acute angle side. . Furthermore, in order to suppress uneven wear, the sipe 61 preferably has a groove depth of 10% or more with respect to the deepest groove depth H1 of the lug groove 51.

  Further, in the pneumatic tire 1 of the present embodiment, the end of the sipe 61 is disposed in the range of 2 [mm] to 5 [mm] from the opening edge of the tread surface 21 of the lug groove 51.

  If the distance between the sipe 61 and the lug groove 51 is less than 2 [mm], the sipe 61 and the lug groove 51 may be broken. On the other hand, when the distance between the sipe 61 and the lug groove 51 exceeds 5 [mm], it is difficult to obtain the effect of suppressing uneven wear because the dispersion of stress is small. In order to obtain a remarkable effect of suppressing uneven wear, the sipe 61 has a tire width direction dimension W4 from an end portion on the side close to the tire equatorial plane C to an edge on the outer main groove 32 side of the center land portion 41. The groove 51 is preferably in the range of 70% to 90% with respect to the tire width direction dimension W2. Further, in the sipe 61, the tire width direction dimension W5 from the end on the side far from the tire equatorial plane C to the edge on the outer main groove 32 side of the center land portion 41 is the outer side in the tire width direction of the bottom upper portion 51a in the lug groove 51. It is preferably in the range of 70% to 110% with respect to the tire width direction dimension W6 from the end to the outer main groove 32.

  In the pneumatic tire 1 of the present embodiment, the lug groove 51 is chamfered by chamfering a part of the opening edge on the acute angle portion 41a side of the center land portion 41 formed between the outer main groove 32 and the lug groove 51. It has a part 51c.

  According to the pneumatic tire 1, since the chamfered portion 51c minimizes the increase in the lug groove 51 due to the opening edge chipping, it is possible to improve uneven wear resistance and noise performance. Here, in order to obtain the above-described effect remarkably, it is preferable that the chamfered portion 51c has a dimension between the chamfered edges of 1.0 [mm] or more and 1.5 [mm] or less.

  In the pneumatic tire 1 of the present embodiment, the lug groove 51 is inclined at 20 [°] or more and 60 [°] or less with respect to the tire circumferential direction as it approaches the tire equatorial plane C, and from the leading end to the tip. The groove width is formed so as to be gradually narrower toward.

  According to the pneumatic tire 1, it is possible to reduce the noise caused by the edge of the center land portion 41 formed by the lug groove 51 hitting the road surface and to reduce the noise. Here, in order to obtain the above-mentioned effect remarkably, the lug groove 51 is tapered so that the narrowest groove width T2 on the leading end side is 60% or more and 75% or less with respect to the widest groove width T1 on the starting end side. It is preferable. The widest groove width T1 on the starting end side is an opening width that opens to the outer main groove 32 side. The narrowest groove width T2 on the tip side is an opening width that opens to the tread surface 21 in a portion excluding an arc formed at the tip of the lug groove 51 in an arc shape.

  Further, in the pneumatic tire 1 of the present embodiment, the center main groove 31 is formed to be bent or curved at a constant cycle, and the inflection point P is an area in the tire circumferential direction of the sipe 61 (tire circumferential dimension L). ).

  According to the pneumatic tire 1, the stress generated on the tread surface 21 is released from the lug groove 51 to the sipe 61 side, so that the stress can be further dispersed. Here, in order to obtain the above effect remarkably, the relationship between the sipe 61 and the center main groove 31 is that the amplitude W7 of the center main groove 31 is such that the tire width direction dimension W8 between the tire equatorial plane C and the center 61a of the sipe 61 is as follows. It is preferable that it is the range of 10 [%] or more and 20 [%] or less. Furthermore, the relationship between the sipe 61 and the center main groove 31 is that the groove width G1 of the center main groove 31 is 20% or more with respect to the tire width direction dimension W8 between the tire equatorial plane C and the center 61a of the sipe 61. The range is preferably 40% or less.

  In this example, performance tests on pattern noise (noise performance) and uneven wear resistance were performed on a plurality of types of pneumatic tires with different conditions (see FIG. 4).

  In this performance test, a pneumatic tire with a tire size of 165R13 is assembled to a rim of 13 × 5J and mounted on the front and rear of a test vehicle (commercial vehicle with a maximum load capacity of 400 [kg]), and the front is 220 [kPa]. The air pressure of 280 [kPa] was filled in the rear.

