JP2014141165A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve circularity of a tread part and drainage performance in excellent balance.SOLUTION: In a pneumatic tire, a tread part 2 is provided with a pair of main grooves 3 extending continuously in the tire circumferential direction along both sides of a tire equator C, and a plurality of lug grooves 4 extending from the main grooves 3 toward the tire axial direction outside and ending at the furthermore inside in the tire axial direction than the tread ground contact end Te. The groove width of each lug groove 4 is 3-11% of a tread ground contact width TW. Each lug groove 4 includes a shallow bottom part 11 linking to the main groove 3 and having a small groove depth, a deep bottom part 13 having a larger groove depth than the shallow bottom part 11, and a taper part 12 connecting the deep bottom part 13 to the shallow bottom part 11 and having a groove depth reducing gradually toward the shallow bottom part 11.

Description

  The present invention relates to a pneumatic tire in which the roundness of a tread portion and drainage performance are improved in a well-balanced manner.

  Conventionally, a pneumatic tire is known in which a main groove extending continuously in the tire circumferential direction and a lug groove extending from the main groove toward the outer side in the tire axial direction are provided. Since such a pneumatic tire collects the water film between the land portion of the tread portion and the road surface by the lug groove and discharges it to the outside of the tire through the main groove, it exhibits high drainage performance.

  However, when manufacturing such a pneumatic tire by vulcanization molding, the groove forming projection of the vulcanization mold for forming the lug groove moves the unvulcanized tread rubber to the tread surface side of the tread portion. For this reason, the vulcanized tire has a problem that the rubber thickness of the land portion in the vicinity of the lug groove is larger than the designed rubber thickness, and the roundness of the tread portion is deteriorated.

JP 2009-196431 A

  The present invention has been devised in view of the actual situation as described above, and based on defining the groove width of the lug groove and the groove shape within a certain range, the vicinity of the lug groove at the time of vulcanization molding is provided. The main purpose is to provide a pneumatic tire in which the deformation of the tread rubber is reduced and the roundness of the tread portion and the drainage performance are improved in a well-balanced manner.

  According to the first aspect of the present invention, the tread portion includes a pair of main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and extending from the main grooves toward the outer side in the tire axial direction and tread grounding. A pneumatic tire provided with a plurality of lug grooves that terminate on the inner side in the tire axial direction from the end, wherein the lug groove has a groove width of 3 to 11% of a tread contact width, and the lug groove Is connected to the main groove and has a shallow bottom portion, a deep bottom portion having a groove depth larger than the shallow bottom portion, and a joint between the deep bottom portion and the shallow bottom portion, and the groove depth toward the shallow bottom portion. And a taper portion that gradually decreases.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the lug groove is inclined at an angle of 40 to 60 degrees with respect to the tire circumferential direction.

  The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the groove depth of the shallow bottom portion is 30 to 60% of the groove depth of the deep bottom portion.

  The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 3, wherein the shallow bottom portion has a length in the tire axial direction of 5 to 15% of the tread contact width.

  The invention according to claim 5 is the pneumatic tire according to any one of claims 1 to 4, wherein the tapered portion has a length in a tire axial direction of 10 to 20% of the tread contact width.

  The invention according to claim 6 is the pneumatic tire according to any one of claims 1 to 5, wherein the lug groove has a groove depth of 5 mm or more.

  The invention according to claim 7 is the pneumatic tire according to any one of claims 1 to 6, wherein 10 to 40 lug grooves are provided on a tire circumference.

  The pneumatic tire of the present invention includes a pair of main grooves extending continuously in the tire circumferential direction on both sides of the tire equator in the tread portion, extending outward from the main groove in the tire axial direction, and extending beyond the tread grounding end. A plurality of lug grooves that terminate in the inner direction are provided. The lug groove is formed with a groove width of 3 to 11% of the tread ground contact width. Such a lug groove efficiently discharges a water film between the land portion of the tread portion and the road surface to the main groove to improve drainage performance.

