WO2008102048A1

WO2008102048A1 - Improved belt structure in automobile tires

Info

Publication number: WO2008102048A1
Application number: PCT/FI2007/000043
Authority: WO
Inventors: Jani Ojala; Kai Hauvala; Raimo Perkiö
Original assignee: Nokian Renkaat Oyj
Priority date: 2007-02-21
Filing date: 2007-02-21
Publication date: 2008-08-28
Also published as: DE112007003335T5

Abstract

A pneumatic radial automobile tire comprises a toroidal carcass (10) with a carcass ply (11) and a breaker belt (3), in which the breaker belt plies have a first number (N1) of several lengthwise reinforcement strings (7), and at least one band belt (4) comprising a continuous band (5), which is radially (R) on top of the breaker belt (3) and extends spirally in several turns (M), and has a second number (N2) of longitudinal, optionally twisted cords (9) which are substantially co-directional with the tire rotation plane (P). Said jointless band belt (4) comprises a single band (5), in which said cords are composed of wires (6) plaited together and/or twisted together. The lengthwise reinforcement strings in said breaker belt (3) are metal re- inforcement strings, and the longitudinal cords (9) of the band (5) in said band belt (4) are metal cords. The band (5) is wound on top of the breaker belt for such a number of turns (M) that the resulting band belt has a width (W4) which covers said entire breaker belt width (W3a, W3b) or has a width less than said breaker belt width by tolerances (T).

Description

Improved belt structure in automobile tires

The invention relates to a pneumatic radial automobile tire, comprising: a toroidal carcass including a carcass ply; a breaker belt consisting of at least one breaker belt ply disposed radially outside said carcass ply, said breaker belt plies having belt widths and said breaker belt plies comprising a first number of several lengthwise reinforcement strings; and at least one band belt, consisting of at least one continuous band disposed radially on top of the breaker belt and extending spirally in several turns, and comprising a second number of longitudinal, possibly twisted cords which are substantially co-directional with a rotation plane of the tire.

Publication GB-2 064 445 describes a radial tire for heavy-duty vehicles, which is provided with a tread-reinforcing breaker belt ply, consisting of not less than two plies comprising parallel metal wires which extend in various plies crosswise at angles, according to figures at angles in the order of 20° to 30°, relative to a circumferential direction of the tire, as well as of not less than two edge plies, each consisting of parallel reinforcement plies and being disposed on the lateral edges of the breaker belt ply, on the opposite sides of a mid-circumferential plane of the tire at a distance therefrom, such that the reinforcement plies extend parallel with the circumferential direction of the tire and leave in a mid-section of the breaker belt ply, between the internal side edges of the edge plies, a zone which has no reinforcement ply in the circumferential direction of the tire. Specifically, in this case, each edge ply has a modulus higher than 5000 daN/cm and each edge ply is made of a reinforcement ply which has a major initial strain. These lengthwise reinforcement plies in the edge plies of the tread are preferably parallel wires or the like of aromatic polyamide. The purpose is to increase durability of the tire and particularly to prevent the belt ply from becoming torn off, even with extremely high axial loads applied to tires in heavy-duty vehicles.

Publication EP-O 748 705, on the other hand, describes principally a tread profile for a car tire, which, at least over the axially outer section of a point P, has a radius of curvature RC which gradually decreases towards the exterior of the tire. These points P exist on either side of the tire's equator plane at an axial distance which is 20% of half of the tread's width, the jointless band belt satisfying the following equations: tm > 3PmχR/E and 0,5 < S 2,0. Wherein tm = the strength (kgf) of a cord made of organic fiber, Pm = the maximum pressure (kgf/cm²) of a tire, R = the radius (cm) of a jointless band belt in the tire's equator plane, E = the cord count of a jointless band belt per 1 cm width, S = the mean strain (%) of an organic fiber cord. It is further defined in this publication that the jointless band belt explicitly consists of at least one organic fiber, such as aramid fiber, said fibers in the band being embedded in rubber in a parallel relationship, and that this jointless band belt is obtained by winding the band for a continuous spiral between the tire carcass and the tire tread. In the most advantageous option according to the publication, the jointless band belt lies directly on top of the carcass ply. According to the publication, however, it is possible to design the belt so as to include other breaker plies as well, these traditional breaker belts being disposed on the outside of the carcass ply and radially inside the band belt. Consequently, these breaker belt plies consist of a conventional tire ply, in other words parallel and rubber-coated cords of organic fibers, for example the same fibers as the band belt. Thus, these breaker belts may be composed of aramid fiber, but can also be composed of nylon fiber, polyester fiber or rayon fiber. The purpose is to achieve an improved road contact in cornering. Hence, this more recent publication EP-O 748 705 totally abandons metal as a structural material for belts and teaches the use of organic fiber.

