CA1169343A - Pneumatic radial tires - Google Patents
Pneumatic radial tiresInfo
- Publication number
- CA1169343A CA1169343A CA000407838A CA407838A CA1169343A CA 1169343 A CA1169343 A CA 1169343A CA 000407838 A CA000407838 A CA 000407838A CA 407838 A CA407838 A CA 407838A CA 1169343 A CA1169343 A CA 1169343A
- Authority
- CA
- Canada
- Prior art keywords
- belt
- tire
- carcass
- modulus
- rubber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
- B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Tires In General (AREA)
Abstract
Abstract of the Disclosure A pneumatic radial tire is disclosed, which comprises a body reinforcement including in combination of a carcass composed of at least one rubberized ply contain-ing organic fiber cords arranged in a substantially radial plane of the tire and wound around a bead core from the inside toward the outside thereof and a belt composed of at least two rubberized layers superimposed about a crown portion of the carcass, each of which containing high elasticity cords inclined at a relatively small angle with respect to the circumferential direction of the tire center and the cords of these layers being crossed with each other, and further comprising sidewall rubbers disposed at both sides of the carcass and a tread rubber disposed on the outer surface of the belt. In this tire, at least one rubberized layer constituting the belt comprises a coating rubber having a modulus at 25% elongation of 4-10 kg/cm2 and a dynamic modulus of 16.2-40.5 kg/cm2.
Description
6~3~3 This invention relates to pneumatic radial tires, and more particularly to pneumatic radial tires which can advantageously realize the improvement of rolling resistance without actually causing deterioration of other tire performances.
In general, conventional tires with a so-called radial structure are recognized to be practical under usual use conditions, particularly under an internal pressure of
In general, conventional tires with a so-called radial structure are recognized to be practical under usual use conditions, particularly under an internal pressure of
2.0 kg/cm at most~ Now, the contribution ratio of each portion constituting the tire to the rolling resistance was analyzed under the usual use condition and as a result, it ; has been confirmed that the contribution ratio is distri-buted into 34% in tread portion, 27% in buttress portion, 25% in sidewall portion and about 14% in bead portion.
From the above, it is apparent that the tread rubber has a largest contribution ratio to rolling resistance.
Thexefore, in order to reduce the rolling resistance by decreasing the internal friction loss of tread rubber, it is usually performed to decrea,se loss tangent (tan ~) and ~-20 loss modulus (G") and raise rebound resilience in the rubber composition for the tread.
In this case, however, the wet performance being an important property in this type of the tire is undesirably deteriorated in accordance with the degree of improving the .:
rolling resistance. This contrary relationship is a function of rebound resilience of the tread rubber. Therefore, this .
countermeasure cannot expect the remarkable improvement of the rolling resistance unless there is taken another means for preventing the ~ .
~ ~ 2- ~
. . ,, . _, ~ ~ 6~3~3 deterioration of the wet performance. Particularly, there is found no effective means for holding the wet performance, so that the above countermeasure is not too ef~ective in - practice.
As the second countermeasure, it is attempted to apply rubber having substantially the same composition as used in the tread rubber -to sidewalls o~ the tire. In this attempt, however, the rolling resistance is practically improved only by about 3% or less, while -the damping characteristic against vibration produced in the tire is deteriorated to adversely affect the signi~icant ride feeling of the tire.
Besides, there are adopted various means for reducing the rolling resistance by weight-saving of tire, for example, by changing the carcass from two ply structure to single ply structure or by making the width of the belt narrow, but these means cause the de-teriora-tion of the cornering stability due to the reduction o~ rigidity in main reinforced portions of the tire. As a resul-t, they are unavoidable to be critical in the effect.
Apar-t from the aforementioned coun-termeasures, the inventors have aimed at a so-called coating rubber covering cords of a belt (hereinafter referred to as a belt coating rubber), which has never been watched in the prior art, and made various studies with respect to new solution for properties of the belt coating rubber, which is entirely different from the prior art changing the loss tangent, loss modulus and rebound resilience as previously mentioned, and as a result it has been found that the reduction of the rolling resistance can advan-tageously I 1 ~g3~3 be realized by making modulus and dynamic modulus of the belt coating rubber into appropriate values without causing - the deterioration of the wet performance as well as ride feeling against vibration, cornering stability, durability and the like.
Namely, the invention is based on the results of basic investigations with respect to the deformation state of the belt produced during the rotation of the radial tire under a certain load. ~ere, the deformation of the belt means a slip deformation (interlaminar shearing deformation) produced in the belt composed of not less than two layers, the cords of which being crossed with each other. This deformation concentrates in the vicinity of end portions of the belt to increase the internal friction loss, which has a serious influence on the rolling resistance as elucidated below.
That is, the inventors have aimed at a strain produced by the interlaminar shearing deformation of the belt and obtained such a significant knowledge that the interlaminar shearing strain of the belt i5 determined mainly b~ various dimensions such as curvature of s-urface of tire tread portion, curvature of belt, angle of cords arranged in belt, width of belt and the like and hence the belt is subjected to a substantially constant strain even when changing the properties of the belt coating rubber.
` On the basis that the strai.n of the belt is constant, theinternal energy loss due to the interlaminar shearing strain is expressed by the following equation:
EL = 2Gy2 x vol x tan ~ ............. (l) I 1~93l~3 wherein G is a static modulus or dynamic modulus ~G'), ~
is a value of strain, and tan ~ is a loss tangent related to loss modulus or rebound resilience. For this reason, the internal energy loss of the belt coating rubber can be reduced to improve the rolling resistance by lowering the static modulus G or dynamic modu~us G' of the equation (1) without the change of loss tangent, loss modulus or rebound resilience as carried out in the prior art.
