Patent Application
20220048340
The present invention relates to a pneumatic tire, and more specifically, to a pneumatic tire that achieves both ride comfort and steering stability at a high level.
In the structure of pneumatic tires, there is often a conflict between improving ride comfort and improving steering stability, and research and development are being conducted to find a balance between ride comfort and steering stability. There is a pneumatic radial tire in which a reinforcing layer composed of fiber cords or steel cords is arranged around the entire circumference of the tire from a bead portion to a sidewall portion, and the cord angle of the reinforcing layer is almost perpendicular to a carcass cord of a carcass layer (Patent Document 1). There is a pneumatic radial tire in which a bead reinforcing layer is divided into two layers, inner and outer, and the circumferential ply rigidity of the outer layer near the center of a sidewall is larger than that of the inner layer near a bead core (Patent Document 2).
However, both of the pneumatic radial tires described in Patent Document 1 and Patent Document 2 have an excessively strong elongation constraint against an input to cords of a bead reinforcement layer caused by bending deformation of a sidewall portion during straight running, resulting in a high vertical spring coefficient of the tire, which deteriorates the ride comfort.
Accordingly, an object of the present invention is to provide a pneumatic tire that achieves both ride comfort and steering stability at a high level.
The pneumatic tire of the present invention is a pneumatic tire including: a pair of bead portions each containing a bead core, a pair of sidewall portions each connected to each of the pair of bead portions and extending outward in a radial direction, and a tread portion connecting the outer circumferential edges of the pair of sidewall portions; as well as
a carcass arranged in such a manner that both ends thereof are each folded over the bead core in the pair of bead portions to form a toroidal shape from the sidewall portions to the tread portion; a belt provided on the outer circumferential side of a crown portion of the carcass; the bead core provided between a main body portion and a folding-over portion of the carcass in the bead portion; and
a cord provided in at least one part from the bead portion to the sidewall portions at an angle of 0 to 10° with respect to the circumferential direction, wherein
the bead core has a ratio of the maximum width of the core to the height of the core of 0.8 or less in a cross-section in the tire width direction, and
the cord has an inflection point in a stress-strain curve, with a low elastic modulus in a low-strain region at or below the inflection point, and a high elastic modulus in a high-strain region above the inflection point.
In such a pneumatic tire, the maximum width of a bead core is smaller than values obtained in relation to the bead core height, allowing the size of a bead filler to be reduced and the weight of the tire to be reduced. Reinforcement using a cord with low elastic modulus in a low-strain region at or below an inflection point and high elastic modulus in a high-strain region above the inflection point suppresses an increase in rigidity in a low elastic modulus region for vertical rigidity, which is related to the ride comfort, while high rigidity is obtained in a high elastic modulus region for lateral rigidity, which is related to the steering stability, thus achieving both ride comfort and steering stability at a high level.
In the pneumatic tire of the present invention, the bead core preferably has a ratio of the width of an outer portion of the core in the radial direction to the height of the core of 0.7 or less.
The cord may be composed of two or more kinds of fibers of different materials, and the fibers may be composed of organic fibers or inorganic fibers.
The cord may be arranged between the main body portion ply of the carcass and the bead filler, between the bead filler and a folding-over portion ply of the carcass, or outside the folding-over portion ply of the carcass in the tire radial direction.
Furthermore, the material of the cord preferably contains at least aramid or polyethylene terephthalate.
Still furthermore, the cord preferably has the inflection point in the range of 1 to 8% tensile strain, and the elastic modulus in the low-strain region is in the range of 10 to 90% of the elastic modulus in the high-strain region.
The method of manufacturing pneumatic tires of the present invention is a method of manufacturing the above-described pneumatic tire, wherein
one or more kinds of non-linear elastic modulus cords having a non-linear elastic modulus are prepared, the elastic moduli of the non-linear elastic modulus cords are controlled in a tire molding process by applying different tensions to the non-linear elastic modulus cords depending on the position of the cords in the tire, and non-linear elastic modulus cords of more kinds than the prepared non-linear elastic modulus cords are formed in the tire.
According to the present invention, both ride comfort and steering stability can be achieved at a high level.
Embodiments of the pneumatic tire of the present invention (hereinafter, also simply referred to as “tire”) will be described in more detail using the drawings.
The carcass 7 has a toroidal shape extending from the pair of sidewall portions 3 connected to the pair of bead portions 2 to the tread portion 4. The carcass 7 is composed of a carcass ply obtained by coating a carcass cord with rubber, and serves as a framework to maintain the shape of the pneumatic tire 1. In radial tires, the carcass cord of the carcass 7 extends in the tire radial direction.
