JP5986502B2 - Evaluation method of carcass durability at bead part of heavy duty tire - Google Patents

Description

  The present invention relates to a carcass durability evaluation method in a bead portion of a heavy load tire that can reproduce damage caused by rubbing of a carcass cord with a bead core in a short test time and can accurately evaluate carcass durability in a short test time.

  As shown in FIG. 6, a bead core “b” having a polygonal cross section in which steel wires are wound in multiple rows and stages, and a normal hexagonal cross section is disposed in the bead portion “a” of the heavy duty tire. Further, both ends of the carcass ply c forming the tire skeleton are locked by being folded around the bead core b.

  However, since the heavy duty tire is used under severe conditions of high internal pressure and high load, a large tension force f acts on the carcass cord of the carcass ply c. As a result, in the carcass cord, so-called fretting occurs that strongly rubs with the corner portion b1 located at the innermost point P in the tire axial direction of the bead core b. As the wear due to fretting progresses, the strength of the carcass cord is lowered, and eventually the cord breaks, resulting in a tire burst.

  In order to suppress the fretting, various research and development have been conducted. For example, in Patent Document 1, a rubber layer containing short fibers is formed around the bead core to prevent direct contact between the carcass cord and the bead core. It has been proposed. Patent Document 2 proposes that two bead reinforcing layers are provided to suppress bead deformation and that a highly elastic rubber layer is interposed between the carcass cord and the bead core. Patent Document 3 proposes that a bead core is made elastic by forming a rubber core inside the bead core.

  The researched and developed tire requires an evaluation test to evaluate its effect. However, there is no effective test method for reproducing fretting in the bead portion in a short test time and accurately evaluating the carcass durability in a short test time, and its appearance has been strongly demanded.

JP 2000-085322 A JP 2012-106531 A Japanese Patent Laying-Open No. 2005-041392

  Therefore, the present invention provides a carcass durability evaluation method in a bead portion of a heavy duty tire that can reproduce damage caused by rubbing of a carcass cord with a bead core in a short test time and can accurately evaluate carcass durability in a short test time. The challenge is to do.

The invention according to claim 1 of the present invention is folded from the inner side to the outer side in the tire axial direction around the bead core on both sides of the toroidal ply main body part extending from the tread part through the sidewall part to the bead core of the bead part. A carcass durability evaluation method in the bead portion of the heavy load tire comprising a carcass made of a carcass ply provided with a series of ply folded portions that are locked in place,
A running process in which a test tire assembled with a rim is pressed against a rotating drum and runs on the drum;
Including an evaluation process for evaluating carcass durability in a bead portion of a tire that has traveled,
The running step, 160 to 260% of the internal pressure P is normal internal pressure _{P 0} of the test tires, the load F is from 350 to 450% of the normal load _{F 0,} and the traveling velocity V is 15~40km / h,
Moreover, in the tire meridional section, when the angle with respect to the tire axial direction line of the reference line X passing through the innermost point in the tire axial direction of the bead core and the maximum width point in the tire axial direction of the carcass ply is θ,
A state in which the test tire is pressed against the drum under the condition of the angle θ value θ ₀ in the no-load normal internal pressure state in which the test tire is filled with the normal internal pressure and no load is applied, and the internal pressure P and the load F in the running process The test tire is run in a bent state in which the difference (θ ₀ −θ ₁ ) between the angle θ and the value θ ₁ is in the range of 5 to 15 °.

  According to a second aspect of the present invention, the evaluation step disassembles a test tire after traveling an evaluation distance in a range of 600 to 1200 km in the traveling step, and a carcass cord flare at a position of the innermost point in the tire axial direction of the bead core. It is characterized by evaluating the amount of ting.

  Here, the “regular internal pressure” is an internal pressure determined for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is determined by JATMA, and the table “TIRE LOAD LIMITS” is measured by TRA. The maximum value described in "AT VARIOUS COLD INFLATION PRESSURES". If ETRTO, it means "INFLATION PRESSURE". The “regular load” is a load determined by the standard for each tire corresponding to the regular internal pressure. If it is JATMA, it is the maximum load capacity, and if it is TRA, “TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES” If it is the maximum value described in ETRTO, it means “LOAD CAPACITY”.

  In the present invention, the traveling conditions in the traveling process are defined as described above. Therefore, as will be described in the section “DETAILED DESCRIPTION OF THE INVENTION” below, it is possible to reproduce with high accuracy the damage caused by rubbing the carcass cord with the bead core in a short test time. As a result, carcass durability can be accurately evaluated in a short test time, which can greatly contribute to tire research and development.

