JP5592783B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that improves steering stability performance and noise performance in a well-balanced manner while maintaining wet performance.

  Conventionally, it is known to increase the rigidity of the land portion by increasing the land ratio of the tread portion as much as possible in order to improve the steering stability performance on the dry road surface. In particular, in the crown region of the tread portion, the contact pressure is likely to be larger than that in the shoulder region. Therefore, it is effective to reduce the groove volume in the crown region and increase the land ratio.

  In recent years, in order to reduce vehicle passing noise, reduction of noise generated from tires is required. Resonance sound (air column resonance) of air passing through the groove in the tread portion of the tire greatly affects the noise of the tire related to the passing noise. In order to reduce such resonance noise, it is effective to reduce the groove volume of the tread portion. Related technologies include the following.

JP 2004-262212 A

  However, a decrease in the groove volume causes a deterioration in drainage performance. In particular, a decrease in the groove volume in the crown region of the tread portion where the contact pressure is high has a great influence on the drainage performance and also causes a hydroplaning phenomenon.

  The present invention has been devised in view of the above circumstances, and based on the provision of a lug groove of a specific shape and a chamfered portion on the middle rib, the water film on the road surface is efficiently discharged, and the middle rib Providing a pneumatic tire that can improve the steering stability performance and noise performance in a well-balanced manner while maintaining wet performance by ensuring the balance of rigidity and reducing air column resonance noise in the crown and shoulder main grooves The main purpose is to do.

  According to the first aspect of the present invention, in the tread portion, a pair of crown main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and an outer side in the tire axial direction of the crown main groove in the tire circumferential direction. By providing a pair of shoulder main grooves extending continuously, a pair of crown ribs extending between the pair of crown main grooves, a pair of middle ribs extending between the crown main groove and the shoulder main grooves, and the shoulder A pneumatic tire in which a pair of shoulder land portions extending between a main groove and a ground contact end is divided and a rotation direction is specified, and the width of the crown main groove is the width of the shoulder main groove 1.2 to 1.8 times, and each middle rib extends from the crown main groove toward the rear arrival side in the rotational direction at an angle of 30 to 60 degrees with respect to the tire circumferential direction, and An inner middle lug groove that terminates without communicating with the shoulder main groove, and extends from the shoulder main groove toward the first arrival side in the rotational direction at an angle of 30 to 60 degrees with respect to the tire circumferential direction, and the crown main groove An outer middle lug groove that terminates without communicating with the inner middle lug groove, and a tire axial length of the inner middle lug groove is 0.15 to 0.35 times a rib width of the middle rib, and the outer middle lug groove The length of the tire in the axial direction of the tire is 0.35 to 0.55 times the rib width of the middle rib, and the middle rib is inclined at the intersection of the rib wall surface on both sides in the tire axial direction and the tread of the middle rib. A notched chamfered portion is formed, and the chamfered portion includes an inner rib edge region on the acute angle side where the crown main groove intersects with the inner middle lug groove, and the shoulder main groove. Outside Ribuejji region of acute side where the and the outer middle lug grooves intersect, characterized in that it comprises a wide chamfer chamfering width is expanded in the tire axial direction.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the chamfer width of the wide chamfered portion of the inner rib edge region gradually increases toward the inner middle lug groove.

  The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the depth of the wide chamfered portion of the inner rib edge region gradually increases toward the inner middle lug groove.

  According to a fourth aspect of the present invention, the chamfered portion includes an inner chamfered portion formed on the tire equator side of the middle rib, and an outer middle chamfered portion formed on the grounding end side of the middle rib. The angle between the inner chamfered portion and the normal line standing on the edge of the tread surface of the middle rib is smaller than the angle between the outer middle chamfered portion and the normal line raised on the edge of the tread surface of the middle rib. The pneumatic tire according to any one of 1 to 3.

  According to a fifth aspect of the present invention, the wide chamfered portion of the outer rib edge region comprises a slope inclined inward in the tire radial direction toward the ground contact end side and the rearward arrival side in the rotational direction. This is a pneumatic tire.

  According to a sixth aspect of the present invention, the outer middle lug groove is provided with a narrow middle sipe that terminates from the inner end in the tire axial direction of the outer middle lug groove without communicating with the crown main groove. It is a pneumatic tire in any one of thru | or 5.

  The invention according to claim 7 is the pneumatic tire according to any one of claims 1 to 6, wherein the crown rib is a plain rib provided with no groove, siping or other notches.

  In the invention according to claim 8, a shoulder lug groove extending from the shoulder main groove toward the outer side in the tire axial direction toward the rear side of the tire and beyond the ground contact end is provided in the tire circumferential direction. A pneumatic tire according to any one of claims 1 to 7.

  The invention according to claim 9 is the pneumatic tire according to any one of claims 1 to 8, wherein the inner middle lug groove and the outer middle lug groove are alternately spaced in the tire circumferential direction.

