Run-flat tyre

0001The present invention relates to a pneumatic tyre, more particularly to a run-flat tyre having an improved sidewall reinforcing structure.

0002In order to improve run-flat performance such as the run-flat distance of a pneumatic tyre, as shown in Fig.4, a tyre which has a sidewall portion (s) reinforced with a relatively thick rubber layer (g) has been proposed, wherein this thick rubber layer (g) is disposed on the axially inside of the carcass to extend along the inside of the tyre.

0003In this reinforcing structure, however, under run-flat conditions, damage starting from the carcass ply turnup edge (f1) is liable to occur as the edge (f1) is positioned in the sidewall portion, especially when it is positioned around the maximum tyre section width point. Further, the rubber layer (g) has a maximum thickness at the maximum tyre section width point. Under flat conditions, however, bending deformation becomes larger in the tyre shoulder portion than the maximum tyre section width portion. In other words, the bending deformation is concentrated in the shoulder portion. Thus, in this structure, the tyre has a tendency to have a weak point in the shoulder portion.

0004Such drawbacks may be eliminated by for example covering the edge (f1) with an additional carcass ply and increasing the thickness of the rubber layer (g). However, other problems arise such as an increase in the tyre weight and deterioration of ride comfort and dynamic performance under normal conditions.

0005GB-A-2 087 805 discloses a pneumatic safety tyre having a carcass comprising an inner and outer ply each of organic fibre cords and having turned-up portions from inside to the outside of the tyre and sidewall reinforcing rubber layers including an inside layer axially inside the main portion of the inner ply, a middle layer between the main portion of the inner ply and the main portion of the outer ply and an outside layer outside the main portion of the outer ply. At least one of the sidewall reinforcing rubber layers having a radially outer end located beneath the belt and at least one of the sidewall rubber layers having a radially inner end located radially outward of the bead core but inwards of the maximum tyre section width point, at the maximum tyre section width print, the total of the thickness of the inside layer, the thickness of the middle layer , and the thickness of the outside layer being not less than 0.5 times the thickness of the sidewall portion.

0006Another proposal in US 3 994 329 provides a safety tyre having bulbous sidewall rubber inserts and turn-up portions of an inner ply having their radially outer ends between the belt and the carcass.

0007EP-A-0 924 867 which was published on 12.06.2002 also proposes sidewall inserts between carcass plies which may have turn-ups extending to edges between the belt and the carcass main portion.

0008It is therefore, an object of the present invention to provide a run-flat tyre improved in run-flat performance, e.g. running distance, durability and the like without increasing the tyre weight and deteriorating running performance under normal conditions by means of improving the shoulder portions of the tyre.

0009Accordingly the present invention is a run-flat tyre as set out in claim 1.

0010Further aspect of the invention are set out in the sub-claims.

0011An embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings: <ul id="ul0001" list-style="none" compact="compact"><li>Fig.1 is a cross sectional view of an embodiment of the present invention;</li><li>Fig.2 is an enlarged cross sectional view of a shoulder portion thereof;</li><li>Fig.3 shows cross sections of the tyre under a normal condition and a flat condition obtained by a CT scanner; and</li><li>Fig.4 is a cross sectional view of a prior art tyre.</li></ul>

0012In the drawings, the run-flat tyre 1 according to the present invention comprises a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each with a bead core 5 therein, a radial ply carcass 6, a belt 7, 10 disposed radially outside the carcass 6 in the tread portion 2, and sidewall reinforcing layers 9 disposed in each of the sidewall portions 3.

0013In Fig.1, the tyre 1 is mounted on its standard wheel rim J and inflated to standard inner pressure but loaded with no tyre load. The sizes or dimensions of the tyre are measured under this condition if not specifically mentioned. Here, the standard 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 "Tyre 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. In case of passenger car tyres, however, as the standard pressure, 180 kPa is used.

0014The carcass 6 comprises an inner ply 6A and an outer ply 6B each made of organic fibre cords. For the organic fibre cords, rayon cords are used in this embodiment, but other materials such as polyester, nylon and the like can be used. The cords of each carcass ply are arranged radially at an angle of 75 to 90 degrees with respect to the tyre equator C so that the ply has a radial structure. In this embodiment, the cord angle in each ply is the same value of about 88 degrees but the inclining directions are opposite with respect to the tyre equator C. Thus, the cords of one ply cross those of the other ply at a small angle of about 4 degrees in this example.