It is a conceptual diagram which shows the implementation condition of the evaluation method of the carcass durability in the bead part of this invention. It is sectional drawing which shows an example of the tire for heavy loads in which the evaluation method of the carcass durability in the said bead part is implemented. (A) is a schematic cross-sectional view for explaining the angle difference (θ ₀ −θ ₁ ) in the tire with a tube, and (B) is a schematic cross-sectional view for explaining the angle difference (θ ₀ −θ ₁ ) in the tubeless tire. (A) is a graph showing the relationship between the internal pressure ratio P / P ₀ and the fretting amount and its variation σ, and (B) is a graph showing the relationship between the load ratio F / F ₀ and the fretting amount and its variation σ. is there. (A) is a graph showing the relationship between the running speed V and the fretting amount and its variation σ, and (B) is a graph showing the relationship between the angle difference (θ ₀ −θ ₁ ) and the fretting amount and its variation σ. It is. It is sectional drawing which shows the bead part of the tire for heavy loads.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a conceptual diagram showing an implementation status of a carcass durability evaluation method (hereinafter referred to as “carcass durability evaluation method”) in a bead portion according to the present invention. The test tire 1 is configured to include a travel process in which the test tire 1 is pressed against the rotating drum 10 and travels on the drum 10 and an evaluation process for evaluating the carcass durability in the bead portion 4 of the traveled test tire 1.

  As the drum 10, a drum having a known structure for a tire running test can be appropriately employed. As the test tire 1, as shown in FIG. 2, heavy load tires T having various structures including a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4 are applied. The In this example, the heavy load tire T is a radial tire with a tube.

  The carcass 6 is formed of one or more, in this example, one carcass ply 6A in which metal carcass cords are arranged at an angle of, for example, 75 ° to 90 ° with respect to the tire circumferential direction. The carcass ply 6A includes a toroid-like ply main body 6a straddling between the bead cores 5 and 5, and a ply turn-up portion that is connected to both sides of the bead core 5 and is folded and locked from the inner side to the outer side in the tire axial direction around the bead core 5. 6b. Further, a bead apex rubber 8 for bead reinforcement extending radially outward from the bead core 5 is disposed between the ply main body portion 6a and the ply turn-up portion 6b.

  The bead core 5 is formed as a ring body having a polygonal cross section in which steel wires are wound in multiple rows and stages. The bead core 5 of this example has a hexagonal cross section, and one side thereof is substantially parallel to the rim sheet Rs, so that the fitting force with the rim R is uniformly maintained. In such a bead core 5 having a hexagonal cross section, a hexagonal corner 5a is arranged at the position of the innermost point P in the tire axial direction.

  A belt layer 7 for reinforcing the tread is disposed outside the carcass 6 in the radial direction and inside the tread portion 2. The belt layer 7 is formed of two or more belt plies 7A to 7D in this example in which belt cords are arranged at an angle of, for example, 10 to 70 ° with respect to the tire circumferential direction.

Next, in the running process in the carcass durability evaluation method,
(A) internal pressure P of the test tire 1, 160 to 260% of the normal inner pressure _{P 0,}
(A) The load F is 350 to 450% of the normal load F ₀ ,
(C) The traveling speed V is 15 to 40 km / h,
Moreover, the test tire 1 is run on the drum 10 in the following bent state Y.

As shown in FIG. 3A, the bending state Y is a reference that passes through the innermost point P in the tire axial direction of the bead core 5 and the maximum width point M in the tire axial direction of the carcass ply 6A in the tire meridional section. When the line is X, it is a tire deflection state defined based on the angle θ of the reference line X with respect to the tire axial direction line. Note the tire axial maximum width point M is in the normal inner pressure state Y ₀ unloaded without filling the normal inner pressure P ₀ in the test tire 1 and a load, position the carcass ply 6A overhangs most axially outward Identified as

Specifically, the value θ _{0 of the} angle θ in the no-load normal internal pressure state Y _{0 and} the angle θ in a state where the test tire 1 is pressed against the drum 10 under the conditions of the internal pressure P and the load F in the traveling process. This is a bending state Y in which the difference (θ ₀ −θ ₁ ) from the value θ ₁ is in the range of 5 to 15 °. As shown in FIG. 3B, the angle θ is similarly defined in the case of a tubeless tire, and the difference (θ ₀ −θ ₁ ) is restricted to a range of 5 to 15 °.