  In the pneumatic tire of the present invention, the width of the crown main groove is as large as 1.2 to 1.8 times the width of the shoulder main groove. Such a crown main groove improves the drainage performance of the crown portion having a high contact pressure, and can shift the occurrence of the hydroplaning phenomenon to a higher speed region.

  The middle rib has an inner middle lug groove extending from the crown main groove toward the shoulder main groove and terminating in the rib, and a specific angle extending from the shoulder crown main groove toward the crown main groove and terminating in the rib. An angled outer middle lug groove is arranged. As described above, the inner middle lug groove and the outer middle lug groove are formed in the middle rib having a relatively high contact pressure, and therefore can be drained more efficiently. In addition, these lug grooves, by running, can pump air into the crown main shoulder and shoulder main groove, disturb the air column flow in the crown main shoulder and shoulder main groove, and reduce resonance noise. I can do it.

  Further, the middle rib is formed with a chamfered portion in which a crossing portion between a rib wall surface facing the crown main groove and the shoulder main groove on both sides in the tire axial direction and the tread surface of the middle rib is cut obliquely. Thereby, uneven wear at the rib edge of the middle rib is suppressed, and the rib rigidity is improved.

  Further, the chamfered portion has a chamfered width in the tire axial direction in an inner rib edge region on the acute angle side where the crown main groove and the inner middle lug groove intersect and an outer rib edge region on the acute angle side where the shoulder main groove and the outer middle lug groove intersect. Includes an enlarged wide chamfer. Such a wide chamfered portion can discharge water between the road surface and the middle rib more efficiently, and also increases the rigidity of the rib edge region where the contact pressure is relatively high and the rigidity is small, Generation of uneven wear can be suppressed over a long period of time, and steering stability can be improved.

  The inner middle lug groove terminates without communicating with the shoulder main groove, and the outer middle lug groove terminates without communicating with the crown main groove. This way, from the inner middle lug groove

It is an expanded view of the tread part which shows embodiment of this invention. It is an AA expanded sectional view of FIG. FIG. 2 is a development enlarged view of a portion X in FIG. 1. It is an expanded sectional view of a middle main groove and a shoulder main groove. It is a perspective view which shows a middle rib. It is BB expanded sectional drawing of FIG. It is an expanded view of the tread part which shows a comparative example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the pneumatic tire of the present embodiment (hereinafter simply referred to as “tire”) is suitably used as a tire for passenger cars, for example.

  In the tread portion 2 of the pneumatic tire of the present embodiment, a pair of crown main grooves 3 extending continuously in the tire circumferential direction on both sides of the tire equator C, and the tire axial direction outer side of the crown main grooves 3 are arranged in the tire circumferential direction. A pair of shoulder main grooves 4 extending continuously are provided. Accordingly, the tread portion 2 includes a pair of crown ribs 5 extending between the pair of crown main grooves 3, 3, a pair of middle ribs 6 extending between the crown main grooves 3 and the shoulder main grooves 4, and the shoulders. A pair of shoulder land portions 7 extending between the main groove 4 and the ground contact end Te are formed.

  Further, the tread portion 2 of the present embodiment is formed with a directional pattern in which the rotation direction R is designated in advance. This rotation direction R is displayed by, for example, characters and / or pictograms on a sidewall portion (not shown).

  The crown main groove 3 and the shoulder main groove 4 of the present embodiment form a straight line along the tire circumferential direction. Each of the main grooves 3 and 4 is desirable in that it exhibits excellent drainage performance and can suppress unstable behavior such as vehicle wobbling and single flow during braking, and can ensure stable driving performance. .

  As shown in FIG. 1, the groove width of the crown main groove 3 (the groove width perpendicular to the longitudinal direction of the groove, the same applies to other grooves hereinafter) W1 is compared with the groove width W2 of the shoulder main groove 4. The ratio W1 / W2 is 1.2 to 1.8. When the ratio W1 / W2 is less than 1.2, the drainage performance of the crown portion having a high contact pressure is deteriorated, and the hydroplaning phenomenon is likely to occur in a relatively low speed region. On the contrary, if the ratio W1 / W2 exceeds 1.8, the ground contact area and the rib rigidity of the crown portion of the tread 2 are lowered, and the steering stability is deteriorated. From such a viewpoint, the ratio W1 / W2 is preferably 1.3 to 1.7.

  Further, the groove widths W1 and W2 of the crown main groove 3 and the shoulder main groove 4 are not particularly limited as long as the above-described ratio W1 / W2 is ensured. In order to maintain the rigidity of the ribs 5 and 6 and the land portion 7, for example, for the crown main groove 3, 6.0 to 9.0% of the tread ground contact width TW is desirable. The shoulder main groove 4 is preferably 4.0 to 6.0% of the tread ground contact width TW. The main grooves 3 and 4 of the present embodiment are formed as straight grooves extending linearly in the circumferential direction with a constant groove cross-sectional shape, but can be changed to various shapes such as a wave shape and a zigzag shape.