0015The belt includes a breaker 7 and a band or bandage 10 disposed radially outside the breaker 7.

0016The breaker 7 comprises two crossed plies 7A and 7B, each ply made of parallel cords laid at an angle of from 10 to 35 degrees with respect to the tyre equator C. In this embodiment, each ply is made of aramid cords laid at 22 degrees. Aside from aramid cords, steel cords and the like can be used.

0017The band 10 is made of an organic fibre cord laid substantially parallel to the tyre circumferential direction. The band cords have a lower elastic modulus than the breaker cords.

0018In this embodiment, the band 10 is composed of a pair of axially spaced edge-band plies 10A covering the axial edges of the breaker 7 and a full-width band ply 10B disposed radially outside thereof and extending across the substantially full width of the breaker 7.

0019Preferably, each edge-band ply 10A has a width of about 10 to 20 % (in this example about 16%) of the axial width 3W of the breaker 7.

0020Both the band plies 10A and 10B in this embodiment are formed by spirally winding a tape of rubber, in which parallel nylon cords are embedded along the length thereof.

0021By using such a spiral band 10, it becomes possible to effectively prevent ply separation failure even if the tread portion 2 warps as shown in Fig.3 by a chain line. Thus, the durability under run-flat condition can be improved.

0022According to the present invention, the above-mentioned carcass plies 6A and 6B extend between the bead portions through the tread portion and sidewall portions and are turned up around the bead core 5 in each bead portion from the inside to the outside of the tyre so that: the carcass ply 6A comprises a pair of turnup portions 6b1 and a main portion 6a1 therebetween; and the carcass ply 6B comprises a pair of turnup portions 6b2 and a main portion 6a2 therebetween.

0023The edges 6e of the turnup portions 6b1 of the inner ply 6A extend to between the carcass 6 and breaker 7, and the overlap 11 of the turnup portion 6b1 with the breaker 7 has an axial length L of from 3 to 8 % (in this embodiment about 6.5%) of the axial width BW of the breaker.

0024The turnup portion 6b2 of the outer ply 6B has a height of about 0.4 to 0.6 times the tyre section height H (in this embodiment about 0.46 times) each from the bead base line BL. This means that the turnup end is positioned around the maximum tyre section width point M.

0025Incidentally, the tyre section height H is the radial height measured from the bead base line BL to the radially outermost point. The bead base line is an axial line passing to a position corresponding to the rim diameter.

0026In each of the above-mentioned bead portions 4, a bead apex 12 is disposed between the turnup portion 6b2 and main portion 6a2 of the outer carcass ply 6B. The bead apex 12 is made of a hard rubber and extends and tapers radially outwardly from the outside 5a of the bead core 5.

0027The above-mentioned sidewall reinforcing layers 9 include: an inside reinforcing rubber layer 9a disposed between the main portion 6a1 of the inner ply 6A and an air tight inner liner (i) disposed along the inside of the tyre; a middle reinforcing rubber layer 9b disposed between the main portions 6a1 and 6a2 of the inner and outer plies 6A and 6B; and an outside reinforcing rubber layer 9c disposed between the main portion 6a2 of the outer ply 6B and the turnup portions 6b1 and 6b2. Each of the reinforcing rubber layers 9a-9c tapers radially inwardly and radially outwardly.

0028In this embodiment, each layer (9a, 9b, 9c) has a radially outer end (9a1, 9b1, 9c1) located beneath, i.e. radially inwards of, the breaker 7 as shown in Fig.2, and a radially inner end (9a2, 9b2, 9c2) located radically inside the maximum tyre section width point M but radially outside the outer end 5a of the bead core 5.

0029The outer ends 9a1, 9b1 and 9c1 are placed at different axial positions so that the total thickness of the layers gradually changes from the tread portion 2 to the sidewall portion 3. In this embodiment, the outer end 9a1 is inmost, and the outer end 9c1 is outmost. Thus, the outer end 9b1 is in the middle of the others.

0030At least one of the radially inner ends 9a2, 9b2 and 9c2 of the reinforcing rubber layers 9a, 9b and 9c is positioned radially inwards of the maximum tyre section width point M. None of the radially inner ends 9a2, 9b2 and 9c2 is positioned radially inwards of the outer end 5a of the bead core 5.

0031In this embodiment shown in Fig.1, the radially inner tapered portion of the outside layer 9c and the radially outer tapered portion of the bead apex 12 are spliced, and in this spliced portion, the outside layer 9c is positioned axially outside the bead apex 12 and the radially inner end 9c2 thereof reaches near the radially outside of the bead core 5.

0032On the other hand, the radially inner ends 9b2 and 9a2 of the middle and inside layers 9b and 9a reach to radially different positions which are radially inwards of the radially outer end of the bead apex 12 but radially outwards of the radially out end 5a of the bead core 5.

0033As shown in Fig.2, the total thickness of the sidewall portion 3 is such that the total thickness S2 at a point B is set in the range of from 1.0 to 1.4 times, preferably more than 1.0 times but not more than 1.4 times, more preferably more than 1.0 times but not more than 1.2 times, still more preferably 1.1 to 1.2 times the total thickness S1 at the maximum tyre section width point M.

0034The point B is a point on the outer surface of the tyre at a radial height of 75 % of the tyre section height H. The total thickness S1, S2 is measured along the normal direction to the outer surface or profile of the tyre.

0035At the maximum tyre section width point M, the total (a1+b1+c1) of the thicknesses a1, b1 and c1 of the layers 9a, 9b and 9c, respectively, is set to be not less than 50 %, preferably 50 to 70 %, more preferably 50 to 65 %, still more preferably 55 to 65 % of the total thickness S1.

0036Further, at the above-mentioned point B, the total (a2+b2+c2) of the thicknesses a2, b2 and c2 of the layers 9a, 9b and 9c, respectively, is set to be not less than 40 %, preferably 45 to 60 % of the total thickness S2.

0037Preferably, the total (a2+b2+c2) is smaller than the total (a1+b1+c1).

0038At the maximum tyre section width point M, it is preferable that the layers 9a, 9b and 9c are substantially the same thickness (a1=b1=c1). But, the following relationships may be possible: a1<b1<c1 ; a1>b1>c1 ; a1>b1<c1 ; a1<b1>c1.

0039Each of the reinforcing rubber layers 9 is made of a rubber compound of low-heat-generation having a complex elastic modulus E* of from 7.0 to 12.0 MPa and a loss tangent (tan δ) of not more than 0.02, preferably not more than 0.01, more preferably in the range of from 0.008 to 0.001.

0040In this embodiment, all the layers 9a, 9b and 9c are made of the same rubber compound, but it is also possible to use different rubber compounds which satisfy <ul id="ul0002" list-style="none" compact="compact"><li>E*a>E*b>E*c or</li><li>E*a<E*b<E*c or</li><li>E*a<E*b>E*c or</li><li>E*a>E*b<E*c,</li></ul> wherein E*a, E*b and E*c are the complex elastic moduli of the layers 9a, 9b and 9c, respectively.

0041If the complex elastic modulus E* is outside the range of from 7.0 to 12.0 MPa, the bending rigidity of the sidewall portion 3 tends to decrease and heat generation increases and ride comfort deteriorates.

0042If the loss tangent (tan δ) is more than 0.02, heat generation increases and the sidewall is liable to be broken by built-up heat.

0043The results are indicated by an index based on the Prior Art tyre being 100. The larger the index, the longer the runable distance.

0044From the test results, it was confirmed that the Example tyres were remarkably increased in runable distance although the tyre weight was maintained at the same level as the Prior Art tyre.