A belt 8 composed of one or more belt plies is arranged on the outer circumferential side of the crown portion of the carcass 7.
In the pneumatic tire of the present invention, the bead core 5 has a ratio of the maximum width of the core to the height of the core of 0.8 or less in a cross-section in the tire width direction. This bead core 5 will be described in more detail.
Pneumatic tires are needed to be lighter in order to reduce the unsprung weight of automobiles, and for this purpose, bead cores and bead fillers are considered to be made smaller. The bead core is an assembly of a plurality of bead wires, and if the cross-sectional area of the bead core is simply reduced, the pressure resistance performance will be degraded, and therefore a minimum necessary cross-sectional area must be secured. When a bead filler is made thinner and smaller for a bead core with such a predetermined cross-sectional area, a tire can be made lighter. However, when a bead filler and a bead core do not connect smoothly, a main body portion and a folding-over portion of a carcass ply do not connect smoothly. Considering thinning of the bead filler or smooth connection between the bead core and the bead filler as described above, it is preferable to make the bead core shorter in the tire width direction and longer in the tire radial direction in accordance with thinning of the bead filler.
Repeated research on a preferable relationship between the maximum width of the bead core in the tire width direction and the height of the bead core in the tire radial direction revealed that the weight of the tire, including the bead filler, can be reduced when the ratio of the maximum width of the core to the height of the core is 0.8 or less.
In order for a bead core and a bead filler to be smoothly connected, it is preferable that the width of the bead filler on the inner side in the tire radial direction and the width of the bead core on the outer side in the tire radial direction opposite the inner side in the tire radial direction of the bead filler should be almost the same, and that the width of the bead core on the outer side in the tire radial direction is narrower than the maximum width of the bead core. Therefore, when the ratio of the width of an outer portion of the bead core in the radial direction to the height of the core is 0.7 or less, together with the above-described relationship of the ratio of the maximum width of the core to the height of the core is 0.8 or less, the tire weight of the tire, including the bead filler, can be reduced.
As understood from
By optimizing dimensions of a bead core and reducing the thickness of a bead filler, both the vertical spring coefficient and the lateral spring coefficient of a tire are lowered, which improves the ride comfort, but may reduce the steering stability. The pneumatic tire 1 of the present invention can address this problem with cords 9, since the cords 9 are provided in at least one part from a bead portion 2 to a sidewall portion 3. The cords 9 will be described in detail below.
As illustrated in the cross-sectional view in
In the present embodiment illustrated in
An operational advantage of the cords 9 will be described using
A deformed state of the tire 1 when loaded, viewed in a vertical cross section including the tire rotation axis, is illustrated in
In
A deformed state of the tire 1 when loaded during cornering, viewed in a vertical cross section including the tire rotation axis, is illustrated in
An effect of the non-linear elastic modulus cord 9, which is at an angle of 0 to 10° with respect to the circumferential direction, provided in the pneumatic tire of the present embodiment on the tire deformation during straight running illustrated in
First, a case of a comparative tire with reinforcing cords in at least one part from a bead portion to a sidewall portion at an angle greater than 10° with respect to the circumferential direction will be described.
When, as in the comparative tire, a cord with a large angle to the circumferential direction is provided in a bead portion, the cord, which has more rigidity than rubber, is strained against a force of bending deformation of the bead portion in a cross section in the tire width direction. Therefore, the cords exhibit a rigidity that suppresses tire deformation, in particular bending deformation of the bead portion. Therefore, such a comparative tire has a larger vertical spring coefficient (spring constant in the tire radial direction), or in other words, the tire has a higher vertical rigidity, which worsens the ride comfort. When the cord suppresses bending deformation of a bead portion, not only is a vertical (tire radial) deformation suppressed, but a lateral (tire width) deformation is also suppressed. Therefore, the lateral spring coefficient (spring constant in the tire width direction) of the tire is increased, in other words, the lateral rigidity is increased and the steering stability is improved.
Next, a case of a comparative tire with reinforcing cords, which are cords with a small angle with respect to the circumferential direction (from 0 to 10° with respect to the circumferential direction) but are not non-linear elastic modulus cords, provided in at least one part from a bead portion to a sidewall portion will be described.