  Here, the “tread contact width” TW is a normal state in which a normal rim is assembled with a normal rim and filled with a normal internal pressure, and a normal load is applied to the flat tire with a camber angle of 0 degrees. The distance in the tire axial direction between the ground contact ends Te and Te. Further, the dimensions and the like of each part of the tire are values in the normal state unless otherwise specified.

  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, “Standard Rim” for JATMA and “Design Rim” for TRA. For ETRTO, use "Measuring Rim".

  The “regular internal pressure” is the air pressure defined by each standard for each tire in the standard system including the standard on which the tire is based, and is “maximum air pressure” for JATMA and table for TRA. The maximum value described in TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES is "INFLATION PRESSURE" for ETRTO, but 180 kPa for tires for passenger cars.

  Furthermore, “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. “Maximum load capacity” for JATMA, “TIRE” for TRA The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is “LOAD CAPACITY” in the case of ETRTO.

  Further, as shown in FIG. 2, the groove depth D1 of the crown main groove 3 is not particularly limited, but is preferably larger than the groove depth D2 of the shoulder main groove 4. Thereby, the drainage performance of a crown part can further be improved. In the case of a passenger vehicle tire as in the present embodiment, for example, the groove depth D1 of the crown main groove 3 is about 7.0 to 10.0 mm, and the groove depth D2 of the shoulder main groove 4 is 6.5 to 9. 5 mm is preferred. Thereby, the groove volume on the shoulder side having a relatively low ground pressure is reduced, and the rigidity balance of the rib is ensured. For this reason, the high speed performance is improved. In the present embodiment, the groove depth D1 of the crown main groove 3 is set to 8.0 mm, and the groove depth D2 of the shoulder main groove 4 is set to 7.6 mm.

  Further, the arrangement positions of the crown main groove 3 and the shoulder main groove 4 are not particularly defined, but the crown main groove 3 is, for example, a tire axial distance L1 between the center line G1 and the tire equator C. However, the tread ground contact width TW is preferably 5% or more, more preferably 7% or more, preferably 14% or less, more preferably 12% or less. For the shoulder main groove 4, for example, the tire axial distance L2 between the center line G2 and the tire equator C is preferably 23% or more, more preferably 26% or more of the tread contact width TW. Preferably, it is 35% or less, more preferably 33% or less. By setting the above range, the rigidity balance between the ribs 5 and 6 and the land portion 7 can be improved, and the steering stability performance can be improved.

  As shown in FIGS. 1 and 3, each middle rib 6 is provided with an inner middle lug groove 8 that extends from the crown main groove 3 at a specific angle and terminates without communicating with the shoulder main groove 4. Each middle rib 6 is provided with an outer middle lug groove 9 extending from the shoulder main groove 4 at a specific angle and terminating without communicating with the crown main groove 3. Such middle lug grooves 8 and 9 can improve drainage performance at the middle rib 6 having a relatively high ground pressure without lowering the rigidity of the middle rib 6.

  That is, water between the middle rib 6 and the road surface is discharged to the crown main groove 3 and the shoulder main groove 4 via the inner and outer middle lug grooves 8 and 9, respectively. As a result, wet performance, particularly drainage performance during high-speed running, is improved, and in particular, the occurrence of the hydroplaning phenomenon can be shifted to a higher speed range. Further, the inner and outer middle lug grooves 8 and 9, by traveling, pump air into the crown main groove 3 and the shoulder main groove 4, and disturb the flow of the air column in the crown main groove 3 and the shoulder main groove 4. Resonance noise can be reduced. For this reason, the noise performance of the pneumatic tire of the present invention is improved.

  Moreover, as FIG.1 and FIG.3 shows, the outer side middle lug groove | channel 9 inclines in the tire axial direction inner side toward the first arrival side of angle (theta) 2 of the rotation direction R at 30-60 degree | times with respect to a tire circumferential direction. doing. Such an outer middle lug groove 9 can ensure a large actual length of the outer middle lug groove 9 while suppressing a decrease in rigidity of the middle rib 6, and thus can improve drainage performance. In order to exhibit such an action more effectively, the angle θ2 is preferably 35 degrees or more, more preferably 40 degrees or more, and preferably 55 degrees or less, more preferably 50 degrees or less.

  The outer middle lug groove 9 is assumed to have a groove width W7 of 2.0 to 5.5 mm. Thereby, both rigidity of the middle rib 6 and drainage performance can be achieved. Further, the tire axial direction length L6 of the outer middle lug groove 9 is 0.35 to 0.55 times the rib width W4 of the middle rib 6. When this ratio L6 / W4 exceeds 0.55, the rigidity of the middle rib 6 is lowered, and the steering stability performance tends to deteriorate. Conversely, if the ratio L6 / W4 is less than 0.35, the drainage performance tends not to be sufficiently improved. From such a viewpoint, the ratio L6 / W4 is preferably 0.40 or more, and more preferably 0.50 or less.

  As shown in FIG. 3, the outer middle lug groove 9 is composed of a main portion 9a extending from the shoulder main groove 4 and a width reducing portion 9b connected to the main portion 9a and gradually reducing the groove width. desirable. Thereby, the drainage performance of the middle rib 6 is securable. In addition, since the rigidity step with the middle sipe 10 provided continuously to the outer middle lug groove 9 to be described later is eliminated, the rigidity of the middle portion is ensured. In order to enhance these effects, the ratio L9 / L6 between the tire axial direction length L6 of the outer middle lug groove 9 and the tire axial direction length L9 of the width reducing portion 9b is preferably 7% or more, more preferably 10%. % Or more is desirable, preferably 23% or less, more preferably 20% or less.

  Further, as shown in FIG. 2, the depth D5 of the outer middle lug groove 9 is not particularly limited. However, the viewpoint of ensuring the drainage performance to the shoulder main groove 4 and the rigidity of the middle rib 6 is ensured. Therefore, the groove depth D5 is preferably 20% or more, more preferably 25% or more, and preferably 80% or less, more preferably 75% or less of the groove depth D2 of the shoulder main groove 4. . In particular, the groove depth D5 of the outer middle lug groove 9 is desirably gradually increased from the tire axial direction inner end 9i toward the shoulder main groove 4 in order to further enhance the above-described action. In the present embodiment, the groove depth D5 gradually increases toward the shoulder main groove 4 in the range of 2.0 mm to 5.4 mm.

  The outer middle lug groove 9 is provided with a narrow middle sipe 10 that terminates from the inner end 9 i in the tire axial direction of the outer middle lug groove 9 without communicating with the crown main groove 3. Such a middle sipe 10 is useful for adjusting the rigidity of the rib, for example, by distributing stress without impairing the rigidity of the middle rib 6 and preventing uneven wear and heat generation.

  The middle sipe 10 is preferably formed by a blade of a mold. Therefore, the groove width W8 of the middle sipe 10 is preferably 0.5 mm or more, more preferably 0.7 mm or more, and preferably 1.5 mm or less, more preferably 1.3 mm or less. Similarly, the groove depth D6 of the middle sipe 10 is preferably 1.5 mm or more, more preferably 2.0 mm or more, and preferably 5.5 mm or less, more preferably 5.0 mm or less. Further, the groove depth D6 of the middle sipe 10 is preferably the same as the depth of the inner end 9i in the tire axial direction of the outer middle lug groove 9 in order to eliminate the rigidity step of the middle rib 6. The depth D6 is 2.0 mm.

  Further, when the sum L6 + L7 of the tire axial length of the outer middle lug groove 9 and the middle sipe 10 is increased, the axial length L10 of the inner axial end 10i of the middle sipe 10 and the crown main groove 3 is reduced. The portion tends to be a starting point of damage, and conversely, when the sum L6 + L7 of the tire axial length becomes small, the above-described rib rigidity adjusting function tends to be lowered. From such a viewpoint, the sum L6 + L7 of the tire axial length is preferably 60% or more, more preferably 65% or more, and preferably 80% or less, more preferably 75% of the rib width W4 of the middle rib 6. % Or less is desirable.

  As shown in FIGS. 1 and 3, the inner middle lug groove 8 is inclined outward in the tire axial direction toward the rear arrival side in the rotational direction R at an angle θ1 of 30 to 60 degrees with respect to the tire circumferential direction. ing. Such an inner middle lug groove 8 can improve drainage performance while suppressing a decrease in rigidity of the middle rib 6. In order to exhibit such an action more effectively, the angle θ1 is preferably 35 degrees or more, more preferably 40 degrees or more, and preferably 55 degrees or less, more preferably 50 degrees or less.

  The groove width W6 of the inner middle lug groove 8 is preferably 1.8 mm or more, more preferably 2.0 mm or more in order to improve the rib rigidity of the middle rib 6 and the drainage performance to the crown main groove 3 in a balanced manner. Further, it is preferably 4.2 mm or less, more preferably 4.0 mm or less.

  Further, it is preferable that the groove width W6 of the inner middle lug groove 8 gradually increases toward the tire equator side. Thereby, water on the road surface on the crown side having a relatively high contact pressure can be smoothly discharged to the crown main groove 3, so that the drainage performance can be further improved. In addition, the shape of the outer end 8i in the tire axial direction of the inner middle lug groove 8 is not particularly limited. However, in order to alleviate stress concentration and suppress cracks and chips, a substantially arc shape in plan view is desirable. .

  Also, the tire axial direction length L3 of the inner middle lug groove 8 is 0.15 to 0.35 times the rib width W4 of the middle rib 6. When this ratio L3 / W4 exceeds 0.35, the rigidity of the middle rib 6 becomes small, and the steering stability tends to be lowered. Conversely, when the ratio L3 / W4 is less than 0.15, the drainage performance tends to deteriorate. From such a viewpoint, the ratio L3 / W4 is preferably 0.20 or more, and more preferably 0.30 or less.

  In addition, the tire axial direction length L3 of the inner middle lug groove 8 is preferably formed to be smaller than the tire axial direction length L6 of the outer middle lug groove 9. As a result, it is possible to ensure a high rib rigidity on the tire equator side where the ground pressure is large during straight traveling. Further, since the length L6 in the tire axial direction of the outer middle lug groove 9 is increased, more water from the middle rib 6 and the road surface is transferred from the shoulder main groove 4 to the grounding end side where the ground pressure is low via the shoulder lug groove 12 described later. Since it can be discharged smoothly, drainage performance is improved.

  Further, the groove depth D3 of the inner middle lug groove 8 is not particularly limited, but is preferably the groove depth D1 of the crown main groove 3 from the viewpoint of improving drainage performance and securing the rib rigidity of the middle rib 6. Is preferably 20% or more, more preferably 25% or more, and preferably 75% or less, more preferably 70% or less. It is further desirable from the above viewpoint that the groove depth D3 gradually increases from the outer end 8i in the tire axial direction of the inner middle lug groove 8 toward the crown main groove 3 side. The groove depth D3 of the inner middle lug groove 8 of the present embodiment is gradually increased from 2.0 mm to 5.4 mm toward the crown main groove 3.

  1 and 3, the inner middle lug grooves 8 and the outer middle lug grooves 9 are alternately spaced in the tire circumferential direction. Further, the inner middle lug groove 8 and the outer middle lug groove 9 have the same pitch in the tire circumferential direction. Thereby, the rigidity balance of the middle rib 6 improves more. In particular, it is desirable that the inner middle lug groove 8 is provided at a substantially middle position between the outer middle lug grooves 9 and 9 adjacent in the tire circumferential direction. Thereby, the rigidity balance of the middle rib 6 is further maintained.

  Further, as shown in FIG. 4, the middle rib 6 is formed with a chamfered portion 16 in which intersecting portions 6x and 6y between the rib wall surfaces 6a and 6b on both sides in the tire axial direction and the tread surface 6c of the middle rib 6 are cut obliquely. . The chamfered portion 16 of the present embodiment includes a middle chamfered portion 16a in which a tire circumferential crossing portion 6x between a tire equator-side rib wall surface 6a and a middle rib tread surface 6c is obliquely cut off, and a ground wall end-side rib wall surface 6b. And an outer middle chamfered portion 16b formed by obliquely cutting an intersection 6y in the tire circumferential direction with the tread surface 6c of the middle rib 6.

  Such chamfered portions 16a and 16b can alleviate stress concentration generated at the intersecting portions 6x and 6y of the middle rib 6 during traveling, suppress uneven wear, and increase the lateral rigidity of the middle rib, thereby improving steering stability performance.

  Further, as shown in FIG. 3, the chamfered portion 16 has an equal angle chamfered portion 16e having a constant chamfered width in the tire axial direction, an acute angle side where the crown main groove 3 and the inner middle lug groove 8 intersect. The inner rib edge region E1 and the shoulder main groove 4 and the outer middle lug groove 9 are provided in the outer rib edge region E2 on the acute angle side, and the chamfering width is larger than that of the equal width chamfered portion 16e. Wide chamfered portions 16c and 16d. Such inner and outer wide chamfered portions 16c and 16d discharge water between the road surface 6c and the middle rib 6 more efficiently. Further, the inner and outer wide chamfered portions 16c and 16d increase the rigidity of the rib edge regions E1 and E2 having relatively high contact pressure and low rigidity, and suppress the occurrence of edge chipping and uneven wear over a long period of time. , Can improve steering stability.

  That is, the inner middle chamfered portion 16a is formed to include an inner equal chamfered portion 16e1 and an inner wider chamfered portion 16c, and the outer middle chamfered portion 16b is separated from the outer equal width chamfered portion 16e2. And the wide chamfered portion 16d.

  As shown in FIGS. 3 and 5, it is preferable that the chamfered width W <b> 9 of the inner wide chamfered portion 16 c gradually increases toward the inner middle lug groove 8. Thereby, the water of the inner middle lug groove 8 can be efficiently discharged to the crown main groove 3 while ensuring the rib rigidity. The intersection 16x is preferably formed in an arc shape that protrudes toward the tire equator from the viewpoint of maintaining the rigidity of the middle rib 6 while ensuring the land ratio.

  The maximum chamfering width W9 of the inner wide chamfered portion 16c is preferably 30 to 60% of the tire axial direction length L3 of the inner middle lug groove 8. When the ratio W9 / L3 is too large, the rigidity in the vicinity of E1 is remarkably lowered, and the steering stability is deteriorated. Conversely, if the ratio W9 / L3 is too small, there is a risk that effective drainage performance cannot be expected. From such a viewpoint, the ratio W9 / L3 is preferably 35 to 55%.

  Further, from the same viewpoint, the chamfering length L5 of the inner wide chamfered portion 16c in the tire circumferential direction is 220 to 280%, more preferably 230 to 270% of the tire axial direction length L3 of the inner middle lug groove 8. desirable.

  The groove depth D7 of the inner wide chamfered portion 16c is preferably a shape that gradually increases toward the inner middle lug groove 8. Thereby, the water of the inner middle lug groove 8 can be efficiently discharged into the crown main groove 3 while ensuring the rib rigidity of the middle rib 6. Specifically, the maximum value of the groove depth D7 is desirably 70 to 90% of the groove depth D3 of the inner middle lug groove 8.

  Further, as shown in FIG. 3, the outer wide chamfered portion 16d is formed in a substantially trapezoidal shape in plan view, and from an inclined surface inclined inward in the tire radial direction toward the ground contact end side and the rear arrival side in the tire rotation direction. It is desirable that the shape be Thereby, rib rigidity and drainage performance are improved.

  The maximum chamfering width W10 of the outer wide chamfered portion 16d is 10 to 30% of the length L6 in the tire axial direction of the outer middle lug groove 9, more preferably from the same viewpoint as the case of the inner wide chamfered portion 16c. 15 to 25% is desirable. Further, the chamfering length L8 in the tire circumferential direction of the outer wide chamfered portion 16d is 20 to 60%, more preferably 30 to 50% of the tire axial direction length L6 of the outer middle lug groove 9.

  As shown in FIG. 4, the angle between the inner chamfered portion 16 a (that is, the inner equal chamfered portion 16 e 1 or the inner wider chamfered portion 16 c) and the normal 6 n standing at the edge of the tread surface 6 c of the middle rib 6. α1 is the same angle as the angle α2 between the outer middle chamfered portion 16b (that is, the outer equal width chamfered portion 16e2 or the outer wide chamfered portion 16d) and the normal 6n raised at the edge of the tread surface 6c of the middle rib 6. However, it is desirable to make it smaller than α2. As a result, stress on the rib wall surface 6a on the tire equator side that is mainly grounded during straight traveling and the rib wall surface 6b on the grounded end side that is mainly grounded during turning is relieved in a balanced manner, so that the rigidity of the middle rib 6 as a whole is improved. In addition, the steering stability can be kept high. For this reason, the angle α1 is preferably 30 degrees or more, more preferably 40 degrees or more, and preferably 60 degrees or less, more preferably 50 degrees or less. The angle α2 is preferably 50 degrees or more, more preferably 60 degrees or more, and preferably 80 degrees or less, more preferably 70 degrees or less. In the present embodiment, α1 is 45 degrees and α2 is 65 degrees.

  Further, as shown in FIG. 3, the groove width t1 of the inner equal-width chamfered portion 16e1 and the groove width t2 of the outer equal-width chamfered portion 16e2 are not particularly limited, and both may be equal groove widths. However, it is desirable to make t2 larger than t1 from the above viewpoint. From this point of view, the groove width t1 of the inner width chamfered portion 16e1 is preferably 0.2 mm or more, more preferably 0.3 mm or more, and preferably 1.5 mm or less, more preferably 1. 2 mm or less is desirable. Further, the groove width t2 of the outer equal width chamfered portion 16e2 is preferably 0.5 mm or more, more preferably 0.7 mm or more, and preferably 2.0 mm or less, more preferably 1.7 mm or less. .

  Further, as shown in FIG. 1, the shoulder land portion 7 has a shoulder lug groove 12 extending from the shoulder main groove 4 toward the outer side in the tire axial direction toward the tire rear landing side and beyond the ground contact edge Te. Spaced in the direction. For this reason, the water in the shoulder main groove 4 can be efficiently discharged to the grounding end side. Further, the shoulder lug groove 12 is inclined at an angle θ3 with respect to the tire circumferential direction in order to maintain smooth drainage. From this viewpoint, the angle θ3 is preferably 65 degrees or more, more preferably 70 degrees or more, and preferably 85 degrees or less, more preferably 80 degrees or less.

  Further, as shown in FIG. 3, the groove width W11 of the shoulder lug groove 12 is not particularly limited, but if it is too large, the rib rigidity of the shoulder land portion 7 is likely to be lowered. On the other hand, if the groove width W11 is too small, the water discharging effect between the shoulder land portion 7 and the road surface is deteriorated. From such a viewpoint, the groove width W11 of the shoulder lug groove 12 is preferably 5.0 mm or more, more preferably 5.5 mm or more, and preferably 6.5 mm or less, more preferably 7.0 mm or less. desirable.

  From the same viewpoint, the groove depth D9 of the shoulder lug groove 12 (shown in FIG. 2) is preferably 20% or more, more preferably 25% or more of the groove depth D2 of the shoulder main groove 4. Further, it is preferably 85% or less, more preferably 80% or less. In addition, the groove depth D9 of the shoulder lug groove 12 is preferably a shape that gradually decreases toward the ground contact end Te from the viewpoint of ensuring smooth drainage to the ground contact end Te and rigidity of the shoulder land portion 7. In the present embodiment, the groove depth D9 gradually decreases from 5.9 mm to 2.1 mm toward the ground contact Te.

  Further, as shown in FIGS. 3 and 6, the groove wall surface 12 k on the rear side of the tire rotation direction R of the shoulder lug groove 12 has an intersection between the groove wall surface 12 k and the tread surface 7 c of the shoulder land portion 7. A shoulder lug chamfer 18 is formed by cutting 7y diagonally. Thereby, rib rigidity is ensured and damages, such as a rib chip, can be controlled.

  The angle α5 between the shoulder lug chamfered portion 18 and the normal line 7n standing at the edge of the tread surface 7c of the shoulder land portion 7 is preferably formed at an angle of 60 to 70 degrees. Thereby, the above-mentioned rib chipping or the like can be suppressed even during turning with a large load stress. In addition, it is desirable that the chamfered portion as described above is also provided on the groove wall surface 12s on the first arrival side in the tire rotation direction of the shoulder lug groove 12 from the viewpoint of reducing stress concentration.

  Further, as shown in FIG. 1, the crown rib 5 is preferably a plain rib not provided with grooves, siping or other cuts. Since such a crown rib 5 continuously extends in the tire circumferential direction with a constant width, the rigidity distribution is maintained uniformly and high. As a result, uneven wear is suppressed particularly in the crown rib 5 having a high contact pressure, and a dry road surface. It is expected that the handling stability will improve.

  As shown in FIGS. 3 and 4, the crown rib 5 has a chamfered chamfer in which the entire area of the intersecting portion 5x between the circumferential rib wall surface 5a of the crown rib 5 and the tread surface 5c of the crown rib 5 is cut obliquely. Part 15 is formed. Further, the shoulder land portion 7 is formed with a shoulder chamfered portion 17 in which an intersection portion 7x between the circumferential land portion wall surface 7a of the shoulder land portion 7 and the tread surface 7c of the shoulder land portion 7 is obliquely cut.

  As shown in FIG. 1, the tread portion 2 of the present embodiment has an inner middle lug groove 8, an outer middle lug groove 9, and a shoulder lug groove 12, except that it is shifted by a distance h in the tire circumferential direction. It is substantially line symmetric about the equator C.

  Although the pneumatic tire of the present invention has been described in detail above, it is needless to say that the present invention can be implemented in various forms without being limited to the specific embodiment described above.

  In order to confirm the effect of the present invention, a 235 / 50R18 passenger car tire having the pattern of FIG. 1 and based on the specifications of Table 1 was manufactured. Each test tire was mounted on an imported vehicle having a displacement of 3500 cc with a rim 8J and an internal pressure of 200 kPa, and the steering stability performance (dry asphalt road surface and wet asphalt road surface) and passing noise were tested.

  In Comparative Examples 1 and 2, the pattern shown in FIG. 5 was adopted. The parameters other than those shown in Table 1 are all the same. The common specifications are as follows.

Tread contact width TW: 186mm
Crown main groove width W1: 16.3 mm
Shoulder main groove width W2: 10.9mm
Crown main groove arrangement L1 / TW: 8%
Shoulder main groove arrangement L2 / TW: 32%
Crown depth D1: 8.0mm
Shoulder main groove depth D2: 7.6 mm
Inner middle lug groove width W6: 2.0 to 3.5 mm
Outer middle lug groove width W7: 3.0 to 4.0 mm
Inner middle lug groove depth D3: 2.0 to 5.4 mm
Outer middle lug groove depth D5: 2.0 to 5.4 mm
Shoulder lug groove width W11: 4.0 to 4.5 mm
Shoulder lug groove depth D9: 2.1 to 5.9 mm
Middle sipe groove width W8: 0.8mm
Middle sipe groove depth D6: 2.0mm
Inner middle chamfered portion 16a angle α1: 45 degrees Outer middle chamfered portion 16b angle α2: 65 degrees The test method is as follows.

<Steering stability>
With the above test vehicle, one driver ran on the dry asphalt road surface and wet asphalt road test course. The characteristics relating to handle responsiveness, rigidity, grip, etc. were evaluated by a driver's sensory evaluation with a score of Comparative Example 1 being 100. The larger the value, the better.

<Passing noise test>
In accordance with the actual vehicle coasting test specified in JASO / C / 606, the vehicle travels on a straight test course (asphalt road surface) at a speed of 50 m at a passing speed of 60 km / h, and from the traveling center line at the midpoint of the course. The maximum level of passing noise dB (A) was measured with a stationary microphone installed at a position of 7.5 m on the side and 1.2 m from the road surface. The results are displayed as an index with Comparative Example 1 being 100, and the larger the index, the smaller the passing noise and the better.
Table 1 shows the test results.

  As a result of the test, it can be confirmed that the running performance on the wet asphalt road surface of the tire of the example is significantly improved as compared with the comparative example. It was also confirmed that there was no problem with dry asphalt road surface and passing noise performance.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Crown main groove 4 Shoulder main groove 5 Crown rib 6 Middle rib 6a Middle rib rib wall surface 6b Middle rib rib wall surface 6c Middle rib tread 7 Shoulder land 8 Inner middle lug groove 9 Outer middle lug groove 16 Chamfer 16c Wide chamfered portion 16d Wide chamfered portion C Tire equator E1 Inner rib edge region E2 Outer rib edge region Te Grounding end

Claims (9)

A pair of crown main grooves extending continuously in the tire circumferential direction on both sides of the tire equator and a pair of shoulder main grooves extending continuously in the tire circumferential direction on the outer side in the tire axial direction of the crown main groove are provided on the tread portion. A pair of crown ribs extending between the pair of crown main grooves, a pair of middle ribs extending between the crown main groove and the shoulder main grooves, and a pair of between the shoulder main grooves and the grounding end. It is a pneumatic tire that is separated from the shoulder land and whose rotation direction is specified.
The width of the crown main groove is 1.2 to 1.8 times the width of the shoulder main groove,
Each middle rib has an inner middle lug extending from the crown main groove toward the rear arrival side in the rotational direction at an angle of 30 to 60 degrees with respect to the tire circumferential direction and terminating without communicating with the shoulder main groove. A groove and an outer middle lug groove extending from the shoulder main groove toward the first arrival side in the rotational direction at an angle of 30 to 60 degrees with respect to the tire circumferential direction and terminating without communicating with the crown main groove. As
The tire axial length of the inner middle lug groove is 0.15 to 0.35 times the rib width of the middle rib,
The tire axial length of the outer middle lug groove is 0.35 to 0.55 times the rib width of the middle rib,
Moreover, the middle rib is formed with a chamfered portion in which an intersecting portion between a rib wall surface on both sides in the tire axial direction and a tread surface of the middle rib is cut obliquely,
The chamfered portion includes an inner rib edge region on the acute angle side where the crown main groove and the inner middle lug groove intersect and an outer rib edge region on the acute angle side where the shoulder main groove and the outer middle lug groove intersect with each other in the tire axial direction. A pneumatic tire comprising a wide chamfered portion with an enlarged chamfer width.   The pneumatic tire according to claim 1, wherein a chamfering width of the wide chamfered portion of the inner rib edge region gradually increases toward the inner middle lug groove.   The pneumatic tire according to claim 1 or 2, wherein the depth of the wide chamfered portion of the inner rib edge region gradually increases toward the inner middle lug groove. The chamfered portion includes an inner middle chamfered portion formed on the tire equator side of the middle rib and an outer middle chamfered portion formed on the grounded end side of the middle rib,
The angle between the inner chamfered portion and the normal line standing at the edge of the tread surface of the middle rib is smaller than the angle between the outer middle chamfered portion and the normal line raised at the edge of the tread surface of the middle rib. The pneumatic tire according to any one of 1 to 3.   The pneumatic tire according to any one of claims 1 to 4, wherein the wide chamfered portion of the outer rib edge region is a slope inclined inward in the tire radial direction toward the ground contact end side and the rear arrival side in the rotation direction.   6. The air according to claim 1, wherein the outer middle lug groove is provided with a narrow middle sipe that terminates from the inner end in the tire axial direction of the outer middle lug groove without communicating with the crown main groove. Enter tire.   The pneumatic tire according to any one of claims 1 to 6, wherein the crown rib is a plain rib not provided with a groove, siping or other notches.   8. The shoulder land portion is provided with shoulder lug grooves extending in the tire circumferential direction from the shoulder main groove toward the outer side in the tire axial direction and extending beyond the tire landing side and beyond the ground contact end. Pneumatic tire described in 2.   The pneumatic tire according to any one of claims 1 to 8, wherein the inner middle lug groove and the outer middle lug groove are alternately spaced in the tire circumferential direction.

Images