Patent Application
20170210176
The present invention relates to a pneumatic tire capable of exerting excellent running performance on snowy/icy roads while maintaining the steering stability.
Japanese Patent Application Publication No. 2014-184948 (Patent Literature 1) discloses a pneumatic tire provided with a zigzag main groove having a zigzag periodical pattern. Compared with a straight main groove, a zigzag main groove is increased in the length of the edges, and thereby can increase a scratch frictional force.
In the pneumatic tire disclosed in Patent Literature 1, if the zigzag pitches or pitch lengths of the zigzag main groove are decreased in order to further increase the frictional force on snowy/icy roads, then a land region (blocks, rib) adjacent to the main groove becomes more likely to deform, therefore, the steering stability tends to deteriorate.
The present invention was made in view of the above, and a primary object thereof is to provide a pneumatic tire in which, by improving the configuration of a zigzag main groove, excellent running performance on snowy/icy roads can be obtained without sacrificing the steering stability.
According to the present invention, a pneumatic tire comprises:
a tread portion provided with at least one main groove extending continuously in the tire circumferential direction, wherein
the or each main groove has a zigzag periodical pattern formed by repeatedly circumferentially arranging a first oblique segment and a second oblique segment as a repeating unit defining one zigzag pitch,
the first oblique segment extends without being bent, and
the second oblique segment extends in a bent manner.
In the pneumatic tire according to the present invention, it is preferable that the first oblique segment is straight.
In the pneumatic tire according to the present invention, the first oblique segment may be arc-shaped.
In the pneumatic tire according to the present invention, it is preferable that the second oblique segment comprises a pair of second portions inclined to the opposite direction to the first portion, and
a first portion disposed therebetween and inclined to the same direction as the first oblique segment.
In the pneumatic tire according to the present invention, it is preferable that the second portions are longer than the first portion.
In the pneumatic tire according to the present invention, it is preferable that a maximum amplitude in the tire axial direction of the zigzag main groove is not greater than 3.0 times a maximum groove width of the zigzag main groove.
In the pneumatic tire according to the present invention, it is preferable that an amplitude of the second oblique segment is 0.30 to 0.75 times an amplitude of the zigzag configuration of the main groove.
In the pneumatic tire according to the present invention, it is preferable that the above-mentioned at least one main groove includes a pair of crown main grooves disposed in a tread crown portion,
the crown main grooves are arranged such that phases of the zigzag configurations thereof are aligned, and
a center land region defined between the crown main grooves is divided into a plurality of blocks by center transverse grooves connecting between the first oblique segments of one of the crown main grooves and the first oblique segments of the other crown main groove.
In the pneumatic tire according to the present invention, it is preferable that the center transverse grooves are inclined to the opposite direction to the first oblique segments.
In this application including specification and claims, various dimensions, positions and the like of the tire refer to those under a normally inflated unloaded condition of the tire unless otherwise noted.
The normally inflated unloaded condition is such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load.
The undermentioned normally inflated loaded condition is such that the tire is mounted on the standard wheel rim and inflated to the standard pressure and loaded with the standard tire load.
The standard wheel rim is a wheel rim officially approved or recommended for the tire by standards organizations, i.e. JATMA (Japan and Asia), T&RA (North America), ETRTO (Europe), TRAA (Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC (India) and the like which are effective in the area where the tire is manufactured, sold or used.
The standard pressure and the standard tire load are the maximum air pressure and the maximum tire load for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list.
For example, the standard wheel rim is the “standard rim” specified in JATMA, the “Measuring Rim” in ETRTO, the “Design Rim” in TRA or the like. The standard pressure is the “maximum air pressure” in JATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given in the “Tire Load Limits at various Cold Inflation Pressures” table in TRA or the like. The standard load is the “maximum load capacity” in JATMA, the “Load Capacity” in ETRTO, the maximum value given in the above-mentioned table in TRA or the like.
The tread edges Te are the axial outermost edges of the ground contacting patch which occurs under the normally inflated loaded condition when the camber angle of the tire is zero.
The tread width TW is the width measured under the normally inflated unloaded condition, as the axial distance between the tread edges Te determined as above.
An embodiment of the present invention will now be described in detail in conjunction with accompanying drawings. The present invention can be applied to various tires, and suitably applied to a winter tire. The pneumatic tire 1 in this embodiment is a winter tire for passenger cars.