When a cord with a small angle with respect to the circumferential direction is provided in a bead portion, as in such a comparative tire, there is no effect of the cord on a force of bending deformation of the bead portion in a cross section in the tire width direction during straight running, since rubber between the cords, which has a low elastic modulus, stretches and deforms. In response to a force of bulging deformation in a sidewall portion, a strain is applied to the cord at an angle close to the circumferential direction, which has a high elastic modulus, and this cord is difficult to stretch, and the rigidity of the tire is thus increased. Therefore, the vertical spring coefficient of such a comparative tire is not affected by the cords in the bead portion, but is affected by the cords in the sidewall portion, and the coefficient becomes larger.
A case of this comparative tire during cornering will be described. When cords with a small angle with respect to the circumferential direction are provided in at least one part from the bead portion to the sidewall portion, a force of bending deformation of the bead portion in a cross section in the tire width direction has no effect since rubber between the cords, which has a low elastic modulus, stretches and deforms. Regarding a force of bulging deformation of the sidewall portions, the portion of the sidewall portion outside the cornering where the bulging deformation is reduced among the pair of sidewall portions, is not affected by the cords since no force is applied to the cords due to the reduced bulging deformation, although the cords with an angle close to the circumferential direction, which have a high elastic modulus, are provided. In a portion of the sidewall portion inside the cornering where bulging increases, a strain is applied to the cords at an angle close to the circumferential direction, which have a high elastic modulus, and since these cords are difficult to stretch, the tire rigidity can be increased. Accordingly, the inventors' research newly found that the lateral spring coefficient of the tire increases due to the influence of the cords inside the cornering, although not influenced by the cords of the bead portion and the cords outside the cornering.
The vertical spring coefficient of a tire during straight running influences ride comfort, while the lateral spring coefficient of a tire during cornering influences steering stability. Therefore, it was found that, in order to improve the ride comfort by reducing an increase in the vertical spring of the tire during straight running, and to improve the steering stability by increasing the increase in the lateral spring coefficient during cornering, for cords with a small angle to the circumferential direction, which are provided in at least one part from a bead portion to a sidewall portion, the cord rigidity during small deformation during straight running needs to be low, and the cord rigidity during large deformation during cornering needs to be high. As a result of the inventors' research and development, they found that such cord characteristics can be achieved by using non-linear elastic modulus cords for cords provided in at least one part from a bead portion to a sidewall portion.
Deformation states of a tire of the present embodiment, in which the non-linear elastic modulus cords illustrated in
Next, during cornering, although the bead portion is subjected to bending deformation and the sidewall portion is subjected to bulging deformation, as described using
The changes in the deformation state of the tire during straight running and during cornering allow the pneumatic tire of the present embodiment to achieve both ride comfort and steering stability at a high level.
As described above, in the pneumatic tire of the present embodiment, dimensions of a bead core are specified and a bead filler is small. This reduces both the vertical spring coefficient and the lateral spring coefficient of the tire. This improves the ride comfort during straight running, but may reduce the steering stability during cornering. In this regard, cords provided in at least one part from a bead portion to a sidewall portion in the tire circumferential direction can compensate for reduced size of the bead filler and improve the vertical spring coefficient and the lateral spring coefficient of the tire.
However, when the cord is not a non-linear elastic modulus cord, the cord is used always with tensile stress applied to reinforce a bead filler, and although the cord has sufficient steering stability during cornering, the vertical spring coefficient may be too high, worsening the ride comfort during straight running, or the ride comfort during straight running may be favorable, but sufficient steering stability during cornering may deteriorate. In contrast, since the cord 9 is a non-linear elastic modulus cord, the pneumatic tire of the present embodiment has a low elastic modulus property in a low-strain region, which allows the tire to have sufficient steering stability during cornering while lowering the vertical spring coefficient for favorable ride comfort during straight running. Therefore, while reducing the weight of a tire by reducing the size of a bead filler, excellent steering stability during cornering and favorable ride comfort during straight running can be obtained. By adjusting the properties of the non-linear elastic modulus of the cord, weight reduction of the tire, excellent steering stability during cornering, or favorable ride comfort during straight running can be adjusted.
Next, the non-linear elastic modulus cord of a pneumatic tire of the present embodiment will be described in more detail.
The elastic modulus of a non-linear elastic modulus cord is measured by cutting the cord out of the tire. In other words, the non-linear modulus cord is a cord that, when incorporated into an actual tire, exhibits a low elastic modulus or a high elastic modulus depending on the deformation during straight running or during cornering.