As to such a knowledge, a change of the rolling resistance was actually measured by changing a modulus at 25% elongation (hereinafter referred to as 25% Mod.) and dynamic modulus of the belt coating rubber. It has been confirmed that if the index of rolling resistance is 100 in case that 25% Mod. of the belt coating rubber is 15 kg/cm2, the rolling resistance of the tire can be considerably improved to 90-80 as an index value when the belt coating rubber has 25% Mod. of 4.0-10.0 kg/cm2 and dynamic modulus of 16.2~40.5 kg/cm2.
Moreover, the dynamic modulus is a value measured at 50C, 15 Hz and an amplitude of dynamic shearing strain of 1% by means of a mechanical spectrometer (made by Rheometrix Corp).
The above-mentioned effect is led by applying the above-defined values of 25% Mod. and dynamic modulus to the belt coating rubber for at least one layer constitut-ing the belt. However, when 25% Mod. is less than 4.0 kg/cm2 and the dynamic modulus is less than 16.2 kg/cm , the belt containing cords arranged in a unidirection is too soft and the manufacture of tire becomes practically difficult.
~ccording to the invention, there is the provision of in a pneumatic radial tire comprising a body reinforce-ment including in combination of a carcass composed of at `~` 5 `; ` `
~ ~6~3~3 least one rubberized ply containing organic flber cords arranged in a substantially radial plane of the tire and wound around a bead core ~rom the inside toward the outside thereof and a belt composed of at least two rubberized layers superimposed about a crown portion o~ the carcass, each of which containing high elasticity cords inclined at a relatively small angle with respect to the circumferential direction of the tire c~nter and the cords of these layers being crossed with each other, and further comprising side-wall rubbers disposed at both sides of the carcass and a tread rubber disposed on the outer surface of the belt, the improvement wherein at least one rubberized layer constitut-ing said belt comprises a coating rubber having a modulus at 25% elongation of 4-10 ~g/cm2 and a dynamic modulus of 16.2-40.5 kg/cm .
The invention will now be described in detail with reference to the accompanying drawings, wherein:
Fig. 1 is a schematically radial half section of the tire illustrating the contribution ratio of each tire portion to rolling resistance, Fig. 2 is a graph showing a contrary relationship between index of rolling-resistance and index of wet performance for rebound resilience of tread rubber;
Figs. 3a and 3b are graphs showing influences of static and dynamic moduli of belt coating rubber ~n the rolling resistance, respectively Figs. 4a and 4b are gra~phs showing influences of sta~ic and dynamic moduli of under-tread rubber on the degree of strain concentration at belt end, respectively, Figs. 5a and 5b are graphs showing influences of static and dynamic moduli of under-tread rubber on the rolling resistance, respectively,
From the above, it is apparent that the tread rubber has a largest contribution ratio to rolling resistance.
Thexefore, in order to reduce the rolling resistance by decreasing the internal friction loss of tread rubber, it is usually performed to decrea,se loss tangent (tan ~) and ~-20 loss modulus (G") and raise rebound resilience in the rubber composition for the tread.
In this case, however, the wet performance being an important property in this type of the tire is undesirably deteriorated in accordance with the degree of improving the .:
rolling resistance. This contrary relationship is a function of rebound resilience of the tread rubber. Therefore, this .
countermeasure cannot expect the remarkable improvement of the rolling resistance unless there is taken another means for preventing the ~ .
~ ~ 2- ~
. . ,, . _, ~ ~ 6~3~3 deterioration of the wet performance. Particularly, there is found no effective means for holding the wet performance, so that the above countermeasure is not too ef~ective in - practice.
As the second countermeasure, it is attempted to apply rubber having substantially the same composition as used in the tread rubber -to sidewalls o~ the tire. In this attempt, however, the rolling resistance is practically improved only by about 3% or less, while -the damping characteristic against vibration produced in the tire is deteriorated to adversely affect the signi~icant ride feeling of the tire.
Besides, there are adopted various means for reducing the rolling resistance by weight-saving of tire, for example, by changing the carcass from two ply structure to single ply structure or by making the width of the belt narrow, but these means cause the de-teriora-tion of the cornering stability due to the reduction o~ rigidity in main reinforced portions of the tire. As a resul-t, they are unavoidable to be critical in the effect.
Apar-t from the aforementioned coun-termeasures, the inventors have aimed at a so-called coating rubber covering cords of a belt (hereinafter referred to as a belt coating rubber), which has never been watched in the prior art, and made various studies with respect to new solution for properties of the belt coating rubber, which is entirely different from the prior art changing the loss tangent, loss modulus and rebound resilience as previously mentioned, and as a result it has been found that the reduction of the rolling resistance can advan-tageously I 1 ~g3~3 be realized by making modulus and dynamic modulus of the belt coating rubber into appropriate values without causing - the deterioration of the wet performance as well as ride feeling against vibration, cornering stability, durability and the like.
Namely, the invention is based on the results of basic investigations with respect to the deformation state of the belt produced during the rotation of the radial tire under a certain load. ~ere, the deformation of the belt means a slip deformation (interlaminar shearing deformation) produced in the belt composed of not less than two layers, the cords of which being crossed with each other. This deformation concentrates in the vicinity of end portions of the belt to increase the internal friction loss, which has a serious influence on the rolling resistance as elucidated below.
That is, the inventors have aimed at a strain produced by the interlaminar shearing deformation of the belt and obtained such a significant knowledge that the interlaminar shearing strain of the belt i5 determined mainly b~ various dimensions such as curvature of s-urface of tire tread portion, curvature of belt, angle of cords arranged in belt, width of belt and the like and hence the belt is subjected to a substantially constant strain even when changing the properties of the belt coating rubber.