The tread portion 2 of the pneumatic tire 1 is shown in
As shown in
The main grooves 3 in this example include
a pair of crown main grooves 5 provided in a crown portion of the tread portion 2 and
a shoulder main groove 6 disposed axially outside each of the crown main grooves 5.
As shown in
The first oblique segment 11 extends without being bent whereas the second oblique segment is bent in a zigzag manner and has a second amplitude.
The crown main groove 5 configured as such can suppress excessive deformation of the land region partitioned by the main groove owing to the first oblique segment 11 extending without being bent, therefore, it is possible to maintain the steering stability.
On the other hand, the second oblique segment 12 extends in a bent manner and has a longer edge, therefore, it is possible to provide large frictional force on snowy/icy roads. Thereby, the pneumatic tire according to the present invention can exert excellent running performance on snowy/icy roads while maintaining the steering stability.
Although specific configurations to further exert the above described effects will now be described in detail, the present invention is not limited to such specific configurations.
It is preferable that the first oblique segment 11 is straight or arc-shaped. More preferably, the first oblique segment 11 is configured in the form of a smoothly curved arc which is convexed toward the inside in the tire axial direction. The first oblique segment 11 configured as such can deforms toward the tire equator C when running on snow-covered roads and compresses the snow therein firmly. Moreover, the first oblique segment 11 is easy to expand and contract in its length before and after the contact with the ground, therefore, it is helpful to effectively discharge the snow in the groove.
In order to increase the length of the edges while maintaining the steering stability, the angle θ1 (not shown) of the first oblique segment 11 with respect to the tire circumferential direction is preferably set in a range from 15 to 25 degrees, for example. The length L1 of the first oblique segment 11 is set in a range from 0.10 to 0.25 times the tread width TW, for example.
As shown in
The first portion 16 is disposed in the vicinity of the center of the second oblique segment 12 in the tire circumferential direction. The first portion 16 is inclined to the same direction as the first oblique segment 11.
The second portions 17 are inclined to the opposite direction to the first portion 16 with respect to the tire circumferential direction.
It is preferable that each of the first portion 16 and the second portion 17 is shorter than the first oblique segment 11. For example, the length L2 of the first portion 16 is preferably set in a range from 0.10 to 0.20 times the length L1 of the first oblique segment 11. The length L3 of the second portion 17 is preferably set in a range from 0.30 to 0.40 times the length L1 of the first oblique segment 11.
The first portion 16 and the second portion 17 configured as such can increase the length of the edges effectively while suppressing the deformation of the land region adjacent thereto.
It is preferable that the length L3 of the second portion 17 is larger than the length L2 of the first portion 16. The length L3 of the second portion 17 is preferably not less than 2.5 times, more preferably not less than 2.7 times, and preferably not greater than 3.2 times, more preferably not greater than 3.0 times the length L3 of the first portion 16. Thereby, it is possible to suppress the deformation of the land region adjacent to the second oblique segment 12.
The second portions 17 in this example are inclined with respect to the tire circumferential direction at an angle θ2 (not shown) lager than that of the first oblique segment 11. Preferably, the angle θ2 is 25 to 35 degrees. The edges of such second portion 17 can increase the frictional force in the tire circumferential direction, and it is possible to improve the traction performance on snowy/icy roads.
It is preferable that, as a result of the first and second oblique segments 11 and 12 configured as described above, the crown main groove 5 is provided with a first amplitude A1 of from 4.0% to 8.0% of the tread width TW. Such crown main groove 5 can improve the steering stability on dry roads and the traction performance on snowy/icy roads in a good balance.
If the amplitude of the crown main groove 5 is too large, there is a possibility that the steering stability on dry roads is deteriorated and the uneven wear occurs in the groove edges of the crown main groove 5. Therefore, a maximum amplitude (peak-to-peak amplitude) w1 measured from the axially innermost end to the axially outermost end of the crown main groove 5 is preferably not greater than 3.0 times, more preferably not greater than 2.5 times a maximum amplitude w2 of the crown main groove 5.
It is preferable that, as a result of the first and second portions 16 and 17 configured as described above, the second oblique segment 12 is provided with an amplitude A2 of not less than 0.30 times, more preferably not less than 0.45 times, and not greater than 0.75 times, more preferably not greater than 0.60 times the amplitude A1 of the zigzag configuration of the crown main groove 5. when running on snow-covered roads, such second oblique segment 12 can compress the snow in the groove more firmly than the first oblique segment 11 while suppressing excessive deformation of the adjacent land region thereto, therefore, it is possible to obtain a large shearing force from the compared snow block.
It is preferable that, as shown in
In this example, the angle θ3 of the axially inner groove sidewall 18 with respect to the tire radial direction is smaller than the angle θ4 of the axially outer groove sidewall 19 with respect to the tire radial direction. For example, the angle θ3 is preferably set in a range from 5 to 20 degrees, and the angle θ4 is preferably set in a range from 10 to 25 degrees. Thereby, the axially outer groove sidewall 19 becomes easier to deform relatively, therefore, it becomes easier to discharge the snow in the groove when running on snow-covered roads.
It is preferable that the shoulder main groove 6 has a zigzag periodical pattern having zigzag pitches smaller than those of the crown main groove 5 as shown in
The shoulder main groove 6 configured as such is increased in the length of the edges compared with a straight groove, therefore, it is possible to increase the scratch frictional force on snowy/icy roads.
By the above-described main grooves 3 (5, 6), the tread portion 2 is axially divided into a center land region 7, a pair of middle land regions 8 and a pair of shoulder land regions 9.
The center land region 7 is circumferentially divided into a plurality of center blocks 20 by center transverse grooves 21. The center transverse grooves 21 respectively extend from the first oblique segments 11 of one of the crown main grooves 5 to the respective opposite first oblique segments of the other crown main groove 5.
It is preferable that the center transverse grooves 21 are inclined to the opposite direction to the first oblique segments 11 inclined with respect to the tire circumferential direction. The center transverse grooves 21 configured as such can increase the frictional force in a different direction from the first oblique segments 11. This helps to improve the traction performance on snowy/icy roads in particular.
The center block 20 in this example comprises a pair of second block pieces 24 and a first block piece 23 therebetween, each inclined with respect to the tire axial direction. Preferably, the second block pieces 24 are each inclined to the opposite direction to the first block piece 23.
The center block 20 composed of such inclined block pieces 23 and 24 can deform moderately upon contacting with the ground. Thus, it is possible to suppress stuffing of snow in the crown main groove 5 when running on snow-covered roads.
The center block 20 in this example is provided with a plurality of center sipes 25. The center sipes 25 include
a first center sipe 26 one end of which is connected to one of the crown main grooves 5 and the other end of which is connected to the other crown main groove 5, and
a second center sipe 27 one end of which is connected to one of the crown main grooves 5 and the other end of which terminates within the block.
In this example, the first center sipe 26 is provided in the first block piece 23, and its one end is connected with the second oblique segment 12 of one of the crown main grooves 5 and the other end is connected with the second oblique segment 12 of the other crown main groove 5. The first center sipe 26 configured as such helps to increase the frictional force on snowy/icy roads. Moreover, the first center sipe 26 suppresses the deformation of the ground contacting surface of the first block piece 23 when running on dry roads, therefore, it is possible to suppress the uneven wear of the center block 20. The first center sipe 26 in this example is bent at two positions and composed of three straight segments which are two longer segments and a shorter segment therebetween.
It is preferable that the second center sipe 27 is bent at least partially in at least one position. The second center sipe 27 configured as such can maintain the apparent rigidity of the block when the opposing sidewalls of the sipe contact with each other, therefore, it is possible to maintain the steering stability on dry roads. The second center sipe 27 in this example is bent at a middle position, and composed of two straight segments.
The center block 20 in this example is preferably provided with a slot 28 at a recessed corner portion 22 between the edge of the first block piece 23 and the edge of the second block piece 24.
The slot 28 formed at such corner position 22 helps to compress the snow and discharge the compressed snow in cooperation with the deformation of the block when running on snow-covered roads. At this time, the snow in the slot 28 is combined with the snow in the crown main groove 5 and discharged together. Thereby, the slot 28 can help to discharge the snow in the crown main groove 5, and improve the on-snow performance.
The tie-bar 32 in this embodiment is preferably provided in the radially outer surface thereof with a groove bottom sipe 33 extending along the widthwise center line of the groove 31. The groove bottom sipe 33 can opens when the middle land region 8 contacts with the ground, therefore, it is possible to suppress the stuffing of snow in the crown main groove 5 and the middle transverse groove 31.
As shown in
a second middle block 37 whose axially inner edge is defined by the second oblique segment 12 of the crown main groove 5.
It is preferable that the first middle block 36 has a taper portion 38 tapered toward the crown main groove 5 as shown in
In order to increase the frictional force on snowy/icy roads, each of the middle blocks 30 is preferably provided with a plurality of middle sipes 40. The middle sipes 40 in this embodiment are first middle sipes 41 disposed in each first middle block 36, and second middle sipes 42 disposed in each second middle block 37.
The first middle sipes 41 of the first middle block 36 each comprise a first portion 43 inclined with respect to the tire axial direction, and
a pair of second portions 44 disposed on both sides of the first portion and extending along the tire axial direction.
The first middle sipes 41 configured as such can increase the frictional force on snowy/icy roads while maintaining the apparent rigidity of the first middle block 36.
The second middle sipes 42 of the second middle block 37 each comprise a first portion 43 inclined with respect to the tire axial direction, and a second portion 44 disposed only on the axially outside of the first portion 43 and extending along the tire axial direction. Thereby, the second middle block 37 and the first middle block 36 become easy to deform in a different manner from each other, therefore, it is possible to suppress the stuffing of snow in the vicinity of the tie-bar 32 of the middle transverse groove 31.
The shoulder land region 9 in this example is circumferentially divided into shoulder blocks 50 by shoulder transverse grooves 51 extending from the shoulder main groove 6 to the tread edge Te.
The shoulder transverse grooves 51 in this example each comprise an axially inner first groove portion 53 and an axially outer second groove portion 54.
The first groove portion 53 is preferably provided with a tie-bar 55 rising from the groove bottom and connecting between the blocks on the both sides thereof as with the middle transverse groove 31 (shown in
The second groove portion 54 has a larger width than the first groove portion 53. Thereby, the width of the shoulder transverse groove 51 increases stepwise toward the outside in the tire axial direction in order to improve the wandering performance on snowy/icy roads.
In order to further increase the above-described effects, the shoulder block 50 is preferably provided with a concaved portion 52 by cutting off a part of the block edge which defines a part of the tread edge Te so that the concaved portion 52 is connected to an axially outside part of the second groove portion 54.
Further, the shoulder blocks 50 are each provided with a shoulder narrow groove 57 connecting between a pair of the shoulder transverse grooves 51 adjacent in the tire circumferential direction. Thereby, the shoulder block 50 is axially subdivided into an axially inside block piece 58 and an axially outside block piece 59.
Furthermore, each of the shoulder blocks 50 is preferably provided with a shoulder sipe 60 intersecting with the shoulder narrow groove 57. The shoulder sipe 60 preferably has an axially inner end connected to the shoulder main groove 6 and an axially outer end terminating within the shoulder block 50. Further, it is preferable that the shoulder sipe 60 extends in a zigzag manner. In this embodiment, two shoulder sipes 60 are disposed in each shoulder block 50. The shoulder sipe 60 configured as such can increase the frictional force on snowy/icy roads while maintaining the apparent rigidity of the shoulder block 50.
While detailed description has been made of the pneumatic tire as an embodiment of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiment.
Pneumatic tires of size 275/55R20 were made by way of test based on the tread pattern shown in
The common specifications of the test tires and the test methods are as follows.
Rim: 20×9.0 J
Tire pressure: 250 kPa
Test car: displacement of 3700 cc, 4WD-car
Tire mounting position: all wheels
According to the ASTM F1805 test methods, frictional forces exerted on the test tires were measured while the test car was driven on snowy/icy roads at a constant speed of 8 km/h. The results are indicated in Table 1 by an index based on the frictional force of the comparative example being 100, wherein the larger the numeric value, the better the traction performance on snowy/icy roads is.
The steering stability was evaluated based on the driver's feeling while the test car was driven on a dry road surface of a test course.
The results are indicated in Table 1 by an evaluation point based on the comparative example being 100, wherein the larger the numeric value, the better the steering stability is.
From the test results, it was confirmed that the tires as the working examples exerted excellent running performance on snowy/icy roads while maintaining the steering stability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-009930 | Jan 2016 | JP | national |
