CA1209022A - Heavy duty low-section pneumatic radial tire and a process for manufacturing the same - Google Patents
Heavy duty low-section pneumatic radial tire and a process for manufacturing the sameInfo
- Publication number
- CA1209022A CA1209022A CA000457082A CA457082A CA1209022A CA 1209022 A CA1209022 A CA 1209022A CA 000457082 A CA000457082 A CA 000457082A CA 457082 A CA457082 A CA 457082A CA 1209022 A CA1209022 A CA 1209022A
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- belt
- cords
- tire
- belt layer
- carcass
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Abstract
BRIDGESTONE-57-230,059 Abstract of the Disclosure A heavy duty low-section pneumatic radial tire and a process for manufacturing the same are disclosed. This tire comprises a radial carcass toroidally extending between bead portions, a belt composed of a first and second belt layers successively superimposed around a crown portion of the carcass and a tread rubber having substantially the same width as the maximum width of the belt. In the belt, the first belt layer is composed of at least two cord plies each containing cords inclined at a small angle with respect to the equatorial plane of the tire, the cords of which being crossed with each other with respect to the equatorial plane, while the second belt layer is composed of at least one cord ply containing non-expansible or hardly expansible cords arranged in substantially parallel to the equatorial plane and extends over both sides of the first belt layer between the first belt layer and the carcass.
Description
Th-is invention relates to a heavy duty low-section pnewmatic radial tire and a process for manufacturing the same.
In general~ the heavy duty pneumatic radi.al 05 tire comprises a radial carcass toroidally extending over a pair of annular bead portions, a belt consisting of p]ural ply layers successively superimposed one upon the other about a crown portion of the carcass, and a tread rubber. As the radial carcass, there is 0 employed a single ply or plural plies using a strand cord of steel wire (hereinafter referred to as "steel cord"), or a cord of nylon fiber, polyester fiber, aromatic polyamide fiber [hereinafter referred to as Kevlar (trade name)] or the like. As to the belt, there are several cases~ one of which is a case that a first layer composed of an even number of cord plies, usually two cord plies each containing steel cords inclined at a small angle with respect to the equatorial plane of the tire, cords of which plies being crossed with each other, is combined with a second layer of a cord ply containing steel cords inclined at a. slightly larger angle with respect to the equatorial plane of the tire disposed between the first layer ancl the crown portion o~ the carcass. In another case, the first layer is directly superimposed about the crown porLion of the carcass and one or several of relatively e~pansible cords such as nylon cords are spirally wound around the first layer in substantially parallel to the equatorial ?~
plane o~ the tire and between the first layer and the tread rubber, or a tire cord fabric of nylon cords having the same spiral inclination angle as described above is piled onto the first layer.
05 Such a belt structure is suitably applied to the conventional tires having an aspect ratio of about l.O.
But, if it is intended to apply the above belt structure to heavy duty low-section pneumatic radial tires having an aspect ratio of not more than 0.8, particularly 0 about 0.4, the rigidity of the belt remarkably lowers at the both sides, so that the expected tread shape cannot be ensured.
That is, since the tire of this type is usually inflated at a high internal pressure of about 8 kg/cm2, the tenacity-bearing of the belt having a transversally spread shape becomes larger at its both sides than at the central portion. Consequently, the tread is transformed into a concave shape, whose footprint is a gourd shape having an axis in the
In general~ the heavy duty pneumatic radi.al 05 tire comprises a radial carcass toroidally extending over a pair of annular bead portions, a belt consisting of p]ural ply layers successively superimposed one upon the other about a crown portion of the carcass, and a tread rubber. As the radial carcass, there is 0 employed a single ply or plural plies using a strand cord of steel wire (hereinafter referred to as "steel cord"), or a cord of nylon fiber, polyester fiber, aromatic polyamide fiber [hereinafter referred to as Kevlar (trade name)] or the like. As to the belt, there are several cases~ one of which is a case that a first layer composed of an even number of cord plies, usually two cord plies each containing steel cords inclined at a small angle with respect to the equatorial plane of the tire, cords of which plies being crossed with each other, is combined with a second layer of a cord ply containing steel cords inclined at a. slightly larger angle with respect to the equatorial plane of the tire disposed between the first layer ancl the crown portion o~ the carcass. In another case, the first layer is directly superimposed about the crown porLion of the carcass and one or several of relatively e~pansible cords such as nylon cords are spirally wound around the first layer in substantially parallel to the equatorial ?~
plane o~ the tire and between the first layer and the tread rubber, or a tire cord fabric of nylon cords having the same spiral inclination angle as described above is piled onto the first layer.
05 Such a belt structure is suitably applied to the conventional tires having an aspect ratio of about l.O.
But, if it is intended to apply the above belt structure to heavy duty low-section pneumatic radial tires having an aspect ratio of not more than 0.8, particularly 0 about 0.4, the rigidity of the belt remarkably lowers at the both sides, so that the expected tread shape cannot be ensured.
That is, since the tire of this type is usually inflated at a high internal pressure of about 8 kg/cm2, the tenacity-bearing of the belt having a transversally spread shape becomes larger at its both sides than at the central portion. Consequently, the tread is transformed into a concave shape, whose footprint is a gourd shape having an axis in the
2~ widthwise direction of the tread, so that the uneven wear is apt to be caused and the wet skid resistance lowers disadvantageously.
It is, therefore, an object of the invention to effectively solve the problems inherent to the conventional heavy duty low-section pneumatic radial tire and to provide an advantageous process for manufacturing a heavy duty low-section pneumatic radial tire of this type without suffering the disadvantages ..;.
~Z~a. ~Z ~7 inherent to the conventional tire as clescribed above.
According to the invention, there is the provision of a heavy duty low-section pneumatic radial tire comprising a radia]. carcass toroidally extending 05 be-tween a pair of annular bead portions, a belt composed of plura] ply layers successively superimposed one upon the other around a crown portion of the carcass, and a tread rubber having substantially the same width as the maximum width of the belt; said belt being a combina-1o tion of a first belt layer with a second belt layer, said first belt layer being composed of at least two cord plies each containing cords inclined at a small angle with respect to the equatorial plane of the tire, the cords of which plies being crossed with each other with respect to the equatorial plane, said second beltlayer being composed of at leas-t one cord ply containing non-expansible or hardly expansible cords arranged in substantially parallel to the equatorial plane and extending over both sides of the first belt layer between the carcass and the first belt layer.