` On the basis that the strai.n of the belt is constant, theinternal energy loss due to the interlaminar shearing strain is expressed by the following equation:
EL = 2Gy2 x vol x tan ~ ............. (l) I 1~93l~3 wherein G is a static modulus or dynamic modulus ~G'), ~
is a value of strain, and tan ~ is a loss tangent related to loss modulus or rebound resilience. For this reason, the internal energy loss of the belt coating rubber can be reduced to improve the rolling resistance by lowering the static modulus G or dynamic modu~us G' of the equation (1) without the change of loss tangent, loss modulus or rebound resilience as carried out in the prior art.
As to such a knowledge, a change of the rolling resistance was actually measured by changing a modulus at 25% elongation (hereinafter referred to as 25% Mod.) and dynamic modulus of the belt coating rubber. It has been confirmed that if the index of rolling resistance is 100 in case that 25% Mod. of the belt coating rubber is 15 kg/cm2, the rolling resistance of the tire can be considerably improved to 90-80 as an index value when the belt coating rubber has 25% Mod. of 4.0-10.0 kg/cm2 and dynamic modulus of 16.2~40.5 kg/cm2.
Moreover, the dynamic modulus is a value measured at 50C, 15 Hz and an amplitude of dynamic shearing strain of 1% by means of a mechanical spectrometer (made by Rheometrix Corp).
The above-mentioned effect is led by applying the above-defined values of 25% Mod. and dynamic modulus to the belt coating rubber for at least one layer constitut-ing the belt. However, when 25% Mod. is less than 4.0 kg/cm2 and the dynamic modulus is less than 16.2 kg/cm , the belt containing cords arranged in a unidirection is too soft and the manufacture of tire becomes practically difficult.
~ccording to the invention, there is the provision of in a pneumatic radial tire comprising a body reinforce-ment including in combination of a carcass composed of at `~` 5 `; ` `
~ ~6~3~3 least one rubberized ply containing organic flber cords arranged in a substantially radial plane of the tire and wound around a bead core ~rom the inside toward the outside thereof and a belt composed of at least two rubberized layers superimposed about a crown portion o~ the carcass, each of which containing high elasticity cords inclined at a relatively small angle with respect to the circumferential direction of the tire c~nter and the cords of these layers being crossed with each other, and further comprising side-wall rubbers disposed at both sides of the carcass and a tread rubber disposed on the outer surface of the belt, the improvement wherein at least one rubberized layer constitut-ing said belt comprises a coating rubber having a modulus at 25% elongation of 4-10 ~g/cm2 and a dynamic modulus of 16.2-40.5 kg/cm .
The invention will now be described in detail with reference to the accompanying drawings, wherein:
Fig. 1 is a schematically radial half section of the tire illustrating the contribution ratio of each tire portion to rolling resistance, Fig. 2 is a graph showing a contrary relationship between index of rolling-resistance and index of wet performance for rebound resilience of tread rubber;
Figs. 3a and 3b are graphs showing influences of static and dynamic moduli of belt coating rubber ~n the rolling resistance, respectively Figs. 4a and 4b are gra~phs showing influences of sta~ic and dynamic moduli of under-tread rubber on the degree of strain concentration at belt end, respectively, Figs. 5a and 5b are graphs showing influences of static and dynamic moduli of under-tread rubber on the rolling resistance, respectively,
3 ~ ~
Figs. 6a and 6b are graphs showing influences of static and ~ynamic moduli of carcass coating rubber on the rolling resistance, respectively, and Fig. 7 is a schematically radial half section of an embodiment of the pneumatic radial tire according to the invention.
As illustrated in Fig. 1, conventional radial tires when operating under usual conditions, that is, including an internal pressure of 2.0 kg/cm , have a ratio of contri-buting portions to the rolling resistance as follows: treadportion, 34%; buttress portion, 27%, sidewall portion, 25%;
and bead portion, 14%. However, in conventional tires, the wet performance deteriorates proportionally with the degree of improving rolling resistance, as illustrated in Fig. 2.
This inverse relationship is a function of rebound resilience of the tread rubber. It has been found that if the modulus of elongation of the belt coating rubber is 25%, then the dynamic modulus of the belt coating rubber will result in the analysis illustrated in Figs. 3a and 3b. From the daka 2Q of Figs. 3a and 3b, it has been confirmed that if the index of rolling resistance is 100 in the case that 25% Mod. of the belt coating rubber is 15 kg/cm2, the rolling resistance of the tire can be considerably improved to 90-~0 as an index value when the belt coating rubber has 25% Mod. of
Figs. 6a and 6b are graphs showing influences of static and ~ynamic moduli of carcass coating rubber on the rolling resistance, respectively, and Fig. 7 is a schematically radial half section of an embodiment of the pneumatic radial tire according to the invention.
As illustrated in Fig. 1, conventional radial tires when operating under usual conditions, that is, including an internal pressure of 2.0 kg/cm , have a ratio of contri-buting portions to the rolling resistance as follows: treadportion, 34%; buttress portion, 27%, sidewall portion, 25%;
and bead portion, 14%. However, in conventional tires, the wet performance deteriorates proportionally with the degree of improving rolling resistance, as illustrated in Fig. 2.
This inverse relationship is a function of rebound resilience of the tread rubber. It has been found that if the modulus of elongation of the belt coating rubber is 25%, then the dynamic modulus of the belt coating rubber will result in the analysis illustrated in Figs. 3a and 3b. From the daka 2Q of Figs. 3a and 3b, it has been confirmed that if the index of rolling resistance is 100 in the case that 25% Mod. of the belt coating rubber is 15 kg/cm2, the rolling resistance of the tire can be considerably improved to 90-~0 as an index value when the belt coating rubber has 25% Mod. of
4.0-10.0 kg/cm2 and a dynamic modulus of 16.2-40.5 kg/cm2.