A specific method of measuring the elastic modulus is as described below. A test is conducted in the same way as the test for “Tensile Strength and Elongation” in accordance with JIS L1017, and the tensile strength and elongation are measured. From these measurement results, a curve is drawn in a graph with the tensile strain, which is the ratio of the initial length to the elongation length, and the stress on the vertical axis. In the curve of the graph with the stress on the Y-axis and the strain on the X-axis, the point where the perpendicular line passing through the intersection of the tangent line drawn on the curve when the strain is zero and the tangent line drawn on the curve at the breaking point intersects the curve is the inflection point.
This inflection point is preferably in the range of 1 to 8% tensile strain. The elastic modulus in the low-strain region is preferably in the range of 10 to 90% of the elastic modulus in the high-strain region.
It is more preferable for a cord to have a non-linearity such that the elastic modulus in the high-strain region is more than twice as large as the elastic modulus in the low-strain region. The ratio of the elastic modulus in the low-strain region to the elastic modulus in the high-strain region is represented by the ratio of the slope of the straight line connecting the strain zero to the inflection point to the slope of the straight line connecting the inflection point to the breaking point.
It is conceivable that, for the cords forming a small angle with respect to the circumferential direction, the non-linear elastic modulus cord provided in the pneumatic tire of the present embodiment is not used, and that, for example, a cord with a low rigidity is provided on the inner side in the tire radial direction, and a cord with a high rigidity is provided on the outer side in the tire radial direction. However, tires using a plurality of kinds of cords have durability issues, such as strain concentration in the rubber where the rigidity changes in the tire radial direction, or where different kinds of cords are switched, resulting in cracks during use. In contrast, in this pneumatic tire of the present embodiment, by using a cord with a non-linear elastic modulus property, the rigidity in the tire radial direction due to the non-linear modulus cord changes gradually. Therefore, strain concentration in the rubber can be avoided, and the durability can be improved.
A non-linear elastic modulus cord may be composed of two or more kinds of fibers of different materials, and the fibers may be composed of organic fibers or inorganic fibers.
In order to realize a non-linear elastic modulus cord, two or more kinds of materials with different elastic moduli, in one example, a cord with a low elastic modulus and a cord with a high elastic modulus, are used. Anon-linear modulus cord formed by twisting two cords of different moduli together can exhibit low elastic modulus cord characteristics at low strain and high elastic modulus cord characteristics at high strain. As a result, a non-linear elastic modulus property can be obtained. The non-linear elastic modulus properties can be adjusted by selecting the material.
Organic fibers or inorganic fibers used for tires can be used as the material for non-linear elastic modulus cords. Examples of the organic fibers include nylon, polyethylene terephthalate, polyethylene naphthalate, and aramid. Examples of the inorganic fibers include glass fiber, carbon fiber, and steel. From these materials, materials with different elastic moduli are combined. For example, nylon, which has the lowest elastic modulus among these materials, can be selected as the material with a low elastic modulus, any of the above-described materials other than nylon can be selected as the material with a high elastic modulus, and these materials can be combined. Polyethylene terephthalate can be selected as the material with a low elastic modulus, any of polyethylene naphthalate, aramid, glass fiber, carbon fiber, or steel can be selected as the material with a high elastic modulus, and the selected materials can be combined. In addition, polyethylene naphthalate can be selected as the low elastic modulus material, any of aramid, glass fiber, carbon fiber, or steel can be selected as the material with a high elastic modulus, and the selected materials can be combined.
By using aramid as at least one of the materials for the non-linear elastic modulus cord, external damage that may occur when a foreign object hits the cord during running can be controlled by taking advantage of a favorable cut resistance that aramid has. By using polyethylene terephthalate as at least one of the materials for the non-linear modulus cord, the elastic modulus can be increased at a low cost.
Materials applied to a non-linear elastic modulus cord and materials applied to a carcass may be different. When the materials for a non-linear elastic modulus cord is the same as the materials for a main body portion ply, strain concentration occurs in the rubber sandwiched in between at the intersection of the main body portion ply and the non-linear elastic modulus cord. In contrast, by using cords with different moduli, a low elastic modulus cord is pushed by a high elastic modulus cord, and the strain can be distributed between the cords.
The angle of the non-linear elastic modulus cord with respect to the tire circumferential direction is in the range of 0 to 10°. When the absolute value of the angle with respect to the tire circumferential direction exceeds 10°, the vertical spring coefficient during straight running becomes high, and the ride comfort deteriorates.
Arrangement of the non-linear elastic modulus cord is not particularly limited, and the cord can be arranged in at least one part from the bead portion to the sidewall portion, where deformation can occur. By arranging a non-linear elastic modulus cord with an appropriate elastic modulus in an appropriate position according to the deformation state of the tire during straight running and cornering, both ride comfort and steering stability can be achieved at a high level.