  The lug groove is connected to the main groove and has a shallow bottom portion having a small groove depth, a deep bottom portion having a groove depth larger than the shallow bottom portion, and the deep bottom portion and the shallow bottom portion connected to each other and the groove depth toward the shallow bottom portion. And a taper portion that gradually decreases. In such a lug groove, the tread rubber pressed by the groove forming projection of the vulcanization mold for forming the deep bottom portion smoothly moves toward the shallow bottom portion through the tapered portion at the time of vulcanization molding. At this time, the pressed tread rubber flows into, for example, a gap of the tread rubber that forms a tapered portion or a shallow bottom portion. Further, the tread rubber formed by the groove forming protrusions of the vulcanization mold is largely pressed in the region where the main groove and the lug groove are continuous. For this reason, by setting the portion where the lug groove is connected to the main groove as a shallow bottom portion, the pressing force of the tread rubber is reduced, and the amount of movement of the rubber is reduced. Therefore, the rubber thickness after vulcanization molding of the land portion in the vicinity of the lug groove is suppressed from becoming larger than the designed rubber thickness, and the roundness of the tread portion is improved.

It is an expanded view of the tread part which shows one Embodiment of this invention. (A) is XX sectional drawing of FIG. 1, (b) is sectional drawing of the longitudinal direction of the lug groove of other embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire of this embodiment (hereinafter, simply referred to as “tire”) is preferably used for, for example, a passenger car, and the tread portion 2 is formed on both sides of the tire equator C. A pair of main grooves 3 extending continuously in the tire circumferential direction, and a plurality of lug grooves 4 extending from each main groove 3 toward the tire axial direction outer side and terminating at the inner side in the tire axial direction than the tread ground contact end Te; , And an inclined groove 5 disposed between the lug grooves 4 and 4 adjacent to each other in the tire circumferential direction.

  Thus, the tread portion 2 of the present embodiment includes a single center land portion 6 divided by the pair of main grooves 3 and 3 and a pair of shoulders divided by the main groove 3 and the tread grounding end Te. Land part 7 is arranged.

  The “tread grounding end” Te is grounded on a flat surface at a camber angle of 0 ° by applying a normal load to an unloaded normal tire that is assembled with a normal rim (not shown) and filled with a normal internal pressure. It is determined as the ground contact position on the outermost side in the tire axial direction when it is used. A distance in the tire axial direction between the tread ground contact Te and Te is determined as a tread ground contact width TW. When there is no notice in particular, the dimension of each part of a tire is the value measured in the said normal state.

  The “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. “Standard Rim” for JATMA, “Design Rim” for TRA For ETRTO, "Measuring Rim". In addition, the “regular internal pressure” is an air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. 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.

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

  The main groove 3 of the present embodiment has a linear shape along the tire circumferential direction. Such a main groove 3 smoothly drains water in the groove backward in the tire rotation direction. For this reason, drainage performance improves. The main groove 3 may be a groove extending in a wave shape or a zigzag shape, for example. The main grooves 3 are preferably arranged symmetrically about the tire equator C in order to improve drainage performance with good balance on both sides of the tire equator C.

  About the groove width of the main groove 3 (the groove width measured in the direction perpendicular to the groove center line, hereinafter the same applies to other grooves) W1 and the groove depth D1 (shown in FIG. 2A) Various definitions can be made in accordance with common practice. However, when these groove widths W1 or groove depths D1 are reduced, drainage performance may be deteriorated. Conversely, when the groove width W1 or the groove depth D1 is increased, the areas of the tread surfaces of the center land portion 6 and the shoulder land portion 7 are decreased, and the grip performance may be deteriorated. For this reason, the groove width W1 of the main groove 3 is, for example, preferably 4% or more, more preferably 5% or more, preferably 8% or less, more preferably 7% or less of the tread ground contact width TW. The groove depth D1 is preferably 5 mm or more, more preferably 6 mm or more, and preferably 10 mm or less, more preferably 9 mm or less.

  In order to ensure the rigidity in the tire axial direction of the center land portion 6 and the shoulder land portion 7 with a good balance, the tire axial distance L1 between the groove center line G1 of the main groove 3 and the tire equator C is equal to the tread ground contact width TW. 5-13% is desirable.

  The main groove 3 may be provided on the groove wall surface extending in the tire circumferential direction with a chamfered portion (not shown) obtained by obliquely notching the intersection between the groove wall surface and the shoulder land portion 7 or the tread surface of the center land portion 6. .

  In the present embodiment, the lug groove 4 is inclined to one side with respect to the tire circumferential direction (in FIG. 1, it is inclined upward toward the outer side in the tire axial direction). Such a lug groove 4 can smoothly drain the water in the groove to the main groove 3.