The invention has an essential feature that ~ 25% Mod. and dynamic modulus of the belt coating rubber ; are selected within the particular ranges of lower values as mentioned above. Therefore, if the tire is used under severe conditions, the end portion of the belt is apt to shift and finally there may be caused a fear of producing separation failure in the belt. In this case, it is -~ ~ 7 ~ ~93~3 desirable that the tread rubber is shaped into a two layer structure composed of an under-tread rubber and a top-tread rubber and also the under-tread rubber is arranged so as to completely cover the outer surface of the belt and has proper 25% Mod. and dynamic modulus.
That is, the degree of strain concentration resulted from the increase of shi~ting quantity o~ belt end portion is related to 25% Mod. or dynamic modulus of the adjoining under-tread rubber. As apparent from Figs. 4a and 4b, when 25% Mod. and dynamic modulus of the under-tread rubber are high, the degree of strain concentration at .
-~:
~' :
1 ~6~3~3 belt end expressed by a ratio of strain a-t belt end to strain at portion sufficiently separated from belt end becomes high, while when 25% Mod. and dy~amic modulus of the under-tread rubber are low, the degree of strain concentration at belt end is advantageously mitigated.
In this connection, when the belt coating rubber has 25% Mod. of 8.0 kg/cm2 and dynamic modulus of 32.9 kg/cm2, the durability to separation failure is measured with respect to tires A, B and C running on a drum under high internal pressure and high load, wherein the tire A com-prises an under-tread rubber having 25% Mod. of 9.0 kg/cm2 (dynamic modulus of 37.4 kg/cm2) as a control tire, the tire B comprises an under-tread rubber having 25% Mod. of 8 kg/cm2 (dynamic modulus of 32.9 kg/cm2) and the tire C
comprises an under--tread rubber having 25% Mod. of 3 kg/cm2 (dynamic modul-us of 13 kg/cm2), to obtain a result as shown in the following Table 1, which is expressed by an index on the basis that a tire having the same values of 25% Mod. and dynamic modulus of the belt coating rubber and under-tread rubber as in the prior art is lO0.
- The larger the index value, the better the durability.
~: :
Table 1 Belt coating Under-tread Tire rubber rubber Durability 25% Mod. 25% Mod.
A 8.0 9.0 75 B 8.0 8.0 85 _ ___ C 8.0 3.0 98 Il 3 ~3~ 3 As apparent from the data of Table 1, when 25% ~od. and dynamic modulus of the belt coa-ting rubber are merely lowered, the durability is deteriorated up to 75 as an index value under severe conditions, which can sufficiently be solved by further lowering 25% Mod. and dynamic modulus of the under-tread rubber.
As described above, according to the invention, the deterioration of durability can be prevented by giving appropriate properties to the under-tread rubber adjacen-t to the outer surface of the belt. Furthermore, the improve-ment of durability can be more expected by giving proper values of 25% Mod. and dynamic modulus to a coating rubber for the carcass ply (hereinafter referred to as a carcass coating rubber~ adjacent to the inner surface of -the belt on the same reason as mentionecl above.
The following Table 2 shows results of durability measured under the same condition as described on Table 1 with respect to the tire C of Table 1 and tires C-l and C-2, wherein the tire C comprises a carcass coating rubber having 25% Mod. of 9.3 kg/cm2 and dynamic modulus o-f 38.2 kg/cm2, the tire C-l comprises a carcass coating rubber having 25% Mod. of 6.0 kg/cm2 (dynamic modulus of 20.4 kg/cm2) and the tire C-2 comprises a carcass coating rubber having 25% Mod. of 3.0 kgjcm2 (dynamic modulus of 13.0 kg/cm2).
3 4 ~ ;
Table 2 Belt coating Under-tread Carcass coat-Tire rubber rubber ing rubber Durability 25% Mod. 25% Mod. 25% Mod.
C 8.0 3.0 9.3 98 C-l 8.0 3.0 6.0 105 C-2 ~.0 3.0 3.0 110 As apparent from Table 2, the durability can further be improved by lowering 25% Mod. and dynamic modulus of each of the under-tread rubber and carcass coating rubber, which is a preferable embodiment of the 15invention.
Then, the feature of selecting 25% Mod. and dynamic modulus of the under-tread rubber and carcass coating rubber within particular ranges of lower values will be described with respect to the influence on rolling resistance aimed at the invention. In conclusion, the inventors have analyzed the deformation states of -the tread and sidewall portions when -the radial tire was - rotated under a load and found that these analytical results are effective for the improvemen-t of rolling resistance and attain the rapid improvement of ro]lin~
resistance together with the decrease of 25% Mod. and - dynamic modulus of the bel-t coating rubber.
At first, the inventors have made studies with respect to the deformation of the tread portion and found that there is a difference in the deforma-tion state between : , .
~ ~9~43 a portion near the tread surface and a portion adjacent to a bel-t. Tha-t is, the former de~ormation is determined by - a force transmitted between the -tire and the road surface, while the latter deformation is controlled by transmit-ting a deformation of the belt as a shearing strain. Particu-larly, aiming at the latter deformation and considering that the deformation of the belt is substantially determined by a tension or rigidity of the belt, it is understood that the shearing strain applied to -the under-tread rubber adjacent to the belt is approxima-tely constant irrespective of its properties. On the basis that the shearing strain is CQnStant, it is apparent tha-t the internal energy loss can be reduced to improve -the rolling resistance by making 25% Mod. and dynamic modulus of the under-tread rubber into appropriate values likewise the case of the belt coating rubber. In Figs. 5a and 5'b are shown results for - the rolling resistance measured by actually changing 25% Mod. and dynamic modulus of the ~lnder--tread rubber, respec-tively. As apparent from these resul-ts, when the under-tread rubber has 25% Mod. of 2-8 kg/cm2 and dynamic modulus of 8.2-33.0 kg/cm2, the reduction of the rolling resistance to 93-85 as an index value can advantageously ; be achieved. Conveniently, such ranges of 25% Mod. and dynamic modulus are consistent with the ranges for the improvement of durability as previously mentioned.