Patent publication US 5,558,144 discloses a pneumatic radial tire containing a non- metallic cord breaker belt disposed radially outside a carcass, and a jointless band belt disposed radially outside the breaker belt, said band belt being made of at least one hybrid cord wound spirally and continuously in the circumferential direc- tion of the tire at an angle of 0° to 3° with respect to the tire equator. This band belt comprises a pair of edge bands each covering each edge portion of the breaker belt and a main band disposed radially outside thereof covering the substantially full width of the breaker belt. Thus, the construction in fact comprises three band belts and the breaker belt edge areas have substantially more band belt turns, in which respect the construction complies with that of GB-2 064 445 as evident even by comparing the figures of these publications. The hybrid cord of US 5,558,144 comprises a low elastic modulus thread and a high elastic modulus thread which are finally-twisted together. The low elastic modulus thread comprises at least one low elastic modulus fiber having an elastic modulus of not more than 2000 kgf/cm² and first-twisted, and the high elastic modulus thread comprises at least one high elastic modulus fiber having an elastic modulus of not less than 3000 kgf/cm² and first-twisted. In the band belt ply, the count E for the hybrid cord per 5 cm width, the stress F1 in kgf of the hybrid cord at 2% elongation, and the stress F2 in kgf of the hybrid cord at 6% elongation satisfy the two following relationships: F1xE<60 and F2χE>160. In particular, the thickness in denier of the low elastic modulus thread is not more than half of the thickness in denier of the high elastic modulus thread, and the first-twist count of the low elastic modulus thread is not more than equal to the final-twist count. According to the publication, for the low elastic modulus fiber, nylon fiber, polyester fiber or the like can be used, and for the high elastic modulus fi- ber, aromatic polyamide fiber, polyvinyl alcohol fiber, carbon fiber, glass fiber or the like can be used. Thus, both the breaker belt and the band belt are made of a non- metallic material. An objective in the publication is to reduce the tire weight and at the same time to maintain handling and performance at high rates of speed. Hence, this more recent publication US 5,558,144, just like publication EP-O 748 705, totally abandons steel as a structural material for belts and, instead, teaches the use of polymer fibers.

What is special about the invention is that said radial tire comprises a jointless band belt consisting of a single band, whereby: the lengthwise reinforcement strings of at least one breaker belt ply in said breaker belt are metal reinforcement strings and the longitudinal cords of the band in said band belt are metal cords; and that said band is wound on top of the breaker belt for such a number of turns that the resulting band belt covers said entire breaker belt width. According to a particular embodiment of the invention, at least the metal cords of a band belt or jointless belt (JLB) are made of steel, so the invention can be referred to as "a steel JLB belt" structure. Here, the band belt comprises a band, which is coiled spirally on top of a tire breaker belt which in turn generally comprises 1-3 breaker belt plies in which the reinforcement strings are preferably also of steel, either in such a way that the coiling leaves gaps of a few millimeters between adjacent bands or in such a way that the winding/coiling even results in two plies of band or the result of coiling lies somewhere between these limit values.

An advantage of the invention is that a radial deformation caused by inertial force is very small, even at high speeds. In other words, the tire retains a constant contact area and shape regardless of speed. As a result, the tire retains its roadholding qualities even as the tire warms up and running speed increases. The tire is also improved in terms of its speed endurance.

The invention will now be described in detail with reference to the accompanying figures.

Fig. 1 shows generally a pneumatic radial automobile tire provided with a jointless band belt of the invention in the circumferential direction on top of a breaker belt, in a cross-section along the axis of tire rotation.

Fig. 2 shows in more detail a tire carcass structure and breaker belt, as well as a continuous, jointless band belt of the invention coiled in a similar view to that of fig. 1 , but in a larger scale and from a detail I in fig. 1. Figs. 3A-3B show two other methods of coiling for a continuous, jointless band belt of the invention, in a view similar to fig. 2. In figs. 3-3B the band belt has its band illustrated in principle, as it should be appreciated that, in reality, non-vulcanized rubber material and rubber material during the course of vulcanization have plastic- ity, leaving no gaps.

Figs. 4A-4C show two feasible methods of longitudinal twisting-together for continuously extending cords present in a jointless band belt, and respectively one feasible method of longitudinal plaiting-together, in a lateral view of the cord from a di- rection Il in figs. 2, 3A and 3B.

Fig. 5 shows the relationship between a stretching longitudinal force and a strain in a steel JLB of the invention and a nylon JLB of the prior art.

Fig. 6 shows the shape of a tire footprint achieved by a pneumatic radial automobile tire provided with a jointless band belt of the invention, even at high speeds and in cornering.

Figs. 7-8 visualize, on the one hand, a deformation in a pneumatic radial tire pro- vided with a jointless band belt of the invention, i.e. a steel JLB, and, on the other hand, a deformation in a pneumatic radial tire provided with a jointless band belt of the prior art, i.e. a nylon JLB, at a running speed of 300 km/h, in a view from the same direction as fig. 1. In the figures, an inner contour line in the tread region represents the tire at rest and an outer contour line represents the tire at a speed of 300 km/h, and in the tire side regions, an outer contour line represents the tire at rest and an inner contour represents the tire at a speed of 300 km/h.

Fig. 9 shows, based on deformations depicted in figs. 7 and 8, the relationship between a tire diameter and a running speed, on the one hand in a radial tire provided with a jointless band belt of the invention (steel JLB) and on the other hand in a radial tire provided with a jointless band belt of the prior art (nylon JLB).

Fig. 10 shows positions for lengthwise metal reinforcement strings in two breaker belt plies as viewed in an orthogonal direction, from a direction Il in fig. 2 and at the same time along a plane Ill-Ill in fig. 2.

The pneumatic radial automobile tire comprises, among other things, a toroidal carcass 10 including a carcass ply 11 , a breaker belt 3 consisting of at least one breaker belt ply 2a, 2b disposed radially R outside said carcass ply 11 , said breaker belt plies having belt widths W3a, W3b. Thus, the number of breaker belt plies can be one, two, three or more and the belt widths W3a, W3b thereof, whenever there are two or more breaker belt plies, can be equal to or slightly different from each other. The breaker belt plies 2a, 2b comprise a first number N1 of several lengthwise reinforcement strings 7, in this case reinforcement strings made of a metal, i.e. metal reinforcement strings 7, which are preferably made of steel, in other words steel reinforcement strings 7. These metal reinforcement strings 7 or steel reinforcement strings 7 establish angles K2a, K2b within the range of 10° to 30° relative to a plane of rotation P of the tire, and establish at the same time said angle with respect to the circumferential direction or toroidal form of the tire. The plane of rotation P comprises any plane which is perpendicular to the axis of rotation of a tire. In the event that the number of breaker belt plies is two or more, the metal/steel reinforcement strings 7 present in various plies are crosswise to each other, especially in such a way that the angles K2a and K2b open up in the way of a mirror image onto the opposite sides of the plane of rotation P, as perceivable from fig. 10. The metal/steel reinforcement strings 7 can be reinforcement strings plaited or twisted from filaments or non-twisted, generally similar to each other in each breaker belt ply, yet can also be dissimilar. The reinforcement strings can be made either by plaiting or twisting filaments directly together or the filaments can be first twisted or plaited for reinforcement prestrings, which are then twisted or plaited for the reinforcement strings 7. The rubber-material embedded reinforcement strings 7, establishing a breaker belt ply, extend usually once around the tire periphery, whereby the breaker belt plies are in a way provided with splices.

The pneumatic radial automobile tire further comprises a band belt 4 consisting of a continuous band 5 disposed radially R on top of the breaker belt 3 and extending spirally in several turns M, thus providing a jointless belt 4 (JLB). Hence, the band is wound or coiled on top of the breaker belt. This band 5 comprises a second number N2 of longitudinal cords 9 which are substantially co-directional with the plane of tire rotation P, thus being also substantially co-directional with the tire pe- riphery. In any case, the band belt's 4 cords are - if not absolutely parallel to the plane of rotation P - at an angle of no more than 5° and typically at an angle of no more than 2° with respect to the plane of tire rotation P. Because of its small size, this particular angle is not shown in the figures, but the band 5 and thereby its cords are in a more or less orthogonal position to the plane of the figures, the size of the actual angle being after all determined by a spirality of the former, i.e. by a pitch of turns φ. Accordingly, the direction of cords approaches that of the plane of rotation P. These cords 9 are embedded in a rubber material, which is not yet vulcanized during the tire assembly process and which has a band width W5, whereby a system of the rubber material and the cords establishes the discussed band 5. In the band 5 according to the invention, the above-mentioned second number N2 of cords 9 is not less than two and not more than fifteen.

According to the invention, the radial tire 1 includes a jointless band belt 4 consist- ing of just one band 5, wherein said cords 9 comprise wires 6 plaited together, as shown in fig. 4C, and/or wires 6 twisted together, as shown in figs. 4A and 4B. Further according to the invention, the material for cords 9 is a metal, preferably the material is steel, in other words the wires making up the cords 9 are made of metal, and typically of steel. The material of these metal cords 9 has an elastic modulus E of not less than 160 GPa and a shear modulus G of not less than 70 GPa regardless of a number of loading cycles for the cord and temperatures encountered within the tire belts 3, 4 during operation. Exactly the same way, the material of the above-mentioned metal reinforcement strings 7 has an elastic modulus E of not less than 160 GPa and a shear modulus G of not less than 70 GPa regardless of a number of loading cycles for the reinforcement cord and temperatures within the tire belts 3, 4. The metal/steel wires 6, which make up the above metal/steel cords 9, have a cross-sectional shape which can be a circle or other than a circle.

Each metal cord or steel cord 9 comprises not less than two and not more than nine metal wires or, respectively, steel wires 6. Thus, the cord of fig. 4C comprises three wires 6 plaited together to make up a steel cord 9, and the cord of fig. 4A includes two wires 6 twisted together to make up a steel cord 9. Another conceivable course of action is that some of the metal/steel wires 6 to be included in each metal/steel cord are either first-twisted around each other or fist-plaited with each other to make up strands or precords 19 and then these precords/strands are either twisted around each other or plaited with each other to make up said steel cords 9, as shown in the embodiment of fig. 4B by means of four wires 6. Specifically, according to the invention, the longitudinal cords 9 in the band 5 of the band belt 4 are made of metal, i.e. are metal cords 9, and preferably the cords are made of steel, i.e. are steel cords. This plaiting and/or twisting of wires and a proper choice of the metal material enable the fact that the longitudinal force-strain curve for the band has an initial strain portion with a first angular coefficient p1 and a functional strain portion with a second angular coefficient p2, said angular coefficients having a ratio p2/p1 which is at least 15 or at least 25 as the type of angular coefficient is N/%, in other words the longitudinal force in Newtons per strain in percentage. The initial portion is active during tire vulcanization and the initial portion has its upper limit defined whereat the wires have a strain of less than 1 %, in other words the initial portion lies in the strain range of 0% to 1 %. The truly effected strain depends e.g. on a vulcanization mold. Over the initial portion the angular coefficient p1 is less than 120 N/% or preferably less than 80 N/%, which low figure is at moment believed to result from the fact that the together-twisted or together-plaited wires of a cord at this stage tighten relative to each other with a result that just local deformations occur in the wires. The functional portion, in turn, is active when the tire is in service and mounted on an automobile, i.e. when the tire is used for driving, and the functional portion has its lower limit defined whereat the strands have a strain of more than 2%, in other words the functional portion lies in the strain range beyond 2%. Especially the functional portion having a high angular coefficient p2 of more than 600 N/%, or preferably more than 1000 N/%, or typically not less than 1800 N/%, ensures that tire deformations at high running speeds, with inertial forces striving to increase the tire diameter, are slight and the tire footprint remains optimal at high running speeds and in cornering. The high rate angular coefficient p2 over the functional portion is expected to result from the fact that at this stage the cord wires are subjected to a longitudinal force which strives to cause deformation across the entire cross-sectional area of the wires. In prior art solutions, wherein the jointless belt is made of some polyamide - in the figures this material is referred to by the word "nylon", which in this context is not in reference to any trademark - the angular coefficient has its value, irrespective of strain and possible twisting, in the order of 50...70 N/%, whereby the deformation during the course of running can be very significant indeed. In fig. 5, the values of N/% existing in a tire structure of the invention are demonstrated by the curve "Steel-JLB", and the values of N/% existing in a tire structure of the prior art by the curve "Nylon-JLB". Fig. 7 visualizes a very small change of radius ΔR1 caused by a structure of the invention in one exemplary tire, and fig. 8 shows a large change of radius ΔR2 caused by a prior known structure in a respective exemplary tire, the exemplary tire in both figures - 225/45R17 Nokian Z - thus being of the same type, the only difference regarding the material for the cords 9 of the band belt 4. More specifically, on the basis of fig. 9, which involves the same tires as figs. 7 and 8, the total diameter increase at the speed of 320 km/h is about 15 mm, i.e. ΔR1 is about 7.5 mm, which for the most part resets gradually - the increase being a result of several different factors such as inertial forces and warming - as the rotation comes to a halt. The presently discussed increases in diameter and radius are values obtained by tires put to this test for the first time - the increases in diameter and radius change a little as an already tested tire is tested again. With a prior art construction, the otherwise same type of tire shows a total diameter increase at 320 km/h of about 27 mm, i.e. ΔR2 is about 13,5 mm, which also resets gradually as the rotation comes to a halt. Accordingly, in a tire of the invention, the above total change ΔR1 of the outer radius R is proportionally, i.e. ΔR1/Rχ100%, not more than 3% or typically in the order of 2%...2,5%, when the driving speed is 320 km/h. It is also indicated in figs. 7 and 8 that the maximum tire width decreases as the radius and diameter increase, and in a tire of the invention the increase in width is smaller than in a prior art tire. On the other hand, fig. 6 shows that a tire of the invention - here also the same exemplary tire 225/45R17 Nokian Z according to the invention - produces at various speeds and in various driving conditions invariably an optimal shape footprint.

The band 5 of the invention has been wound on top of the breaker belt 3 for such a turn count M that the resulting band belt 4 has a width W4 which covers an entire breaker belt width W3a, W3b or a width which is less than the breaker belt width by a tolerance T, said tolerance T being not more than 10% of the breaker belt width W3a, W3b. Moreover, the band 5 of the invention is wound on top of the breaker belt 3 in such a way that the resulting band belt 4 has a constant mean thickness S across the band belt width W4. In other words, the band belt does not have substantial discontinuities, nor does it have in one embodiment at least any notable increased lateral thicknesses, as shown in fig. 1 , in which context it should be appreciated that gaps between the turns of band - fig. 2 shows very small gaps between the bands - are not regarded as discontinuities because, after all, the band does continue without disruptions even in those cases, nor is the overlapping between band turns - fig. 3A shows slight overlapping between the bands, while fig. 2 shows no overlapping and fig. 3B shows a band in two plies, hence no overlapping - regarded as discontinuities or increased lateral or other thickness. Normally, the maximum size of gaps between turns of band is not larger than a band width W5. In another embodiment, the band belt 4 may have increased lateral thicknesses 14, which in this case are produced by the same single band 5 as the rest of the joint- less band belt, the positions of said increased lateral thicknesses being presented by dashed reference lines in fig. 1. The increased lateral thicknesses can be made by a change from a non-overlapping band to an overlapping band, or from an overlapping band to a band in double or more layers.

Claims

1. A pneumatic radial automobile tire, comprising:

- a toroidal carcass (10) including a carcass ply (11); - a breaker belt (3) consisting of at least one breaker belt ply (2a, 2b) disposed radially (R) outside said carcass ply (11 ), said breaker belt plies having belt widths (W3a, W3b) and said breaker belt plies having a first number (N1 ) of several lengthwise reinforcement strings (7); and

- at least one band belt (4) comprising a continuous band (5), which is disposed radially (R) on top of the breaker belt (3) and extends spirally in several turns (M), and has a second number (N2) of longitudinal, optionally twisted cords (9) which are substantially co-directional with a tire rotation plane (P), characterized in that said radial tire (1) has a jointless band belt (4) comprising a single band (5), in which said cords are composed of wires (6) plaited together and/or twisted together, whereby:

- the lengthwise reinforcement strings of the at least one breaker belt ply (2a and/or 2b) in said breaker belt (3) are metal reinforcement strings, and the longitudinal cords (9) of the band (5) in said band belt (4) are metal cords; and

- said band (5) is wound on top of the breaker belt (3) for such a number of turns (M) that the resulting band belt (4) has a width (W4) which covers said entire breaker belt width (W3a, W3b) or has a width less than said breaker belt width by tolerances (T).

2. A pneumatic radial automobile tire as set forth in claim 1 , characterized in that the metal reinforcement strings (7) of said at least one breaker belt ply (2a, 2b) form angles (K2a, K2b) between 10° and 30° relative to the tire rotation plane (P); and that said lengthwise metal reinforcement strings (7) are plaited or twisted or non-twisted reinforcement strings.

3. A pneumatic radial automobile tire as set forth in claim 1 or 2, characterized in that said metal reinforcement strings (7) and metal cords (9) both have Elastic Modulus at the minimum 160 GPa and Shear Modulus at the minimum 70 GPa irrespective of a number of loading cycles for the reinforcement string or the cord and temperatures encountered within the tire belts during operation.

4. A pneumatic radial automobile tire as set forth in claim 3, characterized in that said lengthwise metal reinforcement strings (7) and said longitudinal metal cords (9) are made of steel.

5. A pneumatic radial automobile tire as set forth in claim 3 or 4, characterized in that the second number (N2) of the metal/steel cords in the band belt's band (5) is at the minimum two; and that said second number (N2) of the metal/steel cords (9) is at the most fifteen.

6. A pneumatic radial automobile tire as set forth in claim 3 or 4 or 5, characterized in that each of said metal/steel cords (9) comprises at minimum two and at most nine metal/steel wires (6).

7. A pneumatic radial automobile tire as set forth in any of claims 3-6, characterized in that in the band (5) of said band belt:

- the metal/steel wires (6) are either twisted around each other or plaited with each other to establish said metal/steel cords (9); and - some of the metal/steel wires (6) for each metal/steel cord are at first either twisted around each other or plaited with each other to establish precords (19), and said precords are then either twisted around each other or plaited with each other to establish said metal/steel cords (9).

8. A pneumatic radial automobile tire as set forth in any of claims 3-7, characterized in that the metal/steel wires (6) establishing said metal/steel cords (9) have a cross-sectional shape which is a circle or deviates from a circle.

9. A pneumatic radial automobile tire as set forth in any of the preceding claims, characterized in that said metal/steel cords (9) in the band belt's band (5) are plaited and/or twisted, such that the longitudinal force-strain curve for the band has an initial strain portion of less than 1% with a first angular coefficient (p1) and a functional strain portion of more than 2% with a second angular coefficient (p2), said angular coefficients having a ratio (p2/p1 ) which is not less than 15 or not less than 25 as the characteristic of angular coefficient is N/%.

10. A pneumatic radial automobile tire as set forth in any of the preceding claims, characterized in that said single band (5) is wound on top of the breaker belt (3), such that: - the resulting band belt (4) extends in a constant mean thickness (S) over said band belt width (W4), or

- results in increased lateral thicknesses (14) on those sides of the band belt (4), which face away from each other and are parallel to the tire shoulders.

11. A pneumatic radial automobile tire as set forth in any of the preceding claims, characterized in that there is a gap or there is no gap between the spirally extending turns (M) of said single band (5) or the spirally extending turns (M) are overlapping.

12. A pneumatic radial automobile tire as set forth in any of the preceding claims, characterized in that the outer tire radius (R) has a total proportional change (ΔR1 ) which is not more than 3% at the driving speed of 320 km/h.