In the preferred embodiments of the invention, the radial carcass is composed of a si.ngle to several plies of the fiber cords each macle of nylon E:iber, polyester fiber o:r preferably Kevlar .tiber, or of a single or two plies at the most of the steel cords.
Further, the first belt layer uses the above fiber cords or steel cords arranged at an inclination angle of lO-~0 with respect to the equatorial plane of the l~z~
tire, while the second belt layer uses cords having a modulus of elast:icity of not less than 30X104 kg/cm2 and extends over a width wider -than that of the first belt layer and at substantially the same width as that 05 of the tread rubber. ~nd also, the second belt layer is arranged on the carcass such that at least 50%, preferably 60-80% of the second belt layer at its central portion is located along the cord pass line at the crown portion of the carcass, while the remaining o both side portions of the second belt layer are disposed on cushion rubbers each located at the shoulder portion of the carcass. Moreover, the second belt layer has a bearing ratio on resistance to tensile load of 60-90%
of the sum of the resistances to tensile load of the first and second belt layers per unit width calculated by the following formula:
T Ncos~2/Rm P
, wherein T is a tenacity of a cord, N is an end count of cords per unit width as measured at right angle to the cord, ~ is an inclination angle of the cord with respect to the equator:i.al plane of the tire, ~m is a radi~ls of each cord ply being a d:istance between the cord center and the tire center and P is a normal i.nternal pressure of the tire. ~n the tire according to the invention, it is preferable that the aspect ratio H/W is within a range of 0.9 o.i~, preferably ~ 2~ 2 ~
0.7-0.~ and the carcass flatness Rl/W' is within a range o:E 3-10, preferably 5-lO.
The heavy duLy low-section pneuma-tic radial tire according to the invention may advantageowsly be 05 manufactured by a process comprising the steps of:
forming a first green case in which a ply(s) for carcass is placed on an outer circumference of a first drum and turned around each o:E bead cores so as to sandwich a stiffener above the bead core between the ply and the turnup portion thereof and then a sidewall rubber layer is applied thereto;
forming a second green case in which one or plural non-expansible or hardly e~pansible cords are spirally wound on a second drum with an outer profile substan-tially corresponding to the carcass form when the tireto be manufactured is mounted on a rim and inflated at a given internal pressure and being capable of contract-ing the above profile to form a second belt layer for belt and then a first belt layer for belt and a tread rubber layer are successively piled thereon;
forming a green ti.re casing in which the first green case taken out :Erom the .f-i.rst dru~ is inserted into the :i.nsi.de of the second green case taken out :Erom the second drum in alignment with each other and then the resulting assembly is brought to a toroidal shape;
and placi.ng the green tire casing in a vulcanizer to conduct the curing thereof. In this case, it is particularly convenient to combinationally e~trude each ,Z~?J
of the sidewa1.1. rubber layer together with a cushion rwbber to be located at its one end.
In the conventional heavy duty low-section pneumatic radial tires, the aforementioned first belt 05 layer or at least two cord plies each containing steel cords, in many cases, incl.ined at a relatively small angl.e of lO~-40 with respect to the equatorial plane of the tire, the cords of which being crossed with each other, are used as a main reinforcement of the belt, so that the rigidity of the belt becomes considerably insufficient in its both side portions as compared with the central portion in case of a lower aspect ratio, and consequently the tread is brought to a concave shape. For this reason, there have been proposed the improvements of the reinforcement characteristics sati.sfying the requirements for the hoop effect of the belt and the rigidity of the tread, for instance, the adjustments of the cord angle, the ply number and the like, bu-t they cannot yet solve the above problems.
~o ~ith the foregoing in mind, the inventors have made a drastic change of the underlying idea, and particularly examined whether or not it is proper to design the first belt layer as the main rei.~forcemeni laye-r :for the belt. As a result, the inven~:ols have founcl that the rigidity of the tread can advanLageously be assured by the second belt layer having the structure as defined above while the first belt layer is rather employed as an au~iliary layer for the belt, whereby a desirable ~ 2;~
distribution of the ground contact pressure is uniformly produced at the ground contact area in the width direction thereof, and the wet skid resistance can be greatly improved without causing uneven wear even when 05 the aspect ratio is as small as 0.4.
The invention will now be described with reference to the accompanying drawings, wherein:
Fig. 1 is a sectional view of an embodiment of the tire according to the invention;
oFigs. 2 and 3 are partially sectional views of the other embodiments of the tire according to the invention, respectively; and Figs. 4 and 5 are schematic views illustrating the main stages in the manufacture of the tire according to the invention, respectively.
In Fig. 1 is shown an embodiment of the heavy duty low-section pneumatic radial tire according to the invention having a tire size of 380/50 R 17.5 14P at such a state that the tire T is mounted onto a rim R of 12.25x17.5 and inflated under an internal pressure of 8.5 kg/cm2.
A reference numeral 1 is a second belt layer for a belt B. In the illustrated embodiment, the second belt layer 1 is a cord ply containing steel cords la (strand construction: lx3+9+15x0.25+1) arranged at an end count of 6 cords/cm over a width wl SUD-stantially equal to a tread width wO and in substantially parallel to the equatorial plane of the tire. A reference numer~l 2 is a first belt layer, which is composed of two cord plies containing steel cords 2a and 2b (strand construction: lx3+6xo~38 mm) arranged at an inclination angle of 20 with respect to the equatorial plane of o~ the tire and extending at an end count of 5.5 cords/cm over widths w2 and w2' slightly narrower than that of the second layerg the cords of which plies being crossed with each other.