Next, the invention will be described with respect -to the deformation of the sidewall por-tion. Here~
the deformation of the si,dewall portion means to include a bending deformation produced on the outside of the sidewall portion and a shearing deformation produced .
- ~ ~
1 3 ~3~ 3 inside the sidewall portion. Particularly 7 the shearing deformation become~ imp~rtant becawse it is small in the ground contact area just beneath the rotational axis of the tire but occupies 75% of total deformation of the sidewall portion in the entering and departing areas near the ground contact area. Now, the inventors have fwr-ther aimed at a strain produced by the shearing deformation and got a significant knowledge as described below. That is, the distribution of the shearing strain in the thickness direction of the sidewall portion is maximum in the vicinity of the carcass ply cord and the shearing deformation of the sidewall portion is substantially determined by the tension of the carcass ply, so that the shearing strain of rubber arranged in the sidewall portion is approximately constant irrespective of its properties. On the basis of this fact, the same effect as in the bel-t coating rubber - can be developed by applying the aforemen-tioned thought to ~i the carcass coating rubber. In other words, the rollin~
resistance can be improved by lowering the static modullls G or dynamic modulus G' of the carcass coating rubber according to -the equation (1). Really, a change of the rolling resistance was measured by changing 25% Mod. and dynamic modulus of the carcass coating rubber to obtain results as shown in Figs. 6a and 6b. From the data of Figs. 6a and 6b, it has been confirmed that if the index of rolling resistance is 100 in case that 25% Mod. of the carcass coating rubber is 9.3 kg/cm2, -the rolling resistance of the tire can considerably be improved to 80-90 as an index value when the carcass coating rubber has 25% Mod.
of 2-6 kg/cm2, preferably 3-5 kg/cm2. In this connection, .
} ~ 3 ~ 3 the dynamic modulus of the carcass coa~ting rubber is 8.2-20.4 kg/cm2, preferably 12.5-19.0 kg/cm2. Of course, these ranges of 25% Mod. and dynamic modulus of the carcass coating rubber are included in the ranges used for the improvement of durability shown in Table 1.
In order to confirm the concrete effect of the invention, the following tests were made with respect to a tire having a size of 185/70 SR 14 as shown in Fig. 7, wherein reference numeral 1 is a top-tread rubber, reference numeral 2 an under-tread rubber, reference numeral 3 a belt, reference numeral 4 a carcass, reference numeral 5 a sidewall portion and reference numeral 6 a bead core.
At first, a control -tire was prepared by using a belt coating rubber having 25% ~Mod. of 15 kg/cm2 and dynamic modulus of 59 kg/cm2 J an under-tread rubber having 25% Mod. of 9 kg/cm2 and dynamic modulus of 37.4 kg/cm2 .~ and a carcass coating rubber having 25% Mod. of 9.3 kg/cm2 and dynamic modulus of 38.2 kg/cm2 and there were provided tires D-F according to the invention having the same size, structure and rubber properties as in the control tire except that 25% Mod. and dynam]c modulus of the rubber ` shown in the following Table 3. Then, the rolling resist-ances of the control tire and tires D-F were measured a-t running speeds of 50, 80 and 100 km~hr to obtain results as shown in Table 3, wherein -the imprvvement of the rolling resistance is expressed by an index on the basis that the control tire is 100 and the smaller the index value, the better the improvement of the rolling resistance.
' ' ~ . ' '~
1 1 ~93ll3 Table 3 rCti~e1 Tire D Tire E Tire F
Belt coating rubber 25% Mod. (kg/cm2~ 15 8.0 8.0 8.0 Dynamic modulus (kg/cm2) 59 32.9 32.9 32.9 Under-tread rubber 25% Mod. (kg/cm2) 9 9 6.5 6.5 Dynamic modulus (kg/cm2) 37.4 37.4 26.0 26.0 Carcass coating rubber 25% Mod. (kg/cm2) 9.3 9.3 9.3 6.0 Dynamic modulus (kg/cm2) 38.2 38.2 38.2 20.4 Index of rolling resistance at a given running speed 50 km/hr lO0 88 80 70 ~, 80 km/hr 100 90 82 72 100 km/hr 100 92 85 75 The test for rolling resistance was performed as follows: that is, the tire was rota-ted on a drum having a diameter of 1,707 mm by the driving of a motor, and thereafter the driving of the motor was stopped to run the drum by inertia, during which the rolling resistance was measured from the degree of deceleration speed. In this case, the internal pressure was 1.7 kg/cm2 and the load was 445 kg.
Then~ the test for wet performance on concrete road surface ~SN indicating the degree of roughness of road surface = 35) or asphalt road surface (SN=50) was made with respec-t to the control tire and tire F. As a result, there was observed no difference in the wet performance between both the tires.
Next, each of the control tire and tire F was placed on a drum provided with a protrusion and then run at a low or high rotating speed, during which a force produced on the rotational axis of the tire was measured for evaluation of ride feeling against vibration to obtain results as shown in the following Table 4, wherein the ride feeling against vibration is expressed by an index on the basis that the control tire is 100 and the larger the index value, the better the property.
Table 4 Running Control Tire F
- condition tire Reaction force in up and low speed area 100 lG5 ~ down direction when _ _ ::. riding on protrusion high speed area 100 99 Reaction force in front low speed area 100 100 and rear direction when _ _ ; riding on protrusion high speed area 100 103 '' As apparent from the data of Table 4, the ride feeling against vibration of the tire F according to the invention is not substantially deteriorated or is somewhat improved to that of the control tire.
`~ Furthermore, the control tire and tire F were measured with respect to the cornering power as a cornering stabili~y. When the cornering stability of the control tire is 100 as an index value 3 the cornering stability of ~ 3 ~3~1 3 the tire F is approximately 99 as an index value.