In other words, in the traveling process,
- from 160 to 260% of the range of the internal pressure P of the regular internal pressure _{P 0,}
Load F in the range of 350 to 450 percent of the normal _{load-F 0,}
A velocity in the range of 15 to 40 km / h, and a bending state Y in which the angle difference (θ ₀ −θ ₁ ) of the reference line X is in the range of 5 to 15 °,
The test tire 1 is run on the drum 10 under the following conditions.

The angle difference (θ ₀ −θ ₁ ) can be easily set within the range by adjusting the balance between the internal pressure P and the load F within the range.

  By setting such conditions, damage to the carcass cord caused by rubbing between the carcass cord and the bead core 5 at the position of the innermost point P (corner portion 5a) can be reproduced with a short test time and with high accuracy. It becomes. As a result, the carcass durability can be accurately evaluated in a short test time.

Incidentally, as shown in FIG. 4 (A), the internal pressure P is, if less than 160% of the normal inner pressure P _0, since the tension acting on the carcass cord is reduced, the reduction of evaluation time takes a long time to progression of wear It cannot be achieved sufficiently. On the other hand, if it exceeds 260%, wear is promoted, but the progress variation becomes large, and the evaluation accuracy is lowered. Further, since the variation becomes large, there is a possibility that the tire may burst during the traveling process. From this point of view, the lower limit of the internal pressure P is preferably 180% or more of the normal inner pressure _{P 0,} the upper limit is preferably 240% or less. It should be noted that it is preferable to provide a pressure regulating valve or the like in order to prevent the internal pressure P from rising from the initial set position due to the temperature rise of the running tire, that is, to keep the internal pressure P constant.

As shown in FIG. 4B, when the load F is less than 350% of the normal load F ₀ , the tension acting on the carcass cord is reduced and the contact pressure of the carcass cord with the bead core 5 is also reduced. . For this reason, the progress of wear takes time, and the evaluation time cannot be sufficiently shortened. On the other hand, if it exceeds 450%, wear is promoted, but the progress variation becomes large, and the evaluation accuracy is lowered. Further, since the variation becomes large, there is a possibility that the tire may burst during the traveling process. From this point of view, the lower limit of the load F 330% or more preferably of normal load _{F 0,} the upper limit 420% or less is preferable.

  As shown in FIG. 5 (A), when the traveling speed V is less than 15 km / h, the repetition frequency of bead deformation decreases, so that wear progress takes time and the evaluation time cannot be sufficiently shortened. On the other hand, if it exceeds 40 km / h, wear is promoted, but the progress variation becomes large, resulting in a decrease in evaluation accuracy. Further, since the variation becomes large, there is a possibility that the tire may burst during the traveling process. Further, the internal temperature of the tread portion 2 rises, and there is a risk that the tread portion 2 is damaged earlier and the running process cannot be continued. From such a viewpoint, the lower limit of the traveling speed V is preferably 18 km / h or more, and the upper limit is preferably 30 km / h or less.

Also, as shown in FIG. 5B, when the angle difference (θ ₀ −θ ₁ ) is less than 5 °, the tire deflection is reduced, and the contact pressure of the carcass cord with the bead core 5 is reduced. For this reason, the progress of wear takes time, and the evaluation time cannot be sufficiently shortened. On the other hand, if the angle exceeds 15 °, wear is promoted, but the variation in progress increases, leading to a decrease in evaluation accuracy. Further, since the variation becomes large, there is a possibility that the tire may burst during the traveling process. Further, the bend damage, which is rubber peeling starting from the folded end of the carcass ply 6A (the outer end in the radial direction of the ply folded portion 6b), may occur first and the running process may not be continued due to excessive bending. Invite. From such a viewpoint, the lower limit of the angle difference (θ ₀ −θ ₁ ) is preferably 7 ° or more, and the upper limit is preferably 12 ° or less.

FIG. 4A shows the internal pressure ratio P / measured in Table 1 of the following test results, measured at a constant load ratio (F / F ₀ = 350%) and a constant traveling speed (V = 20 km / h). and P _0, which is a graph showing the fretting amount and relationship of the variation sigma. FIG. 4B shows the load ratio F / F measured in Table 1 of the following test results, measured at a constant internal pressure ratio (P / P ₀ = 210%) and a constant traveling speed (V = 20 km / h). It is a graph which shows the relationship between ₀ , fretting amount, and its variation (sigma). FIG. 5A shows the following test results in Table 1, in which the internal pressure ratio is constant (P / P ₀ = 210%), the load ratio is constant (F / F ₀ = 370%), and the angle difference (θ ₀ −θ ₁ ) A graph showing the relationship between the running speed V, the fretting amount, and its variation σ, measured at a constant ((θ ₀ −θ ₁ ) = 9.2 °). FIG. 5B shows the angular difference (θ ₀ ) measured in Table 1 of the test results below, measured at a constant internal pressure ratio (P / P ₀ = 210%) and a constant traveling speed (V = 20 km / h). It is a graph which shows the relationship between-(theta) ₁ ), the fretting amount, and its variation (sigma).

