WO2014188324A1

WO2014188324A1 - Tyre tread band

Info

Publication number: WO2014188324A1
Application number: PCT/IB2014/061535
Authority: WO
Inventors: Marco Andrea MAGGI; Mattia GIUSTINIANO
Original assignee: Bridgestone Corporation
Priority date: 2013-05-23
Filing date: 2014-05-19
Publication date: 2014-11-27
Also published as: ITBO20130246A1

Abstract

A tread band (4) for a tyre (1), the tread band having a number of blocks (11), each having a leading edge (12) and a trailing edge (13), which extend transversely and are located at longitudinally opposite ends of the block (11), and respectively define, the part of the block (11) that first contacts the road surface, and the part of the block (11) that detaches last from the road surface; each block (11) has at least one cavity (14) oriented longitudinally and originating from a leading edge (12); and each block (11) also has two sipes (16), which are located at two sidewalls (15) of and transversely delimiting the cavity (14') and also and define an extension, inward of the block (11), of the longitudinal sidewalls (15) of the cavity (14).

Description

TYRE TREAD BAND

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to a tyre tread band.

PRIOR ART

When the tyre is subjected to braking on a wet road surface, the capability thereof of transmitting force to the underneath road surface can be limited by the interposition of water, typically rain, between the block and the surface itself; in this case, as there is no more direct contact between the tyre and the road surface, there is no more friction between the tyre and the road surface and therefore the transmitted braking force reduces considerably.

In the patent application WO2012053559A1 a tyre tread band is described allowing to reduce the interposition of water between the block and the road surface thanks to a particular shape of the blocks. In particular, each block has a series of cavities which are oriented longitudinally and originate from a leading edge or a trailing edge of the block. The presence of the cavities allows increasing the contact pressure between each block and the road surface and therefore it increases the capability of the block (in particular of the leading edge of the block) to break the water film covering the road surface to contact directly the road surface itself.

DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a tyre tread band allowing to increase the adherence on wet surface and, at the same time, can be implemented easily and economically. According to the present invention a tyre tread band is provided, according to what defined in the enclosed claims .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be now described with reference to the enclosed drawings, illustrating a not-limiting embodiment example thereof, wherein:

• figure 1 illustrates schematically a side section of a tyre portion equipped with a tread band implemented according to the present invention;

· figure 2 illustrates a schematic and plan view of a portion of the tyre tread band of figure 1;

• figure 3 illustrates a side and schematic view of the tyre of figure 1 highlighting a single tread band block impacting on the road surface;

· figure 4 illustrates a perspective and schematic view of a single tread band block of the figure 2; and

• figure 5 illustrates a longitudinal and schematic section of a block portion of figure 4.

PREFERRED EMBODIMENTS OF THE INVENTION

In figure 1, a tyre is designated as a whole with number 1 comprising a toroidal body ply 2, which has two annular beads 3 and supports a tread band 4 made of a vulcanized rubber-based material. Between the body ply 2 and the tread band 4 a tread belt 5 is interposed, which comprises two tread plies 6; each tread ply 6 consisting of a rubber tape wherein a number of (not illustrated) ropes is drowned, which are arranged side-by- side with a pre-established pitch and form a determined tilting angle with an equatorial plane of the tyre 1. Furthermore, the body ply 2 supports a pair of side walls 7 arranged between the tread band 4 and the beads 3.

The tread band 4 has a tread surface 8, delimiting outwardly the tread band 4 (i.e. it is arranged radially outside) and upon use it rests on the road surface. As it is better illustrated in figure 2, the tread surface 8 of the tread band 4 is crossed by a relief pattern defined by a plurality of longitudinal grooves 9 (or peripheral grooves 9) extending along the longitudinal direction X (transversal to an axis of rotation of the tyre 1) and therefore they extend along the periphery of the tyre 1 itself, and by a plurality of transversal grooves 10 extending along the transversal direction Y and therefore they extend parallelly to the axis of rotation of the tyre 1 and perpendicularly to the longitudinal grooves 9. The longitudinal grooves 9 and the transversal grooves 10 form five rows of longitudinal blocks 11 elevating radially from the tread band 4. Each block 11 has approximately a parallelepiped shape with rectangular or trapezoidal section and it is delimited by corresponding grooves 9 and 10.

According to what illustrated in figures 2, 3 and 4, each block 11 has a leading edge 12 and a trailing edge 13, which extend transversely (i.e. along the transversal direction Y), they are arranged at opposed longitudinal ends of the block 1 and, respectively, define the part of the block 11 that first contacts the road surface and the part of the block 11 that detaches last from the road surface (trailing edge 13) . In other words and as well illustrated in figure 3, the leading edge 12 is the first top portion of the block 11 which contacts the road surface whereas the trailing edge 13 is the last top portion of the block 11 which detaches from the road surface.