Finally, when the tire F according -to -the inven-- tion was run on a drum under higher internal pressure and higher load, it has been confirmed that the durability under such severe conditions is improved to 105 as an index ' value when the control tire is lO0.
As mentioned above, ~he invention selects the properties o~ the belt coating rubber from the particular ranges, which have never been noticed 'in the prior art, whereby the rolling resistance of the tire can considerably be improved without causing the deterloration of wet ' performance, ride feeling against vibration, cornering stability, durability and the like.
` 15 - ~0
The invention has an essential feature that ~ 25% Mod. and dynamic modulus of the belt coating rubber ; are selected within the particular ranges of lower values as mentioned above. Therefore, if the tire is used under severe conditions, the end portion of the belt is apt to shift and finally there may be caused a fear of producing separation failure in the belt. In this case, it is -~ ~ 7 ~ ~93~3 desirable that the tread rubber is shaped into a two layer structure composed of an under-tread rubber and a top-tread rubber and also the under-tread rubber is arranged so as to completely cover the outer surface of the belt and has proper 25% Mod. and dynamic modulus.
That is, the degree of strain concentration resulted from the increase of shi~ting quantity o~ belt end portion is related to 25% Mod. or dynamic modulus of the adjoining under-tread rubber. As apparent from Figs. 4a and 4b, when 25% Mod. and dynamic modulus of the under-tread rubber are high, the degree of strain concentration at .
-~:
~' :
1 ~6~3~3 belt end expressed by a ratio of strain a-t belt end to strain at portion sufficiently separated from belt end becomes high, while when 25% Mod. and dy~amic modulus of the under-tread rubber are low, the degree of strain concentration at belt end is advantageously mitigated.
In this connection, when the belt coating rubber has 25% Mod. of 8.0 kg/cm2 and dynamic modulus of 32.9 kg/cm2, the durability to separation failure is measured with respect to tires A, B and C running on a drum under high internal pressure and high load, wherein the tire A com-prises an under-tread rubber having 25% Mod. of 9.0 kg/cm2 (dynamic modulus of 37.4 kg/cm2) as a control tire, the tire B comprises an under-tread rubber having 25% Mod. of 8 kg/cm2 (dynamic modulus of 32.9 kg/cm2) and the tire C
comprises an under--tread rubber having 25% Mod. of 3 kg/cm2 (dynamic modul-us of 13 kg/cm2), to obtain a result as shown in the following Table 1, which is expressed by an index on the basis that a tire having the same values of 25% Mod. and dynamic modulus of the belt coating rubber and under-tread rubber as in the prior art is lO0.
- The larger the index value, the better the durability.
~: :
Table 1 Belt coating Under-tread Tire rubber rubber Durability 25% Mod. 25% Mod.
A 8.0 9.0 75 B 8.0 8.0 85 _ ___ C 8.0 3.0 98 Il 3 ~3~ 3 As apparent from the data of Table 1, when 25% ~od. and dynamic modulus of the belt coa-ting rubber are merely lowered, the durability is deteriorated up to 75 as an index value under severe conditions, which can sufficiently be solved by further lowering 25% Mod. and dynamic modulus of the under-tread rubber.
As described above, according to the invention, the deterioration of durability can be prevented by giving appropriate properties to the under-tread rubber adjacen-t to the outer surface of the belt. Furthermore, the improve-ment of durability can be more expected by giving proper values of 25% Mod. and dynamic modulus to a coating rubber for the carcass ply (hereinafter referred to as a carcass coating rubber~ adjacent to the inner surface of -the belt on the same reason as mentionecl above.
The following Table 2 shows results of durability measured under the same condition as described on Table 1 with respect to the tire C of Table 1 and tires C-l and C-2, wherein the tire C comprises a carcass coating rubber having 25% Mod. of 9.3 kg/cm2 and dynamic modulus o-f 38.2 kg/cm2, the tire C-l comprises a carcass coating rubber having 25% Mod. of 6.0 kg/cm2 (dynamic modulus of 20.4 kg/cm2) and the tire C-2 comprises a carcass coating rubber having 25% Mod. of 3.0 kgjcm2 (dynamic modulus of 13.0 kg/cm2).
3 4 ~ ;
Table 2 Belt coating Under-tread Carcass coat-Tire rubber rubber ing rubber Durability 25% Mod. 25% Mod. 25% Mod.
C 8.0 3.0 9.3 98 C-l 8.0 3.0 6.0 105 C-2 ~.0 3.0 3.0 110 As apparent from Table 2, the durability can further be improved by lowering 25% Mod. and dynamic modulus of each of the under-tread rubber and carcass coating rubber, which is a preferable embodiment of the 15invention.
Then, the feature of selecting 25% Mod. and dynamic modulus of the under-tread rubber and carcass coating rubber within particular ranges of lower values will be described with respect to the influence on rolling resistance aimed at the invention. In conclusion, the inventors have analyzed the deformation states of -the tread and sidewall portions when -the radial tire was - rotated under a load and found that these analytical results are effective for the improvemen-t of rolling resistance and attain the rapid improvement of ro]lin~
resistance together with the decrease of 25% Mod. and - dynamic modulus of the bel-t coating rubber.
At first, the inventors have made studies with respect to the deformation of the tread portion and found that there is a difference in the deforma-tion state between : , .