  Next, in the evaluation step, in this example, the test tire 1 after traveling the evaluation distance predetermined in the traveling step is disassembled, and the carcass cord at the position of the innermost point P in the tire axial direction of the bead core 5 is disassembled. Evaluate the amount of fretting. The evaluation distance is preferably selected from a range of 600 to 1200 km. When the evaluation distance is less than 600 km, the fretting amount is reduced and it is difficult to obtain high evaluation accuracy. Further, even if the distance exceeds 1200 km, the variation in wear progress is small, but the test time is unnecessarily increased.

  As the fretting amount, a cross-sectional area, a wear depth, or a wear volume of a worn portion of the carcass cord can be employed. These can be obtained by observing the worn part of the carcass cord using a laser microscope, for example.

  In the evaluation process, on the premise of ensuring safety against bursts, it is also possible to measure and evaluate the travel distance or travel time from the start of travel in the travel process until the test tire 1 reaches the burst. it can.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  In order to confirm the effect of the present invention, a carcass durability evaluation test was performed according to the specifications shown in Table 1, using a commercially available heavy load tire (12.00R20-16PR) having a structure shown in FIG. 2 as a test tire. The test was performed on 10 tires under each condition, and the average value of the fretting amount and the variation σ of the fretting amount were compared.

Normal internal pressure P0 of the test tire 7.25KPa, normal load _{F 0} is 30.5KN. The fretting amount is determined by measuring the wear volume of the worn portion of the carcass cord at the position of the innermost point in the tire axial direction of the bead core using a laser microscope, and calculating the average value of the fretting amount in Comparative Example 1. Expressed with an index of 100. The higher the value, the faster the wear progress.

  As shown in Table 1, it can be confirmed that the test time can be shortened by increasing the progress speed of wear while suppressing the variation in fretting amount σ and improving the evaluation accuracy.

  In Comparative Examples 3 and 5, there were tires that burst during the running process. In Comparative Example 7, there was a tire in which the tread portion was peeled and damaged by heat generation during the running process. Further, in Comparative Example 9, there was a tire that caused peeling damage during the traveling process with the carcass folded end as a base point.

DESCRIPTION OF SYMBOLS 1 Test tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Ply main-body part 6b Ply folding | turning part 10 Drum M Tire axial direction maximum width point P Tire axial direction innermost point T Heavy duty tire

Claims (2)

A series of ply turn-around portions that are folded and locked from the inner side to the outer side in the tire axial direction around the bead core on both sides of the toroid-like ply main body portion extending from the tread portion through the sidewall portion to the bead core of the bead portion. A carcass durability evaluation method in the bead portion of a heavy duty tire having a carcass made of a carcass ply provided,
A running process in which a test tire assembled with a rim is pressed against a rotating drum and runs on the drum;
Including an evaluation process for evaluating carcass durability in a bead portion of a tire that has traveled,
The running step, 160 to 260% of the internal pressure P is normal internal pressure _{P 0} of the test tires, the load F is from 350 to 450% of the normal load _{F 0,} and the traveling velocity V is 15~40km / h,
Moreover, in the tire meridional section, when the angle with respect to the tire axial direction line of the reference line X passing through the innermost point in the tire axial direction of the bead core and the maximum width point in the tire axial direction of the carcass ply is θ,
A state in which the test tire is pressed against the drum under the condition of the angle θ value θ ₀ in the no-load normal internal pressure state in which the test tire is filled with the normal internal pressure and no load is applied, and the internal pressure P and the load F in the running process The carcass in the bead portion of the heavy-duty tire, wherein the test tire is run in a bent state in which the difference (θ ₀ −θ ₁ ) between the angle θ and the value θ ₁ is in a range of 5 to 15 °. Durability evaluation method. The evaluation step includes disassembling the test tire after traveling the evaluation distance in the range of 600 to 1200 km in the traveling step, and evaluating the fretting amount of the carcass cord at the position of the innermost point in the tire axial direction of the bead core. The method of evaluating carcass durability in a bead portion of a heavy duty tire according to claim 1.

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