  In the pattern noise evaluation method, the in-vehicle noise when the test vehicle is driven at 40 [km / h] on the test vehicle is evaluated based on the conventional example by sensory evaluation. In this case, the index is shown with an index of 100, and the higher the index, the more the noise is reduced and the noise performance is higher.

  In the evaluation method of uneven wear resistance, the tire appearance is evaluated based on a conventional example by visual evaluation after running the public road for 15000 [km] on the test vehicle. In this case, the index is represented by an index with the reference being 100, and the higher the index, the more the uneven wear is suppressed and the uneven wear resistance is higher.

  In the conventional pneumatic tire, sipes are provided between the lug grooves, but the bottom upper portion is not provided in the lug grooves. In contrast, in Examples 1 to 8, sipes are provided between the lug grooves, and the bottom upper portion is provided in the lug grooves. In Examples 2 and 3, the distance from the lug groove is further defined in the sipe arrangement. In Examples 4 and 5, a chamfered portion is further provided. In Examples 6 and 7, the inclination angle of the lug groove is further defined. In the eighth embodiment, the center main groove is further bent or curved.

  As shown in the test results of FIG. 4, it can be seen that in the pneumatic tires of Examples 1 to 8, pattern noise (noise performance) and uneven wear resistance are improved.

  As described above, the pneumatic tire according to the present invention is suitable for improving uneven wear resistance and noise performance.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 21 Tread surface 31 Center main groove 32 Outer main groove 33 Circumferential groove 41 Center land part 41a Sharp corner part 42 Intermediate land part 42a Sharp corner part 43 Shoulder land part 51 Lug groove 51a Bottom upper part 51b Center line 51c surface 51x Starting side point 51y Tip side point 61 Sipe 61a Center W1 Center main groove bending width C Tire equatorial plane G1 Center main groove groove width G2 Outer main groove groove width G3 Circumferential groove width L Sipe tire Circumferential dimension P Inflection point of center main groove T1 Groove width on start side of lug groove T2 Groove width on tip side of lug groove TW Tire contact width W1 Bending width of center main groove W2 Tire width direction dimension of lug groove W3 Tire width dimension at the top of the bottom W4 Size of tire width direction from the end near the tire equatorial plane of Sipe to the outer main groove W5 Tire equatorial plane of Sipe Tire width direction dimension from the end far from the outer main groove to the outer main groove W6 Tire width direction dimension from the outer end of the tire width direction at the bottom to the opening to the outer main groove W7 Center main groove amplitude W8 Tire equatorial plane and sipe Tire width direction dimension with the center of tire W9 Tire width direction dimension from tip of lug groove to center main groove α1 Inclination angle of lug groove α2 Inclination angle of sipe

Claims (4)

A center main groove extending along the tire circumferential direction at the position of the tire equatorial plane of the tread surface, each outer main groove extending along the tire circumferential direction on both outer sides in the tire width direction of the center main groove, and Between the lug grooves and the lug grooves formed in an inclined manner with respect to the tire circumferential direction and having a plurality of arrangements in the tire circumferential direction, with a leading end communicating with the outer main groove and a tip not communicating with the center main groove In a pneumatic tire provided with both ends of the sipe and the sipe formed to be inclined with respect to the tire circumferential direction.
The lug groove is provided with a bottom upper portion formed with a shallow groove bottom at the tip portion, and the groove width is gradually narrowed from the starting end toward the tip,
The sipe has a tire circumferential direction in the longitudinal direction, a center in the longitudinal direction is arranged in a region in the tire width direction of the bottom upper portion, and an end thereof is 2 mm or more from an opening edge of the tread surface of the lug groove A pneumatic tire characterized by being arranged in a range of 5 mm or less.   2. The pneumatic device according to claim 1, wherein the lug groove has a chamfered portion formed by chamfering a part of an opening edge on an acute angle portion side formed between the lug groove and the outer main groove. tire. 3. The pneumatic tire according to claim 1, wherein the lug groove is inclined at 20 [°] or more and 60 [°] or less with respect to the tire circumferential direction as approaching the tire equatorial plane.   The center main groove is formed by being bent or curved at a constant period, and an inflection point thereof is disposed in a region in the tire circumferential direction of the sipe. Pneumatic tire described in one.

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