A reference numeral 3 is a radial carcass lG composed of a cord ply containing steel cords (strand construction: 1x3+9xo.25+l~ and end count: 6 cords/cm), which extends between a pair of annular bead portions, and is turned up around a bead core 4 embedded in the bead portion so as to sandwich a stiffener 5 (composed of two hard and soft rubber stocks in the illustrated embodiment) between the carcass and the turnup portion thereof, and is reinforced at the outside of the turnup portion with a chafer 6 of steel cords (strand construc-tion: lx3+9+15x0.15~1, and end count: 26 cords/25.4 mm) inclined at an angle of 60~ with respect to the radial line of the tire.
A tread rubber t is piled onto -the belt B
consisti.ng of the :Eirst bel.t 1.aye~ 2 and the second belt layer 1., and unitecl aL both side re~ions of the 2s second belt layer 1 with a cushion rubber C interposed between the second belt layer 1 and the radial carcass
It is, therefore, an object of the invention to effectively solve the problems inherent to the conventional heavy duty low-section pneumatic radial tire and to provide an advantageous process for manufacturing a heavy duty low-section pneumatic radial tire of this type without suffering the disadvantages ..;.
~Z~a. ~Z ~7 inherent to the conventional tire as clescribed above.
According to the invention, there is the provision of a heavy duty low-section pneumatic radial tire comprising a radia]. carcass toroidally extending 05 be-tween a pair of annular bead portions, a belt composed of plura] ply layers successively superimposed one upon the other around a crown portion of the carcass, and a tread rubber having substantially the same width as the maximum width of the belt; said belt being a combina-1o tion of a first belt layer with a second belt layer, said first belt layer being composed of at least two cord plies each containing cords inclined at a small angle with respect to the equatorial plane of the tire, the cords of which plies being crossed with each other with respect to the equatorial plane, said second beltlayer being composed of at leas-t one cord ply containing non-expansible or hardly expansible cords arranged in substantially parallel to the equatorial plane and extending over both sides of the first belt layer between the carcass and the first belt layer.
In the preferred embodiments of the invention, the radial carcass is composed of a si.ngle to several plies of the fiber cords each macle of nylon E:iber, polyester fiber o:r preferably Kevlar .tiber, or of a single or two plies at the most of the steel cords.
Further, the first belt layer uses the above fiber cords or steel cords arranged at an inclination angle of lO-~0 with respect to the equatorial plane of the l~z~
tire, while the second belt layer uses cords having a modulus of elast:icity of not less than 30X104 kg/cm2 and extends over a width wider -than that of the first belt layer and at substantially the same width as that 05 of the tread rubber. ~nd also, the second belt layer is arranged on the carcass such that at least 50%, preferably 60-80% of the second belt layer at its central portion is located along the cord pass line at the crown portion of the carcass, while the remaining o both side portions of the second belt layer are disposed on cushion rubbers each located at the shoulder portion of the carcass. Moreover, the second belt layer has a bearing ratio on resistance to tensile load of 60-90%
of the sum of the resistances to tensile load of the first and second belt layers per unit width calculated by the following formula:
T Ncos~2/Rm P
, wherein T is a tenacity of a cord, N is an end count of cords per unit width as measured at right angle to the cord, ~ is an inclination angle of the cord with respect to the equator:i.al plane of the tire, ~m is a radi~ls of each cord ply being a d:istance between the cord center and the tire center and P is a normal i.nternal pressure of the tire. ~n the tire according to the invention, it is preferable that the aspect ratio H/W is within a range of 0.9 o.i~, preferably ~ 2~ 2 ~
0.7-0.~ and the carcass flatness Rl/W' is within a range o:E 3-10, preferably 5-lO.
The heavy duLy low-section pneuma-tic radial tire according to the invention may advantageowsly be 05 manufactured by a process comprising the steps of:
forming a first green case in which a ply(s) for carcass is placed on an outer circumference of a first drum and turned around each o:E bead cores so as to sandwich a stiffener above the bead core between the ply and the turnup portion thereof and then a sidewall rubber layer is applied thereto;
forming a second green case in which one or plural non-expansible or hardly e~pansible cords are spirally wound on a second drum with an outer profile substan-tially corresponding to the carcass form when the tireto be manufactured is mounted on a rim and inflated at a given internal pressure and being capable of contract-ing the above profile to form a second belt layer for belt and then a first belt layer for belt and a tread rubber layer are successively piled thereon;
forming a green ti.re casing in which the first green case taken out :Erom the .f-i.rst dru~ is inserted into the :i.nsi.de of the second green case taken out :Erom the second drum in alignment with each other and then the resulting assembly is brought to a toroidal shape;
and placi.ng the green tire casing in a vulcanizer to conduct the curing thereof. In this case, it is particularly convenient to combinationally e~trude each ,Z~?J
of the sidewa1.1. rubber layer together with a cushion rwbber to be located at its one end.
In the conventional heavy duty low-section pneumatic radial tires, the aforementioned first belt 05 layer or at least two cord plies each containing steel cords, in many cases, incl.ined at a relatively small angl.e of lO~-40 with respect to the equatorial plane of the tire, the cords of which being crossed with each other, are used as a main reinforcement of the belt, so that the rigidity of the belt becomes considerably insufficient in its both side portions as compared with the central portion in case of a lower aspect ratio, and consequently the tread is brought to a concave shape. For this reason, there have been proposed the improvements of the reinforcement characteristics sati.sfying the requirements for the hoop effect of the belt and the rigidity of the tread, for instance, the adjustments of the cord angle, the ply number and the like, bu-t they cannot yet solve the above problems.
~o ~ith the foregoing in mind, the inventors have made a drastic change of the underlying idea, and particularly examined whether or not it is proper to design the first belt layer as the main rei.~forcemeni laye-r :for the belt. As a result, the inven~:ols have founcl that the rigidity of the tread can advanLageously be assured by the second belt layer having the structure as defined above while the first belt layer is rather employed as an au~iliary layer for the belt, whereby a desirable ~ 2;~
distribution of the ground contact pressure is uniformly produced at the ground contact area in the width direction thereof, and the wet skid resistance can be greatly improved without causing uneven wear even when 05 the aspect ratio is as small as 0.4.
The invention will now be described with reference to the accompanying drawings, wherein:
Fig. 1 is a sectional view of an embodiment of the tire according to the invention;
oFigs. 2 and 3 are partially sectional views of the other embodiments of the tire according to the invention, respectively; and Figs. 4 and 5 are schematic views illustrating the main stages in the manufacture of the tire according to the invention, respectively.
In Fig. 1 is shown an embodiment of the heavy duty low-section pneumatic radial tire according to the invention having a tire size of 380/50 R 17.5 14P at such a state that the tire T is mounted onto a rim R of 12.25x17.5 and inflated under an internal pressure of 8.5 kg/cm2.
A reference numeral 1 is a second belt layer for a belt B. In the illustrated embodiment, the second belt layer 1 is a cord ply containing steel cords la (strand construction: lx3+9+15x0.25+1) arranged at an end count of 6 cords/cm over a width wl SUD-stantially equal to a tread width wO and in substantially parallel to the equatorial plane of the tire. A reference numer~l 2 is a first belt layer, which is composed of two cord plies containing steel cords 2a and 2b (strand construction: lx3+6xo~38 mm) arranged at an inclination angle of 20 with respect to the equatorial plane of o~ the tire and extending at an end count of 5.5 cords/cm over widths w2 and w2' slightly narrower than that of the second layerg the cords of which plies being crossed with each other.
A reference numeral 3 is a radial carcass lG composed of a cord ply containing steel cords (strand construction: 1x3+9xo.25+l~ and end count: 6 cords/cm), which extends between a pair of annular bead portions, and is turned up around a bead core 4 embedded in the bead portion so as to sandwich a stiffener 5 (composed of two hard and soft rubber stocks in the illustrated embodiment) between the carcass and the turnup portion thereof, and is reinforced at the outside of the turnup portion with a chafer 6 of steel cords (strand construc-tion: lx3+9+15x0.15~1, and end count: 26 cords/25.4 mm) inclined at an angle of 60~ with respect to the radial line of the tire.
A tread rubber t is piled onto -the belt B
consisti.ng of the :Eirst bel.t 1.aye~ 2 and the second belt layer 1., and unitecl aL both side re~ions of the 2s second belt layer 1 with a cushion rubber C interposed between the second belt layer 1 and the radial carcass
3 and a side rubber S.
In the illustrated embodiment, the tire T has ~z~
Lhe following climensions oE W-380 mm, wo=285 mrn, w1=2~0 mm, w2=210 mm, w2l=140 mm and w3=195 mm corre-sponding to a distance between the opposed ends of the cushion rub`bers C, in which the second belt layer 1 05 extends at its central portion over the distance W3 along the cord pass line of the radial carcass 3 in direct contact therewith and each of the remaining side portions is located onto the cushion rubber C.
The height H of the tire as measured from the bead base of the bead portion is 18S mm, thus the aspect ratio expressed by H/W being about 50%. On the other hand, as the radiws Ro of the tread crown is 2,500 mm and the radius ~l of the crown portion of the carcass 3 contacting wit~ the second belt layer l is 2,465 mm, the carcass flatness expressed by the ratio of the radius of the crown portion of the carcass to the maximum carcass width ~W'=W-2g) (g is a thickness of the sidewall rubber at the position of the maximum width. In the illustrated embodiment, g is 4 mm.) is 6.6.
When the tenacity T per one cord of the second belt layer 1 in the vicinity of the equatorial plane of the tire -ls 320 kg and the raclius Rm of the cord ply of the belt is 38 cm and the internal presswre P is 8.5 kg/cm~, the resistance to tensile load per unit width gives 5.9 as calculated from the afore-mentioned e~uation, while the tenacity T of the first belt :Layer 2 is 185 kg and hence the resistance to ~ 2~
tensile loacl thereof is 2.~,. Accordingly, the bearing ratio of the second belt layer 1 in the sum of these resistances to tensile load is 5 9~2 gxloo~68%.
In order to obtain a more uniform ground 05 contact pressure, it is desirable that the resistance to tensile load of the second belt layer 1 is larger at both side edge portions than at the central portion corresponding to the crown portion o the carcass 3 as -the aspect ratio becomes particularly smaller. Accord-ingly, in order to further enhance the durability, although such an application is disadvantageous in view of the tire manufacture as mentioned later, an auxiliary layer 11 of cords arranged at an inclination angle of not less than 40, preferably not less than 60 with respect to the equatorial plane of the tire may be arranged inside or outside the second belt layer 1, preferably adjacent thereto in the radial direction at a width substantially equal to that of the layer 1.
In the belt B, the width wl of the second belt layer 1 is desirable to be 90-110%, preferably 95-105% with respect to the width wO of -the tread from the standpoint of the belt durabi.lity. The width W3 of the second belt layer Iying alc)ng the corcl pass l-ine in the crown portion of the carcass 3 is desirable to be within a range of 50-90%, preferably 60-~0% with respect to the above width wl rom the standpoint of uniformity of the ground contact pressure at the rotation of the tire under a load as well as the belt durability.
~ZS~
In order to prevent possible end separation at the side edge portions of the flrst belt layer 2, the width w2 of the first belt layer 2 in the belt B is in a range of 60-80%, preferably 70-80% with respect to 05 the above width w1.
As previously mentioned, the first and second belt 1ayers of the belt B may optionally take a proper combination of various cord materials, b-ut in the heavy duty low-section pneumatic radial tires of this type, 0 the belt layers including the carcass ply are preferable to be composed of steel cords as in the illwstrated embodiment.
Moreover, the second belt layer 1 of the be]t B may be the single ply as in the illustrated embodiment or may be composed of plural plies. In the latter case, at least one cord ply is continuous in the width direction, while the remaining ply or plies may be properly divided in the width direction into plural bands.
Preferably, the radius Ro of curvature of the tread t is made substantially equal to that R1 of the crown portion of the carcass 3.
Thus, the inven~ion is app:l:icabLe to tires wherein the aspect ratio ~I/W is in a ran~e of 0.4-0.9, particularly 0.~l-0.65 and the :internal pressure is within a ran~e of not more than l.4 times, preferably not more than l.25 times the normal :internal pressure.
The performances of the tire A of the invention ,~
~2~
illustraLed in Fig. I and eA~plained above were compared with those of the conventional. tires having the following belt reinforcement.