0045Fig.3 shows cross-sections of the Embodiment tyre when loaded with 4.41 kN under normally inflated condition (solid line) and a flat condition (chain line). This shows that even when the tyre is punctured the Embodiment tyre can endure its load without parts of the inner surfaces touching. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="7" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" rowsep="0" align="left">Tyre</entry><entry namest="col2" nameend="col2" align="center">Prior</entry><entry namest="col3" nameend="col3" align="center">Ex.1</entry><entry namest="col4" nameend="col4" align="center">Ex.2</entry><entry namest="col5" nameend="col5" align="center">Ref.</entry><entry namest="col6" nameend="col6" align="center">Ex.3</entry><entry namest="col7" nameend="col7" align="center">Ex.4</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">Fig.4</entry><entry namest="col3" nameend="col3" align="center">Fig.1</entry><entry namest="col4" nameend="col4" align="center">Fig.1</entry><entry namest="col5" nameend="col5" align="center">Fig.1</entry><entry namest="col6" nameend="col6" align="center">Fig.1</entry><entry namest="col7" nameend="col7" align="center">Fig.1</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Carcass cord</entry><entry namest="col2" nameend="col7" align="center">rayon 1840 dtex/2</entry></row><row><entry namest="col1" nameend="col1" align="left">Breaker cord</entry><entry namest="col2" nameend="col7" align="center">aramid 1670 dtex/2</entry></row><row><entry namest="col1" nameend="col1" align="left">Band cord</entry><entry namest="col2" nameend="col7" align="center">nylon 1400 dtex/2</entry></row><row><entry namest="col1" nameend="col1" align="left">Reinforcing rubber layers</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col7" /></row><row><entry namest="col1" nameend="col1" align="left">Complex elastic modulus</entry><entry namest="col2" nameend="col2" align="center">9.2 MPa</entry><entry namest="col3" nameend="col7" align="center">inside=middle=outside= 9.2 MPa</entry></row><row><entry namest="col1" nameend="col1" align="left">Loss tangent</entry><entry namest="col2" nameend="col2" align="center">0.005</entry><entry namest="col3" nameend="col7" align="center">inside=middle=outside= 0.005</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">S1   (mm)</entry><entry namest="col2" nameend="col2" align="center">20</entry><entry namest="col3" nameend="col3" align="center">18</entry><entry namest="col4" nameend="col4" align="center">18</entry><entry namest="col5" nameend="col5" align="center">15</entry><entry namest="col6" nameend="col6" align="center">18</entry><entry namest="col7" nameend="col7" align="center">18</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">a1+b1+c1   (mm)</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">10</entry><entry namest="col4" nameend="col4" align="center">10</entry><entry namest="col5" nameend="col5" align="center">7</entry><entry namest="col6" nameend="col6" align="center">10</entry><entry namest="col7" nameend="col7" align="center">10</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">(a1+b1+c1)/S1</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">0.56</entry><entry namest="col4" nameend="col4" align="center">0.56</entry><entry namest="col5" nameend="col5" align="center">0.46</entry><entry namest="col6" nameend="col6" align="center">0.56</entry><entry namest="col7" nameend="col7" align="center">0.56</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">S2   (mm)</entry><entry namest="col2" nameend="col2" align="center">18</entry><entry namest="col3" nameend="col3" align="center">20</entry><entry namest="col4" nameend="col4" align="center">17</entry><entry namest="col5" nameend="col5" align="center">17</entry><entry namest="col6" nameend="col6" align="center">20</entry><entry namest="col7" nameend="col7" align="center">24</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">a2+b2+c2   (mm)</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">9</entry><entry namest="col4" nameend="col4" align="center">7</entry><entry namest="col5" nameend="col5" align="center">7</entry><entry namest="col6" nameend="col6" align="center">7</entry><entry namest="col7" nameend="col7" align="center">12</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">(a2+b2+c2)/S2</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">0.45</entry><entry namest="col4" nameend="col4" align="center">0.41</entry><entry namest="col5" nameend="col5" align="center">041</entry><entry namest="col6" nameend="col6" align="center">0.35</entry><entry namest="col7" nameend="col7" align="center">0.5</entry></row><row><entry namest="col1" nameend="col1" align="left">S2/S1</entry><entry namest="col2" nameend="col2" align="center">0.9</entry><entry namest="col3" nameend="col3" align="center">1.11</entry><entry namest="col4" nameend="col4" align="center">0.94</entry><entry namest="col5" nameend="col5" align="center">1.13</entry><entry namest="col6" nameend="col6" align="center">1.11</entry><entry namest="col7" nameend="col7" align="center">1.33</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">Run-flat performance</entry><entry namest="col2" nameend="col2" align="center">100</entry><entry namest="col3" nameend="col3" align="center">300</entry><entry namest="col4" nameend="col4" align="center">100</entry><entry namest="col5" nameend="col5" align="center">50</entry><entry namest="col6" nameend="col6" align="center">150</entry><entry namest="col7" nameend="col7" align="center">400</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Tyre weight</entry><entry namest="col2" nameend="col2" align="center">100</entry><entry namest="col3" nameend="col3" align="center">100</entry><entry namest="col4" nameend="col4" align="center">95</entry><entry namest="col5" nameend="col5" align="center">80</entry><entry namest="col6" nameend="col6" align="center">100</entry><entry namest="col7" nameend="col7" align="center">110</entry></row></tbody></tgroup></table></tables>