~ ~9~43 a portion near the tread surface and a portion adjacent to a bel-t. Tha-t is, the former de~ormation is determined by - a force transmitted between the -tire and the road surface, while the latter deformation is controlled by transmit-ting a deformation of the belt as a shearing strain. Particu-larly, aiming at the latter deformation and considering that the deformation of the belt is substantially determined by a tension or rigidity of the belt, it is understood that the shearing strain applied to -the under-tread rubber adjacent to the belt is approxima-tely constant irrespective of its properties. On the basis that the shearing strain is CQnStant, it is apparent tha-t the internal energy loss can be reduced to improve -the rolling resistance by making 25% Mod. and dynamic modulus of the under-tread rubber into appropriate values likewise the case of the belt coating rubber. In Figs. 5a and 5'b are shown results for - the rolling resistance measured by actually changing 25% Mod. and dynamic modulus of the ~lnder--tread rubber, respec-tively. As apparent from these resul-ts, when the under-tread rubber has 25% Mod. of 2-8 kg/cm2 and dynamic modulus of 8.2-33.0 kg/cm2, the reduction of the rolling resistance to 93-85 as an index value can advantageously ; be achieved. Conveniently, such ranges of 25% Mod. and dynamic modulus are consistent with the ranges for the improvement of durability as previously mentioned.
Next, the invention will be described with respect -to the deformation of the sidewall por-tion. Here~
the deformation of the si,dewall portion means to include a bending deformation produced on the outside of the sidewall portion and a shearing deformation produced .
- ~ ~
1 3 ~3~ 3 inside the sidewall portion. Particularly 7 the shearing deformation become~ imp~rtant becawse it is small in the ground contact area just beneath the rotational axis of the tire but occupies 75% of total deformation of the sidewall portion in the entering and departing areas near the ground contact area. Now, the inventors have fwr-ther aimed at a strain produced by the shearing deformation and got a significant knowledge as described below. That is, the distribution of the shearing strain in the thickness direction of the sidewall portion is maximum in the vicinity of the carcass ply cord and the shearing deformation of the sidewall portion is substantially determined by the tension of the carcass ply, so that the shearing strain of rubber arranged in the sidewall portion is approximately constant irrespective of its properties. On the basis of this fact, the same effect as in the bel-t coating rubber - can be developed by applying the aforemen-tioned thought to ~i the carcass coating rubber. In other words, the rollin~
resistance can be improved by lowering the static modullls G or dynamic modulus G' of the carcass coating rubber according to -the equation (1). Really, a change of the rolling resistance was measured by changing 25% Mod. and dynamic modulus of the carcass coating rubber to obtain results as shown in Figs. 6a and 6b. From the data of Figs. 6a and 6b, it has been confirmed that if the index of rolling resistance is 100 in case that 25% Mod. of the carcass coating rubber is 9.3 kg/cm2, -the rolling resistance of the tire can considerably be improved to 80-90 as an index value when the carcass coating rubber has 25% Mod.
of 2-6 kg/cm2, preferably 3-5 kg/cm2. In this connection, .
} ~ 3 ~ 3 the dynamic modulus of the carcass coa~ting rubber is 8.2-20.4 kg/cm2, preferably 12.5-19.0 kg/cm2. Of course, these ranges of 25% Mod. and dynamic modulus of the carcass coating rubber are included in the ranges used for the improvement of durability shown in Table 1.
In order to confirm the concrete effect of the invention, the following tests were made with respect to a tire having a size of 185/70 SR 14 as shown in Fig. 7, wherein reference numeral 1 is a top-tread rubber, reference numeral 2 an under-tread rubber, reference numeral 3 a belt, reference numeral 4 a carcass, reference numeral 5 a sidewall portion and reference numeral 6 a bead core.
At first, a control -tire was prepared by using a belt coating rubber having 25% ~Mod. of 15 kg/cm2 and dynamic modulus of 59 kg/cm2 J an under-tread rubber having 25% Mod. of 9 kg/cm2 and dynamic modulus of 37.4 kg/cm2 .~ and a carcass coating rubber having 25% Mod. of 9.3 kg/cm2 and dynamic modulus of 38.2 kg/cm2 and there were provided tires D-F according to the invention having the same size, structure and rubber properties as in the control tire except that 25% Mod. and dynam]c modulus of the rubber ` shown in the following Table 3. Then, the rolling resist-ances of the control tire and tires D-F were measured a-t running speeds of 50, 80 and 100 km~hr to obtain results as shown in Table 3, wherein -the imprvvement of the rolling resistance is expressed by an index on the basis that the control tire is 100 and the smaller the index value, the better the improvement of the rolling resistance.
' ' ~ . ' '~
1 1 ~93ll3 Table 3 rCti~e1 Tire D Tire E Tire F
Belt coating rubber 25% Mod. (kg/cm2~ 15 8.0 8.0 8.0 Dynamic modulus (kg/cm2) 59 32.9 32.9 32.9 Under-tread rubber 25% Mod. (kg/cm2) 9 9 6.5 6.5 Dynamic modulus (kg/cm2) 37.4 37.4 26.0 26.0 Carcass coating rubber 25% Mod. (kg/cm2) 9.3 9.3 9.3 6.0 Dynamic modulus (kg/cm2) 38.2 38.2 38.2 20.4 Index of rolling resistance at a given running speed 50 km/hr lO0 88 80 70 ~, 80 km/hr 100 90 82 72 100 km/hr 100 92 85 75 The test for rolling resistance was performed as follows: that is, the tire was rota-ted on a drum having a diameter of 1,707 mm by the driving of a motor, and thereafter the driving of the motor was stopped to run the drum by inertia, during which the rolling resistance was measured from the degree of deceleration speed. In this case, the internal pressure was 1.7 kg/cm2 and the load was 445 kg.
Then~ the test for wet performance on concrete road surface ~SN indicating the degree of roughness of road surface = 35) or asphalt road surface (SN=50) was made with respec-t to the control tire and tire F. As a result, there was observed no difference in the wet performance between both the tires.
Next, each of the control tire and tire F was placed on a drum provided with a protrusion and then run at a low or high rotating speed, during which a force produced on the rotational axis of the tire was measured for evaluation of ride feeling against vibration to obtain results as shown in the following Table 4, wherein the ride feeling against vibration is expressed by an index on the basis that the control tire is 100 and the larger the index value, the better the property.