Conven-tional ti.re B:
os This tire had the conventional belt structure that onto the crown portion of the carcass 3 as shown in Fig. 1 were s-uccessively superimposed a first layer of steel cords arranged inclined at 65 wi-th respect to the equatorial plane of the tire, a second layer of steel cords inclined at 15 in the same direction as that of the first layer and having a width wider than in that of the first layer, and a third layer of steel cords inclined at 15 in the direction opposite to that of the first layer and having a width relatively narrower than that of the second layer, all of these steel cords having the strand construction of lx3~9~l5xo.~5+
Conventional tire C:
This tire has the conventiona] belt structure that two layers of steel cords each having the strand construction of lx3+6x0.38 were arranged on the crown portion at t:he same cord angles as those of the second and third layers of the tire B ancl a steel corcl of lx3+9+15x0.25+1. was sp-lral:l.y wouncl the:rea-round :in paral.lel to the equatoricl:L pl.ane o:l~ the t.:i:re.
The items, conclitions and results o:E the comparison test are shown in the :Eollowing Table.
~2~C.?l:?Z~
~ ~ ~ ---~
~ t _ ~ _ e ~ ~
~o o o. ~o ~ . , . . ~
~ O ~D ~0 _ .. __~ __ _ a~ o s., .
~ ~
e ~ 3 ~ ~ ~ a o ~ ~ ~ O
o ~ 3 C ~ ~ ~ o o ~ ~ a) ~:: O O U d o~
o a~ ~ 3 ,~ o ~ ~ o ~" ~ o ,S~ ,d ,5 ~ 00 ~ ~ ~ . d ~ ~ o ~ o ~ c~ aJ aJ o J-- aJ ~ ~ O ~ ~ ~ 00 3 c~ ~ o ~ p~
2 ~ ~ 4_j h ~,1 ~ r~ ~ ~ ~1 o ~ 4~ ~~ ~ d ~ ~ 00 ~1 O i~ o ~ ~ o .~ ~
V ~ ~ ~ ~ ~ ~
~; 3 o u~o - a~ 3 33 ~,~ c~ o t~ ~i 3 U 'i 0~ ^,~ 4 ~ q ~ 4~ ~
U 4i In 4i ~d~ 4i ' I O O ~~ 4i ,I D ~ O
4i ) SiU lq 4i ^ U 00 O .Y O S-i O
q ~ O O O~ ~ O O C~l S~ O OC D 3 d OC ~ ~, rO~ ~j O ~ O ~j ~q ~ o~ a~ ~ ~ ~i o q ~ S i ~ ~o ~ ri C.l 4~ ,Y 3 a~ d ooo o u ~ ~ ~ E ~ o ,-i d ~ ~ ~l d ~S --~ r--i O ~ U ~ n ~ ri o _E~ 3 ):4 ~ o ,i ~ o rq i ~j ^ E~
-- d ~ u .
'~ 4~ U
E 4 o ::~ QJ s i o ~11 U ~ri Li 1;) ~ ~1 C~
~i d D ~ ~,i 3 0 ~, E
,~ ~ ~1 U 3 ~ _~ 3 rC1 i ,qu3_ 3 ~ ~
~., ?A,',;~
~ s seen from the above results, in the tire according to the invention, the uneven wear is con-siderably reduced by improving the belt reinforcing structure as mentioned above to make the distribution 05 of ground contact pressure in the widthwise direction appropriate, and also the reduction of belt weight and the improving effect for preventing the belt separation and cord b-reaking are conspicuous.
Figs. 4 and 5 schematically illustrate an advantageous process for manufacturing the tire according to the invention referring to the stages for the formation of a first green case 7 and a second green case 8.
In the manufacture of the first green case 7 with reference to Fig. 4, a ply material(s) 3' for the carcass 3 is first wound around an outer circumference of a first drum 9 with a col.lapsible cylindrical shape according to the conventional manner, and thereafter both surplus portions 3" of the ply material 3' are turned around bead cores 4 located at both sides of the drum so as to sandwich two soft and hard rubber stocks 5' constituting the stiffener rubber 5, and then a pai.r of rubber materi.als S' each consl:it~lt~ g the si.dewaLl.
rubber layer S are lami.nated to a part of the ply material 3' and its both turnup porti.on through necessary wire chafer materials 6' ancl rubber chafer materials 6".
Next, the outer diameter of the first drum 9 is reduced to take out the first green case 7 from the drum.
In this case, it is desirable that the rubber material S' is simultaneously extruded as a composite material together with a rubber stock C' corresponding to the cushion rubber C to be located inward thereof.
05 The rubber stock C' has preferably the rubber proper-ties similar to those of a coating rubber for the carcass 3 and belt as mentioned later.
In the manufacture of the second green case 8 as shown in Fig. 5, single steel cord la or a bundle of 0 two or at most three steel cords la constituting the second belt layer l is first wound on an outer circumference of a second drum lO with a collapsible cylindrical shape in a spiral profile aligned with the cord pass line in the crown portion of the carcass 3 of the tire to be manufactured under a predetermined internal pressure. Although not shown, this winding may be performed in two or more layers if necessary.
Alternative]y, a bias cord fabric composed of these cords may be turned around the drum with its ends overlapped with each other in the orientation direction of the cords.
With respect to the first belt Iclyer 2, ~he cords 2a and 2b are crossecl with each other in the same cord arrangement as that of the convent:ional main belt reinforcement and piled in two piles as shown in Fig. 5 or in a number of piles near two. Therefore, a tread rubber t is piled on the first belt layer 2.
Then, the thus formed second green case 8 is ~ ~3~
taken out by reducing the outer diameter of the second drum 10 3 into the inside of which is inserted the first green case 7 in alignment with each other. The resulting assembly is toroidally transformed to form a green tire 05 casing, which is cured in a vlllcanizer in the conven-tional manner~ whereby the radial tire as shown in Fig. 1 can easily be obtained.
According to the invention, not only the uniform distribution of the ground contact pressure in 0 heavy duty low-section pneumatic radial tires havin an aspect ratio of up to 0.~ can be advantageously realized by improving the belt reinforcement structure, but also the weight-saving of the tire together with the prevention of uneven wear of the tread can be obtained by reducing the belt weight without producing the belt end separation and cord breaking. Further, the invention particularly facilitates the manufacture of such heavy duty low~section pneumatic radial tires.
In the illustrated embodiment, the tire T has ~z~
Lhe following climensions oE W-380 mm, wo=285 mrn, w1=2~0 mm, w2=210 mm, w2l=140 mm and w3=195 mm corre-sponding to a distance between the opposed ends of the cushion rub`bers C, in which the second belt layer 1 05 extends at its central portion over the distance W3 along the cord pass line of the radial carcass 3 in direct contact therewith and each of the remaining side portions is located onto the cushion rubber C.
The height H of the tire as measured from the bead base of the bead portion is 18S mm, thus the aspect ratio expressed by H/W being about 50%. On the other hand, as the radiws Ro of the tread crown is 2,500 mm and the radius ~l of the crown portion of the carcass 3 contacting wit~ the second belt layer l is 2,465 mm, the carcass flatness expressed by the ratio of the radius of the crown portion of the carcass to the maximum carcass width ~W'=W-2g) (g is a thickness of the sidewall rubber at the position of the maximum width. In the illustrated embodiment, g is 4 mm.) is 6.6.
When the tenacity T per one cord of the second belt layer 1 in the vicinity of the equatorial plane of the tire -ls 320 kg and the raclius Rm of the cord ply of the belt is 38 cm and the internal presswre P is 8.5 kg/cm~, the resistance to tensile load per unit width gives 5.9 as calculated from the afore-mentioned e~uation, while the tenacity T of the first belt :Layer 2 is 185 kg and hence the resistance to ~ 2~
tensile loacl thereof is 2.~,. Accordingly, the bearing ratio of the second belt layer 1 in the sum of these resistances to tensile load is 5 9~2 gxloo~68%.
In order to obtain a more uniform ground 05 contact pressure, it is desirable that the resistance to tensile load of the second belt layer 1 is larger at both side edge portions than at the central portion corresponding to the crown portion o the carcass 3 as -the aspect ratio becomes particularly smaller. Accord-ingly, in order to further enhance the durability, although such an application is disadvantageous in view of the tire manufacture as mentioned later, an auxiliary layer 11 of cords arranged at an inclination angle of not less than 40, preferably not less than 60 with respect to the equatorial plane of the tire may be arranged inside or outside the second belt layer 1, preferably adjacent thereto in the radial direction at a width substantially equal to that of the layer 1.
In the belt B, the width wl of the second belt layer 1 is desirable to be 90-110%, preferably 95-105% with respect to the width wO of -the tread from the standpoint of the belt durabi.lity. The width W3 of the second belt layer Iying alc)ng the corcl pass l-ine in the crown portion of the carcass 3 is desirable to be within a range of 50-90%, preferably 60-~0% with respect to the above width wl rom the standpoint of uniformity of the ground contact pressure at the rotation of the tire under a load as well as the belt durability.
~ZS~
In order to prevent possible end separation at the side edge portions of the flrst belt layer 2, the width w2 of the first belt layer 2 in the belt B is in a range of 60-80%, preferably 70-80% with respect to 05 the above width w1.
As previously mentioned, the first and second belt 1ayers of the belt B may optionally take a proper combination of various cord materials, b-ut in the heavy duty low-section pneumatic radial tires of this type, 0 the belt layers including the carcass ply are preferable to be composed of steel cords as in the illwstrated embodiment.
Moreover, the second belt layer 1 of the be]t B may be the single ply as in the illustrated embodiment or may be composed of plural plies. In the latter case, at least one cord ply is continuous in the width direction, while the remaining ply or plies may be properly divided in the width direction into plural bands.
Preferably, the radius Ro of curvature of the tread t is made substantially equal to that R1 of the crown portion of the carcass 3.
Thus, the inven~ion is app:l:icabLe to tires wherein the aspect ratio ~I/W is in a ran~e of 0.4-0.9, particularly 0.~l-0.65 and the :internal pressure is within a ran~e of not more than l.4 times, preferably not more than l.25 times the normal :internal pressure.
The performances of the tire A of the invention ,~
~2~
illustraLed in Fig. I and eA~plained above were compared with those of the conventional. tires having the following belt reinforcement.
Conven-tional ti.re B:
os This tire had the conventional belt structure that onto the crown portion of the carcass 3 as shown in Fig. 1 were s-uccessively superimposed a first layer of steel cords arranged inclined at 65 wi-th respect to the equatorial plane of the tire, a second layer of steel cords inclined at 15 in the same direction as that of the first layer and having a width wider than in that of the first layer, and a third layer of steel cords inclined at 15 in the direction opposite to that of the first layer and having a width relatively narrower than that of the second layer, all of these steel cords having the strand construction of lx3~9~l5xo.~5+
Conventional tire C:
This tire has the conventiona] belt structure that two layers of steel cords each having the strand construction of lx3+6x0.38 were arranged on the crown portion at t:he same cord angles as those of the second and third layers of the tire B ancl a steel corcl of lx3+9+15x0.25+1. was sp-lral:l.y wouncl the:rea-round :in paral.lel to the equatoricl:L pl.ane o:l~ the t.:i:re.
The items, conclitions and results o:E the comparison test are shown in the :Eollowing Table.
~2~C.?l:?Z~
~ ~ ~ ---~
~ t _ ~ _ e ~ ~
~o o o. ~o ~ . , . . ~
~ O ~D ~0 _ .. __~ __ _ a~ o s., .
~ ~
e ~ 3 ~ ~ ~ a o ~ ~ ~ O
o ~ 3 C ~ ~ ~ o o ~ ~ a) ~:: O O U d o~
o a~ ~ 3 ,~ o ~ ~ o ~" ~ o ,S~ ,d ,5 ~ 00 ~ ~ ~ . d ~ ~ o ~ o ~ c~ aJ aJ o J-- aJ ~ ~ O ~ ~ ~ 00 3 c~ ~ o ~ p~
2 ~ ~ 4_j h ~,1 ~ r~ ~ ~ ~1 o ~ 4~ ~~ ~ d ~ ~ 00 ~1 O i~ o ~ ~ o .~ ~
V ~ ~ ~ ~ ~ ~
~; 3 o u~o - a~ 3 33 ~,~ c~ o t~ ~i 3 U 'i 0~ ^,~ 4 ~ q ~ 4~ ~
U 4i In 4i ~d~ 4i ' I O O ~~ 4i ,I D ~ O
4i ) SiU lq 4i ^ U 00 O .Y O S-i O
q ~ O O O~ ~ O O C~l S~ O OC D 3 d OC ~ ~, rO~ ~j O ~ O ~j ~q ~ o~ a~ ~ ~ ~i o q ~ S i ~ ~o ~ ri C.l 4~ ,Y 3 a~ d ooo o u ~ ~ ~ E ~ o ,-i d ~ ~ ~l d ~S --~ r--i O ~ U ~ n ~ ri o _E~ 3 ):4 ~ o ,i ~ o rq i ~j ^ E~
-- d ~ u .
'~ 4~ U
E 4 o ::~ QJ s i o ~11 U ~ri Li 1;) ~ ~1 C~
~i d D ~ ~,i 3 0 ~, E
,~ ~ ~1 U 3 ~ _~ 3 rC1 i ,qu3_ 3 ~ ~
~., ?A,',;~
~ s seen from the above results, in the tire according to the invention, the uneven wear is con-siderably reduced by improving the belt reinforcing structure as mentioned above to make the distribution 05 of ground contact pressure in the widthwise direction appropriate, and also the reduction of belt weight and the improving effect for preventing the belt separation and cord b-reaking are conspicuous.
Figs. 4 and 5 schematically illustrate an advantageous process for manufacturing the tire according to the invention referring to the stages for the formation of a first green case 7 and a second green case 8.
In the manufacture of the first green case 7 with reference to Fig. 4, a ply material(s) 3' for the carcass 3 is first wound around an outer circumference of a first drum 9 with a col.lapsible cylindrical shape according to the conventional manner, and thereafter both surplus portions 3" of the ply material 3' are turned around bead cores 4 located at both sides of the drum so as to sandwich two soft and hard rubber stocks 5' constituting the stiffener rubber 5, and then a pai.r of rubber materi.als S' each consl:it~lt~ g the si.dewaLl.
rubber layer S are lami.nated to a part of the ply material 3' and its both turnup porti.on through necessary wire chafer materials 6' ancl rubber chafer materials 6".
Next, the outer diameter of the first drum 9 is reduced to take out the first green case 7 from the drum.
In this case, it is desirable that the rubber material S' is simultaneously extruded as a composite material together with a rubber stock C' corresponding to the cushion rubber C to be located inward thereof.
05 The rubber stock C' has preferably the rubber proper-ties similar to those of a coating rubber for the carcass 3 and belt as mentioned later.
In the manufacture of the second green case 8 as shown in Fig. 5, single steel cord la or a bundle of 0 two or at most three steel cords la constituting the second belt layer l is first wound on an outer circumference of a second drum lO with a collapsible cylindrical shape in a spiral profile aligned with the cord pass line in the crown portion of the carcass 3 of the tire to be manufactured under a predetermined internal pressure. Although not shown, this winding may be performed in two or more layers if necessary.
Alternative]y, a bias cord fabric composed of these cords may be turned around the drum with its ends overlapped with each other in the orientation direction of the cords.
With respect to the first belt Iclyer 2, ~he cords 2a and 2b are crossecl with each other in the same cord arrangement as that of the convent:ional main belt reinforcement and piled in two piles as shown in Fig. 5 or in a number of piles near two. Therefore, a tread rubber t is piled on the first belt layer 2.
Then, the thus formed second green case 8 is ~ ~3~
taken out by reducing the outer diameter of the second drum 10 3 into the inside of which is inserted the first green case 7 in alignment with each other. The resulting assembly is toroidally transformed to form a green tire 05 casing, which is cured in a vlllcanizer in the conven-tional manner~ whereby the radial tire as shown in Fig. 1 can easily be obtained.
According to the invention, not only the uniform distribution of the ground contact pressure in 0 heavy duty low-section pneumatic radial tires havin an aspect ratio of up to 0.~ can be advantageously realized by improving the belt reinforcement structure, but also the weight-saving of the tire together with the prevention of uneven wear of the tread can be obtained by reducing the belt weight without producing the belt end separation and cord breaking. Further, the invention particularly facilitates the manufacture of such heavy duty low~section pneumatic radial tires.
Claims (10)
1. A heavy duty low-section pneumatic radial tire comprising a radial carcass toroidally extending between a pair of annular bead portions, a belt composed of plural ply layers successively superimposed one upon the other around a crown portion of the carcass, and a tread rubber having substantially the same width as the maximum width of the belt; said belt being combina-tion of a first belt layer and a second belt layer, said first belt layer being composed of at least two cord plies each containing cords inclined at a small angle with respect to the equatorial plane of the tire, the cords of which plies being crossed with each other with respect to the equatorial plane, said second belt layer being composed of at least one cord ply containing non-expansible or hardly expansible cords arranged in substantially parallel to the equatorial plane and extending over both sides of the first belt layer between the first belt layer and the carcass.
2. The heavy duty low-section pneumatic radial tire according to claim 1, wherein said radial carcass is composed of a single to several plies of cords selected from the group consisting of non-expansible or hardly expansible aromatic polyamide cords and steel cords.
3. The heavy duty low-section pneuatic radial tire according to claim 1, wherein said first belt layer is composed of fiber cords of a material selected from the group consisting of nylon, polyester and aromatic polyamide, said cords being arranged at an inclination angle of 10-40° with respect to the equatorial plane of the tire.
4. The heavy duty low-section pneumatic radial tire according to claim 1, wherein said first belt layer is composed of strand cords of steel wires arranged at an inclination angle of 10-40° with respect to the equatorial plane of the tire.
5. The heavy duty low-section pneumatic radial tire according to claim 1, wherein said second belt layer is composed of cords having a modulus of elasticity of not less than 30X104 kg/cm2 and extends over a width wider than that of the first belt layer and at substan-tially the same width as that of the tread rubber.
6. The heavy duty low-section pneumatic radial tire according to claim 1, wherein said second belt layer is arranged on the carcass such that at least 50%, preferably 60-80% of the second belt layer at its central portion is located along the cord pass line at the crown portion of the carcass in direct contact therewith, while the remaining both side portions are disposed on cushion rubbers each located at the shoulder portions of the carcass.
7. The heavy duty low-section pneumatic radial tire according to claim 1, wherein said second belt layer has a bearing ratio on resistance to tensile load of 60-90% of the sum of the resistances to tensile load of said first and second belt layers per unit width calculated by the equation:
T.Ncos.alpha.2/Rm.P
, wherein T is a tenacity of a cord, N is an end count of cords per unit width as measured at right angle to the cord, .alpha. is an inclination angle of the cord with respect to the equatorial plane of the tire, Rm is a radius of each cord ply being a distance between the cord center and the tire center and P is a normal internal pressure of the tire.
T.Ncos.alpha.2/Rm.P
, wherein T is a tenacity of a cord, N is an end count of cords per unit width as measured at right angle to the cord, .alpha. is an inclination angle of the cord with respect to the equatorial plane of the tire, Rm is a radius of each cord ply being a distance between the cord center and the tire center and P is a normal internal pressure of the tire.
8. The heavy duty low-section pneumatic radial tire according to claim 1, wherein said tire has an aspect ratio H/W of 0.9-0.4, preferably 0.7-0.4 and a carcass flatness R1/W' of 3-10, preferably 5-10.
9. A process for manufacturing a heavy duty low-section pneumatic radial tire, which comprises the steps of.
forming a first green case in which a ply(s) for carcass is placed on an outer circumference o-f a first drum and turned around each of bead cores so as to sandwich a stiffener above the bead core between the ply and the turnup portion thereof and a sidewall rubber layer is applied thereto;
forming a second green case in which one or plural non-expansible or hardly expansible cords are spirally wound on a second drum with an outer profile substan-tially corresponding to the carcass form when the tire to be manufactured is mounted on a rim and inflated at a given internal pressure and being capable of contract-ing the above profile to form a second belt layer for belt and a first belt layer for belt and a tread rubber layer are successively piled thereon;
forming a green tire casing in which the first green case taken out from the first drum is inserted into the inside of the second green case taken out from the second drum in alignment with each other and then the resulting assembly is brought to a toroidal form;
and placing the green tire casing in a vulcanizer to conduct the curing thereof.
forming a first green case in which a ply(s) for carcass is placed on an outer circumference o-f a first drum and turned around each of bead cores so as to sandwich a stiffener above the bead core between the ply and the turnup portion thereof and a sidewall rubber layer is applied thereto;
forming a second green case in which one or plural non-expansible or hardly expansible cords are spirally wound on a second drum with an outer profile substan-tially corresponding to the carcass form when the tire to be manufactured is mounted on a rim and inflated at a given internal pressure and being capable of contract-ing the above profile to form a second belt layer for belt and a first belt layer for belt and a tread rubber layer are successively piled thereon;
forming a green tire casing in which the first green case taken out from the first drum is inserted into the inside of the second green case taken out from the second drum in alignment with each other and then the resulting assembly is brought to a toroidal form;
and placing the green tire casing in a vulcanizer to conduct the curing thereof.
10. The process according to claim 9, wherein said sidewall rubber layer is combinationally extruded together with a cushion rubber to be located at its one end.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000457082A CA1209022A (en) | 1984-06-21 | 1984-06-21 | Heavy duty low-section pneumatic radial tire and a process for manufacturing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000457082A CA1209022A (en) | 1984-06-21 | 1984-06-21 | Heavy duty low-section pneumatic radial tire and a process for manufacturing the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1209022A true CA1209022A (en) | 1986-08-05 |
Family
ID=4128140
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000457082A Expired CA1209022A (en) | 1984-06-21 | 1984-06-21 | Heavy duty low-section pneumatic radial tire and a process for manufacturing the same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1209022A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102762389A (en) * | 2010-02-19 | 2012-10-31 | 大陆轮胎德国有限公司 | Pneumatic vehicle tire |
| CN104870214A (en) * | 2012-12-20 | 2015-08-26 | 米其林集团总公司 | Tire crown for heavy civil engineering vehicle |
| CN104870213B (en) * | 2012-12-20 | 2017-03-22 | 米其林集团总公司 | Tire crown for heavy civil engineering vehicle |
| CN112976944A (en) * | 2019-12-18 | 2021-06-18 | 住友橡胶工业株式会社 | Heavy-duty tubeless tire and manufacturing method thereof |
-
1984
- 1984-06-21 CA CA000457082A patent/CA1209022A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102762389A (en) * | 2010-02-19 | 2012-10-31 | 大陆轮胎德国有限公司 | Pneumatic vehicle tire |
| US10696098B2 (en) | 2010-02-19 | 2020-06-30 | Continental Reifen Deutschland Gmbh | Pneumatic vehicle tire |
| CN104870214A (en) * | 2012-12-20 | 2015-08-26 | 米其林集团总公司 | Tire crown for heavy civil engineering vehicle |
| CN104870213B (en) * | 2012-12-20 | 2017-03-22 | 米其林集团总公司 | Tire crown for heavy civil engineering vehicle |
| CN104870214B (en) * | 2012-12-20 | 2017-03-22 | 米其林集团总公司 | Tire crown for heavy civil engineering vehicle |
| US10046604B2 (en) | 2012-12-20 | 2018-08-14 | Compagnie Generale Des Etablissements Michelin | Tire crown for heavy civil engineering vehicle |
| CN112976944A (en) * | 2019-12-18 | 2021-06-18 | 住友橡胶工业株式会社 | Heavy-duty tubeless tire and manufacturing method thereof |
| CN112976944B (en) * | 2019-12-18 | 2024-02-13 | 住友橡胶工业株式会社 | Tubeless tire for heavy load and method of manufacturing the same |
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