According to what illustrated in figure 2, each block 11 has a pair of cavities 14, each one thereof is oriented longitudinally and originates from the leading edge 12 of the block 11 (i.e. both cavities 14 originate from the leading edge 12); in each block 11, the two cavities 14 are arranged side-by- side and at a given distance apart. According to a preferred embodiment, each block 11 has at least a cavity 14 (generally each block 11 has a number of cavities 14 comprised between one and four depending upon its transversal extension) . According to not illustrated alternative embodiments, only one portion of the blocks 11 has the cavities 14.

According to a preferred embodiment, each block 11 has cavities 14 only at the inletting edge, i.e. in each block 11 the trailing edge 13 is without the cavities 14.

According to what well illustrated in figures 4 and 5, each cavity 14 is transversely delimitated by two longitudinal walls 15; in other words, each cavity 14 has two longitudinal walls 15 defining the opposite transversal ends (i.e. along the transversal direction Y) of the cavity 14.

According to a preferred embodiment, each cavity 14 is wedge-shaped having its largest dimension at the leading edge 12; consequently, the cavity 14 is triangular in shape in longitudinal section (well visible in figure 5) having its largest dimension at the leading edge 12 (i.e. each longitudinal wall 15 of a cavity 14 is shaped like a right-angled triangle having its largest dimension at the leading edge 12) . The wedgelike shape of the cavities 14 allows avoiding the discontinuity in the stiffness of the blocks 11 (i.e. the stiffness of the blocks 11 varies gradually and not in a step-like way) and then it allows eliminating localized (i.e. concentrated in limited area and therefore irregular) areas in the blocks 11 themselves. According to what well illustrated in figures 4 and 5, at a cavity 14 each block 11 further comprises two slits 16 which are oriented longitudinally (i.e. peripherally), they are arranged at the two longitudinal walls 15 of the cavity 14 delimiting transversely the cavity 14 and constitute an extension (both along the longitudinal direction X and towards the vertical direction Z) inwards of the block 11 of the longitudinal walls 15 of the cavity 14 itself. In other words, each slit 16 has a larger dimension than the dimension of the cavity 14, i.e. each slit 16 covers a larger area than the area covered by the cavity 14 (as well illustrated in figure 5) . According to a preferred embodiment, the area covered by each slit 16 is at least twice the area covered by the cavity 14.

According to a preferred embodiment, each slit 16 is rectangular in shape extending in the X-Z plane (i.e. the plane defined by the longitudinal direction X and by the vertical direction Z) from the edges of the corresponding longitudinal wall 15 of the cavity 14.

According to a preferred embodiment, each slit 16 is of practically zero width when the corresponding block 11 is undeformed (i.e. when the corresponding block 11 does not touch the road surface and therefore it is not deformed elastically by the forces transmitting between the tyre 1 and the road surface); in other words, the two longitudinal surfaces of each slit 16 are in mutual contact when the corresponding block 11 is undeformed. This result is obtained thanks to the fact that each slit 16 is implemented by means of a very thin sheet and therefore under undeformed conditions it is of practically transversal zero width.

According to a preferred embodiment, each slit 16 is of depth P (i.e. a dimension measured along the vertical direction Z) ranging between 5% and 40% of the depth of the main grooves 9 or 10 (i.e. of the deeper grooves 9 or 10 which usually are arranged in central position) . Practically, each slit 16 is of a depth P (i.e. a dimension measured along the vertical direction Z) ranging between 0.5 and 3.0 mm.

It is important observing that each slit 16 covers only a limited and surface portion of the corresponding block 11 and therefore it is of a lesser depth than the main grooves 9 or 10 (i.e. the deeper grooves 9 or 10 which usually are arranged in central position) ; in this way, the slits 16 do not weaken excessively the transversal stiffness of the blocks 11 and therefore not compromise the performances of the tyre 1 on dry road surface .

Thanks to the presence of the slits 16 it is possible increasing sensibly the transversal deformability of the leading edge 12 of each block 11 in particular near the cavities 14 such increase in the transversal deformability of the leading edge 12 of each block 11 allows increasing significantly the contact pressure between the block 11, if the same is subjected to a transversal stress, and the road surface and therefore increasing the capability of the block 11 (in particular of the leading edge 12 of the block 11) to break the water film covering the road surface to arrive in direct contact with the road surface itself. In other words, the leading edge 12 of each block 11 must be able to exert a very high pressure on the road surface to succeed in breaking the water film covering the road surface and then arriving in direct contact with the road surface itself; thanks to the presence of the slits 16 the transversal deformability of the leading edge 12 of each block 11 is increased and therefore the pressure exerted by the leading edge 12 on the road surface is increased.

In this respect, it is important observing that it is the leading edge of each block 11 which must break the water film covering the road surface, whereas the trailing edge 13 of each block 11 has no role in breaking the water film covering the road surface; consequently, the presence of the slits 14 and of the slits 16 only in the leading edge 12 of each block 11 is useful .

In order to produce the tread band 4 a vulcanization mould is used having a series of very thin sheets determining the formation of the slits 16.

Each cavity 14 extends longitudinally, i.e. along the longitudinal direction X. In the embodiment illustrated in the enclosed figure, each slit 14 is perfectly longitudinal (i.e. perfectly parallel to the longitudinal direction X) . In alternative not illustrated embodiments, at least a portion of the cavities 14 could be substantially longitudinal, i.e. slightly tilted with respect to the longitudinal direction X (for example by an angle ranging from 0° and 20°) .

The above-mentioned tread band 4 has several advantages.

First of all, the above-mentioned tread band 4 allows increasing sensibly the performances in braking on wet surfaces by reducing the possibility that the block 11 does not succeed in transmitting the force to the road surface due to the interposition of the water film. Experimental tests have shown that, all other parameters being equal, the presence of the slits 16 allows improving by 3-7% the performances on wet surface .

Furthermore, the slits 16 do not involve significant worsening of other performances of the tyre 1 (in particular of the performances upon driving along a curve) , since, being limited in depth P, the slits 16 do not involve a significant increase in the transversal deformability of the blocks 11 of the tread band 4. Experimental tests have shown that, all other parameters being equal, the presence of the slits 16 determines a worsening by 1-2% in the performances upon driving along a curve on wet surface; it is clear that such worsening is few indicative and however it is sensibly smaller than the corresponding improvement in the performances on wet surface.

At last, but not less important, the implementation of the slits 16 is extremely simple and cheap, as in order to implement the slits 16 it is sufficient inserting suitable sheets in the vulcanization mould.

Claims

1) A tread band (4) for a tyre (1);

the tread band (4) comprises a number of grooves (9, 10) defining a number of blocks (11);

each block (11) has a leading edge (12) and a trailing edge (13) , which extend Lransverseiy, are located at longitudinally opposite ends of the block (11) , and respectively define the part of one block (11) that first contacts the road surface, and the part of the block (11) that detaches last from the road surface; and

at least one block (11) has at least one cavity (14) oriented longitudinally and originating from, a leading edge (12) ;

the tread band (4) is characterized in that the block ill) with the cavity (14) also comprises two slits (16) , which are oriented longitudinally, are located at two longitudinal wails (15) of and transversely deflclng the cavity (14), and define an extension, inwards of the block (11) _f of the longitudinal walls (15) of the cavity (14) .

2} A oread band (4) as claimed in Claim. 1, wherein each slit (16) is of practically zero width when the block (11) is undeformed.

3) A. tread band (4) as claimed in Claim 1 or 2, wherein each slit (16) is of a depth (P) ranging between. 5% and 40% of the depth of the main grooves (9, 10} .

4) A tread band (4) as claimed in Claim 1, 2 or 3, wherein the area covered by each slit. (16) is at least twice the area covered by the cavity (14) .

5} A tread band. (A) as claimed in one of Claims 1 to

4, wherein each slit (16) is rectangular in shape, and extends in the X-3 plane, i.e. the plane defined by the longitudinal axis X and vertical axis 2, from the edges of the corresponding longitudinal wall (15) of the cavity (14) .

6} A tread, band (4) as claimed in one of Claims 1 to

5, wherein the block (11.) has at least two cavities {14} located a given distance apart and both originating from the leading edge (12) .

7) A tread band (4) as claimed in one of Claims I to

6, wherein the cavity {14) is wedge-shaped with its largest dimension at the leading edge (12) ,

8) A tread band (4) as claimed in one of Claims 1 to

7, wherein the cavity (14) is triangular in longitudinal section_f with its largest dimension at the leading edge {12} .

9} A tread band (4) as claimed in one of Claims I to

8, wherein each block ill) only has cavities (14) at the leading edge, i.e. the trailing edge (13) of each block (11) has no cavities (14) .

.10) A tread band {4} as claimed in one of Claims i to 9_f wherein, the cavity (14) extends 1ongitudinaIiy up to less than half of the block ill) .

11; A tread band (4) as claimed in one of Claims 1 to 10, wherein each block (115 has at least one cavity (14) ,

12} A tread band (4) for a tyre (1);

the tread band (4) comprises a nu ber of grooves {9, 10} defining a number of blocks (11);

each block {11} has a leading edge (12) and a trailing edge {13} , which extend transversely, are located at longitudinally opposite ends of the block (11) , and respectively define the part of the block (11) that first contacts the road surface, and the part of the block (11} that detaches last frorii the road surface; and

at least one block (11) has at least one cavity (14) oriented longitudinally and originating from a leading edge (12) ;

the tread band (4) is characterised in that the cavity {14} is wedge-shaped with, its largest dimension at the leading edge {12} , i.e. the cavity (14) is triangular in longitudinal section, wish its largest dimension at the leading edge (12),

13) A tread band (4) for a eyre (1);

the tread band {4} comprises a number of grooves (9, 10) defining a number of blocks {115; each block (II) has a leading edge (12) and a trailing edge (13), which extend, transversely, are located at longitudinally opposite ends of the block (1.1} , and respectively define the part of e block (11) that first contacts the road surface, arid the part of the block {11) that detaches last f om the road surface; and

at. least one block (11) has at least one cavity (14) oriented longitudinally and originating from a leading edge (12) ;

the tread band {4) is cha acter!zed in that each block (11) only has cavities il4) at the leading edge, i.e. the trailing edge (13) of each block (11) has no cavities (14) .