When arranged at least in a region including a bead portion, the non-linear elastic modulus cord 9 can be arranged between the main body portion ply of the carcass and the bead filler as illustrated in
By arranging the non-linear elastic modulus cord between the main body ply of the carcass and the bead filler as illustrated in
By arranging the non-linear elastic modulus cord between the bead filler and the folding-over portion ply of the carcass, as illustrated in
By arranging the non-linear elastic modulus cord outside the folding-over portion ply of the carcass in the tire radial direction as illustrated in
A non-linear elastic modulus cord that has an appropriate elastic modulus in the tire may be prepared. The non-linear elastic modulus properties of the non-linear elastic modulus cord may be utilized to control the elastic modulus of the product by deformation during the tire manufacturing process. When tensile deformation is applied to the non-linear elastic modulus cord in the direction of the cord during the tire manufacturing process, the cord can be easily deformed by utilizing properties of low strain and low elasticity, and controlled and appropriate non-linear elastic modulus properties can be obtained inside the product tire.
The non-linear elastic modulus cord may have different non-linear elastic modulus properties within the tire, depending on where the cord is arranged in the tire. By arranging a non-linear elastic modulus cord with appropriate non-linear elastic modulus properties according to the deformation that varies depending on position in the tire, the ride comfort and the steering stability can be improved in a high balance.
A plurality of kinds of non-linear elastic modulus cords with different non-linear elastic modulus properties depending on position in the tire may be prepared before the tire molding process, however, by preparing one or more kinds of non-linear elastic modulus cords and applying different tensions to the non-linear elastic modulus cords depending on the position in the tire in the tire molding process during tire manufacturing, the elastic modulus of the non-linear elastic modulus cords can be controlled depending on the position in the product tire to obtain more kinds of non-linear elastic modulus cords in the tire than the prepared non-linear elastic modulus cords. By changing the tension of the non-linear elastic modulus cord according to the position in the tire during the manufacturing process, the elastic modulus of the cord can be changed, and therefore the elastic modulus can be changed according to the position in the tire while using the same material. Therefore, the number of kinds of materials for the non-linear elastic modulus cord to be prepared can be reduced, and the cord can be produced efficiently.
By controlling the tension applied during tire manufacturing in this way, tires with a variety of properties can be obtained. For example, in the tire molding process, the non-linear elastic modulus cord in the sidewall portion is greatly stretched in the circumferential direction because a member wound on a drum is expanded into a raw tire. Therefore, in the sidewall portion, the high-strain region of the non-linear elastic modulus cord is used, resulting in a higher rigidity than the non-linear elastic modulus cord in the bead portion. By so doing, the rigidity of the tire during cornering can be increased more effectively.
For example, the elastic modulus can be changed by the tension during manufacturing, and the non-linear elastic modulus cord in the bead portion can have a higher elastic modulus than the sidewall portion. As a result, the rigidity of the tire during cornering can be increased slightly.
For example, by expansion and tension in the tire molding process, the non-linear elastic modulus cord extending from the bead portion to the sidewall portion can also have a high elastic modulus in the center portion in the tire radial direction. As a result, the rigidity of the tire during cornering can be moderately increased.
Data for testing using the following test method is shown in Table 1.
Passenger car tires with a tire size of 205/60R16 92V are manufactured by arranging a variety of cords of Conventional Example, Comparative Examples, and Examples shown below in a bead portion. In this case, three different types of bead core shapes illustrated in
Conventional Example: Bead core of
Comparative Example 1: Bead core of
Comparative Example 2: Bead core of
Comparative Example 3: Bead core of
Example 1: Bead core of
Example 2: Bead core of
Example 3: Bead core of
Example 4: Bead core of
Example 5: Bead core of
As shown in Table 1, Examples 1 to 5 provide favorable ride comfort with no increase in the vertical spring coefficient compared to Conventional Example, and provide favorable steering stability with an increase in the lateral spring coefficient compared to Conventional Example. In contrast, Comparative Examples 1 and 3 provide deteriorated ride comfort with an increase in the vertical spring coefficient compared to Conventional Example.
The pneumatic tire of the present invention has been described above by way of embodiments and Examples, but the pneumatic tire of the present invention can be modified in many ways without departing from the gist of the present invention.
1 Pneumatic tire, 2 Bead portion, 3 Sidewall portion, 4 Tread portion, 5 Bead core, 6 Bead filler, 7 Carcass, 8 Belt, 9 Cord
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-233923 | Dec 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/049039 | 12/13/2019 | WO | 00 |