  The lug groove 4 is defined to have a groove width W2 of 3 to 11% of the tread ground contact width TW. That is, when the groove width W2 of the lug groove 4 is less than 3%, the water film between the shoulder land portion 7 and the road surface cannot be efficiently discharged to the main groove 3, and the drainage performance is deteriorated. When the groove width W2 of the lug groove 4 exceeds 11%, the area of the tread surface of the shoulder land portion 7 is reduced, and the grip performance is deteriorated. Moreover, since the groove area is increased, the aggressiveness of the appearance of the tread portion 2 is deteriorated. For this reason, the groove width W2 of the lug groove 4 is preferably 5% or more of the tread ground contact width TW, and preferably 8% or less. The numerical range of the groove width W2 is specified by the maximum width of the lug groove 4.

  In this embodiment, the groove width W2 of the lug groove 4 is gradually increased toward the main groove 3 side. Thereby, the water in the groove is further smoothly drained to the main groove 3 side. Moreover, the rigidity of the shoulder land portion 7 is ensured to be high.

  When the angle θ1 with respect to the tire circumferential direction is large, the drainage resistance during straight traveling increases and the drainage performance during straight traveling may deteriorate. When the angle θ1 of the lug groove 4 with respect to the tire circumferential direction is small, the drainage resistance during cornering increases and the drainage performance during cornering may deteriorate. For this reason, the angle θ1 of the lug groove 4 with respect to the tire circumferential direction is preferably 40 ° or more, more preferably 45 ° or more, preferably 60 ° or less, more preferably 55 ° or less. The angle θ1 of the lug groove 4 is defined by the angle formed by the tangent to the groove center line G2 of the lug groove 4 and the tire circumferential direction line. Further, the groove center line G2 of the lug groove 4 is a line formed by joining the midpoint of the length of the lug groove 4 in the tire circumferential direction. The vicinity of the outer end 4e of the lug groove 4 in the tire axial direction has little influence on the drainage performance, so the angle θ1 of the lug groove 4 is 80, which is the length L2 of the main groove 3 to the lug groove 4 in the tire axial direction. It may be formed within the above range in a range exceeding%.

  Although not particularly limited, the length L2 of the lug groove 4 in the tire axial direction is the length of the shoulder land portion 7 in the tire axial direction from the viewpoint of ensuring a good balance between grip force and drainage performance during cornering. The thickness Ls is preferably 75% or more, more preferably 80% or more, preferably 95% or less, more preferably 90% or less.

  As shown in FIG. 2 (a), which is an XX cross-sectional view of FIG. 1, the lug groove 4 is formed with a groove depth D2 of preferably 5 mm or more in order to ensure high drainage performance. In addition, when groove depth D2 is large, the rigidity of shoulder land part 7 may fall, and there exists a possibility that grip performance may deteriorate. For this reason, the groove depth D2 of the lug groove 4 is preferably 4.0 mm or less.

  It is desirable that 10 to 40 lug grooves 4 are provided on the tire circumference of one shoulder land portion 7. That is, when the number of the lug grooves 4 is small, the drainage performance may be deteriorated. When the number of lug grooves 4 is large, the tread surface of the shoulder land portion 7 becomes small, the frictional force with the road surface decreases, and the grip performance may be deteriorated. In addition, the aggressiveness of the appearance may be deteriorated. For this reason, the lug grooves 4 are preferably provided with 15 or more and 35 or less on the tire circumference.

  The lug groove 4 is connected to the main groove 3 and has a shallow bottom portion 11 having a small groove depth, a deep bottom portion 13 having a groove depth larger than the shallow bottom portion 11, and the deep bottom portion 13 and the shallow bottom portion 11. And a tapered portion 12 whose depth gradually decreases toward the shallow bottom portion 11. In such a lug groove 4, during the vulcanization molding, the tread rubber pressed by the groove molding projection of the vulcanization mold for molding the deep bottom portion 13 smoothly moves to the shallow bottom portion 11 side through the taper portion 12. To do. At this time, the pressed tread rubber flows into the gap of the tread rubber forming the tapered portion 12 and the shallow bottom portion 11, for example. Further, the tread rubber formed by the groove forming projections of the vulcanization mold is largely pressed in the region where the main groove 3 and the lug groove 4 are continuous. For this reason, by setting the portion where the lug groove is connected to the main groove as a shallow bottom portion, the pressing force of the tread rubber is reduced, and the amount of movement of the rubber is reduced. Therefore, since the rubber thickness after vulcanization molding of the shoulder land portion 7 in the vicinity of the lug groove 4 is suppressed from being larger than the designed rubber thickness, the roundness of the tread portion 2 is improved.

  The groove depth D3 of the shallow bottom portion 11 is preferably 30% or more, more preferably 35% or more, preferably 60% or less, more preferably 55% or less, of the groove depth D4 of the deep bottom portion 13. When the groove depth ratio D3 / D4 is large, the tread rubber pressed by the groove forming projection of the vulcanization mold for forming the deep bottom portion 13 moves to the tread surface side of the shoulder land portion 7 in the vicinity of the shallow bottom portion 11. However, the above-described action may not be effectively exhibited. On the contrary, when the ratio D3 / D4 of the groove depth is small, the drainage resistance in the groove from the deep groove portion 13 to the main groove 3 is increased, and the drainage performance may be deteriorated.

  The length L3 (shown in FIG. 1) of the shallow bottom portion 11 in the tire axial direction is preferably 5% or more, more preferably 7% or more, and preferably 15% or less, more preferably 13% of the tread contact width TW. It is as follows. If the length L3 of the shallow bottom portion 11 in the tire axial direction exceeds 15%, the drainage performance may be deteriorated. When the length L3 of the shallow bottom part 11 in the tire axial direction is less than 5%, the gap of the tread rubber for molding the shallow bottom part 11 becomes small, and the tread rubber pushed by the groove forming protrusion from the deep bottom part 13 at the time of tire molding. However, there is a possibility that the tread portion 2 may move to the tread 2n side.

  The length L4 (shown in FIG. 1) of the tapered portion 12 in the tire axial direction is preferably 10% or more, more preferably 12% or more, preferably 20% or less, more preferably 18% of the tread contact width TW. It is as follows. When the length L4 in the tire axial direction of the taper portion 12 is less than 10%, the rigidity step between the shoulder land portion 7 near the shallow bottom portion 11 and the shoulder land portion 7 near the deep bottom portion 13 becomes large, and the grip performance deteriorates. There is a fear. When the length L4 of the taper portion 12 in the tire axial direction exceeds 20%, the length L3 of the shallow bottom portion 11 in the tire axial direction or the length of the deep bottom portion in the tire axial direction becomes small, and the drainage performance or the perfect circle of the tire is reduced. There is a risk that the degree will deteriorate.

  In order to effectively exhibit the above-described action, the length L4 of the tapered portion 12 in the tire axial direction is preferably 1.2 times or more, more preferably 1.3 times the length L3 of the shallow bottom portion 11 in the tire axial direction. It is more than twice, preferably 1.7 times or less, more preferably 1.6 times or less.

  In this embodiment, the groove bottom 12s of the tapered portion 12 extends smoothly in a straight line in a tire meridian cross-sectional view. Such a tapered portion 12 smoothly moves the tread rubber pressed from the deep bottom portion 13 toward the shallow bottom portion 11 side. The shape of the groove bottom of the tapered portion 12 is not limited to a linear shape, and as shown in FIG. 2B, an inner convex surface 12a that is convex inward in the tire radial direction, and an inflection with the inner convex surface 12a. A curved shape including two arcs r connected to the outer convex surface 13b which is continuous through the point m and protrudes outward in the tire radial direction may be used. Such a tapered portion 12 further reduces the rigidity step of the shoulder land portion 7 and ensures a higher grip performance. Note that the curvature of the arc r may be the same or different.

  As shown in the tread development view of FIG. 1, the inclined groove 5 is arranged in a longitudinal direction between the first inclined groove 5A extending in an arc shape, between the first inclined groove 5A and the lug groove 4 in the tire circumferential direction. The second inclined groove 5 </ b> B that bends substantially in the middle of each other and the third inclined groove 5 </ b> C whose both ends terminate in the shoulder land portion 7. The first inclined groove 5A and the second inclined groove 5B have one end terminated in the shoulder land portion 7 and the other end terminated outside the tread ground contact end Te in the tire axial direction.

  As described above, the shoulder land portion 7 of the present embodiment is formed as a rib extending continuously in the tire circumferential direction in which at least one end of the lug groove 4 and the inclined groove 5 terminates in the shoulder land portion 7. For this reason, the rigidity of the shoulder land portion 7 is ensured and the grip performance is maintained high. Further, the lug groove 4 and the inclined groove 5 effectively drain the water film between the tread surface of the shoulder land portion 7 and the road surface. Therefore, high drainage performance is ensured.

  Each of the lug grooves 4 and the inclined grooves 5 may be provided with a chamfered portion (not shown) in which a crossing portion between the groove wall surface and the tread surface of the shoulder land portion 7 is obliquely cut out on the groove wall surface extending in the tire axial direction. .

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention is changed and implemented in various aspects, without being limited to said specific embodiment.

A pneumatic tire of size 245 / 40R18 having the basic pattern of FIG. 1 was prototyped based on the specifications in Table 1, and the drainage performance of each sample tire, the roundness of the tread portion, the grip performance and the appearance were tested. The common specifications for each tire are as follows. Except for the grooves described in Table 1, the groove width of each groove, the length in the tire axial direction, and the angle are as shown in FIG.
Tread contact width TW: 212mm
<Main groove>
Groove depth D1: 7.5mm
<Rug groove>
FIG. 2A is a diagram showing a cross-sectional shape of the tapered portion.
<Others>
Groove depth of the first inclined groove: 6.1 mm
Groove depth of second inclined groove: 6.1 mm
Groove depth of third inclined groove: 6.1 mm
The test method is as follows.

<Drainage performance>
The sample tires were installed on all wheels of a passenger car (displacement of 3000 cc, domestic FR car) under the following conditions, and a puddle with a water depth of 10 mm and a length of 20 m was provided on an asphalt road surface with a radius of 100 m and a straight 400 m asphalt road surface. Driving at high speed on the test course, the driver's sensory evaluation was performed for steering stability and straight running stability. The results are displayed in a 6-point method with 6 points being the perfect score.
Rims: 18 x 8.5J
Internal pressure: 230 kPa (all wheels)

<Grip performance>
With the above test vehicle, the above test course on the dry asphalt road surface was ridden by one driver, and the grip performance when traveling straight and turning was evaluated by sensory evaluation of the driver. The results are displayed in a 6-point method with 6 points being the perfect score.

<Appearance>
With the test tires mounted on the test vehicle, the appearance of the tread portion was evaluated by 10 testers. The results are displayed in a 6-point method with 6 points being the perfect score.

<Roundness of tread part>
RRO (radial run-out) and RFV (radial force variation) were measured under the following conditions in accordance with the uniformity test conditions of JASO C607: 2000 using a force variation testing machine (sample tires, 20 tires each). Average value). Evaluation is calculated by taking the average value of the reciprocal of RRO and RFV in the high speed range of Example 1 as 100, less than 50 1 point, 50 or more and less than 60 2 points, 60 or more and less than 70 3 points, 70 or more and less than 80 4 points, 80 to less than 90 5 points, and 90 or more 6 points.
Rims: 18 x 8.5J
Internal pressure: 230 kPa
Load: 5.72kN
Speed: 80km / h
The test results are shown in Table 1.

The evaluation of the test is evaluated by the total of each test. In other words, an example with one point of evaluation is inferior in overall evaluation to an example without one point of evaluation.
As a result of the test, the tires of the examples improved each performance in a well-balanced manner as compared with the comparative examples.

2 tread portion 3 main groove 4 lug groove 11 shallow bottom portion 12 taper portion 13 deep bottom portion C tire equator Te tread grounding end TW tread grounding width

Claims (7)

In the tread portion, a pair of main grooves extending continuously in the tire circumferential direction on both sides of the tire equator,
A pneumatic tire provided with a plurality of lug grooves extending from the main groove toward the outer side in the tire axial direction and terminating at the inner side in the tire axial direction from the tread grounding end,
The lug groove has a groove width of 3 to 11% of the tread contact width, and the lug groove is connected to the main groove and has a shallow bottom portion having a small groove depth, and a deep bottom portion having a groove depth larger than the shallow bottom portion. And a tapered portion that joins the deep bottom portion and the shallow bottom portion, and has a groove depth that gradually decreases toward the shallow bottom portion.   The pneumatic tire according to claim 1, wherein the lug groove is inclined at an angle of 40 to 60 ° with respect to the tire circumferential direction.   The pneumatic tire according to claim 1 or 2, wherein a groove depth of the shallow bottom portion is 30 to 60% of a groove depth of the deep bottom portion.   The pneumatic tire according to any one of claims 1 to 3, wherein the shallow bottom portion has a tire axial length of 5 to 15% of the tread contact width.   The pneumatic tire according to any one of claims 1 to 4, wherein the tapered portion has a length in a tire axial direction of 10 to 20% of the tread contact width.   The pneumatic tire according to any one of claims 1 to 5, wherein the lug groove has a groove depth of 5 mm or more.   The pneumatic tire according to claim 1, wherein 10 to 40 lug grooves are provided on the tire circumference.

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