Table 4 Running Control Tire F
- condition tire Reaction force in up and low speed area 100 lG5 ~ down direction when _ _ ::. riding on protrusion high speed area 100 99 Reaction force in front low speed area 100 100 and rear direction when _ _ ; riding on protrusion high speed area 100 103 '' As apparent from the data of Table 4, the ride feeling against vibration of the tire F according to the invention is not substantially deteriorated or is somewhat improved to that of the control tire.
`~ Furthermore, the control tire and tire F were measured with respect to the cornering power as a cornering stabili~y. When the cornering stability of the control tire is 100 as an index value 3 the cornering stability of ~ 3 ~3~1 3 the tire F is approximately 99 as an index value.
Finally, when the tire F according -to -the inven-- tion was run on a drum under higher internal pressure and higher load, it has been confirmed that the durability under such severe conditions is improved to 105 as an index ' value when the control tire is lO0.
As mentioned above, ~he invention selects the properties o~ the belt coating rubber from the particular ranges, which have never been noticed 'in the prior art, whereby the rolling resistance of the tire can considerably be improved without causing the deterloration of wet ' performance, ride feeling against vibration, cornering stability, durability and the like.
` 15 - ~0
Claims (4)
1. In a pneumatic radial tire comprising a body reinforcement including in combination of a carcass composed of at least one rubberized ply containing organic fiber cords arranged in a substantially radial plane of the tire and wound around a bead core from the inside toward the outside thereof and a belt composed of at least two rubberized layers superimposed about a crown portion of the carcass, each of which containing high elasticity cords inclined at a relatively small angle with respect to the circumferential direction of the tire center and the cords of these layers being crossed with each other) and further comprising sidewall rubbers disposed at both sides of the carcass and a tread rubber disposed on the outer surface of the belt, the improvement wherein at least one rubberized layer constituting said belt comprises a coating rubber having a modulus at 25% elongation of 4-10 kg/cm2 and a dynamic modulus of 16.2-40.5 kg/cm2.
2. The pneumatic radial tire according to claim 1, wherein said tread rubber has a two layer structure composed of an under-tread rubber completely covering the outer surface of the belt and a top-tread rubber superimposed thereabout.
3. The pneumatic radial tire according to claim 2, wherein said under-tread rubber has a modulus at 25%
elongation of 2.0-8.0 kg/cm2 and a dynamic modulus of 8.2-33.0 kg/cm2.
elongation of 2.0-8.0 kg/cm2 and a dynamic modulus of 8.2-33.0 kg/cm2.
4. The pneumatic radial tire according to claim 1 or 3, wherein a coating rubber for said carcass has a modulus at 25% elongation of 2.0-6.0 kg/cm2 and a dynamic modulus of 8.2-20.4 kg/cm2.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP56115351A JPS5816904A (en) | 1981-07-24 | 1981-07-24 | Pneumatic radial tire |
| JP115,351/81 | 1981-07-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1169343A true CA1169343A (en) | 1984-06-19 |
Family
ID=14660368
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000407838A Expired CA1169343A (en) | 1981-07-24 | 1982-07-22 | Pneumatic radial tires |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5816904A (en) |
| CA (1) | CA1169343A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5226987A (en) * | 1988-07-27 | 1993-07-13 | Toyo Tire & Rubber Company Limited | Radial tire for heavy load vehicles including a rubber reinforcing layer between belt and tread |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7150301B2 (en) * | 2000-05-30 | 2006-12-19 | Pirelli Pneumatici S.P.A. | Motor vehicle tire with low rolling resistance |
| JP5881438B2 (en) * | 2012-01-30 | 2016-03-09 | 東洋ゴム工業株式会社 | Pneumatic tire |
-
1981
- 1981-07-24 JP JP56115351A patent/JPS5816904A/en active Pending
-
1982
- 1982-07-22 CA CA000407838A patent/CA1169343A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5226987A (en) * | 1988-07-27 | 1993-07-13 | Toyo Tire & Rubber Company Limited | Radial tire for heavy load vehicles including a rubber reinforcing layer between belt and tread |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5816904A (en) | 1983-01-31 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4349061A (en) | Pneumatic radial tires for passenger cars having a low rolling resistance | |
| US5164028A (en) | Radial tire | |
| EP0719662B1 (en) | Pneumatic tyre | |
| EP0715977B1 (en) | Pneumatic radial tires | |
| US4407346A (en) | Pneumatic tire for motor vehicles having a low power absorption and a high directional control stability | |
| US5479977A (en) | Pneumatic tire with carcass structure for increased sidewall rigidity | |
| US5200006A (en) | Pneumatic tire with uniform ground pressure at the tread face | |
| EP0620131B1 (en) | Radial tyre for a motor cycle | |
| EP0890452B1 (en) | Pneumatic tyre | |
| JPH02185802A (en) | Pneumatic radial tire | |
| EP0736400B1 (en) | Heavy duty pneumatic radial tires | |
| EP0712738B1 (en) | Pneumatic radial tyre | |
| US5240057A (en) | High performance pneumatic radial tires with auxiliary belt layers | |
| JPH0672104A (en) | Pneumatic radial tire | |
| JPS63141809A (en) | Pneumatic tire | |
| EP1199192B1 (en) | Pneumatic tire | |
| EP1366930B1 (en) | Heavy duty pneumatic radial tires | |
| EP0953463B1 (en) | Pneumatic tires | |
| US4757850A (en) | Tire for motorcycles | |
| JPH03204307A (en) | Radial tire for passenger car | |
| CA1169343A (en) | Pneumatic radial tires | |
| EP0810105B1 (en) | Pneumatic radial tires provided with a side portion reinforcing layer | |
| EP2300245B1 (en) | Motorcycle tire | |
| CA1170556A (en) | Pneumatic radial tire | |
| CA1169344A (en) | Pneumatic radial tires for passenger cars used under high internal pressure |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |