Patent Application
20180126801
The present invention relates to a heavy load pneumatic radial tire especially suitable as a construction vehicle tire.
A heavy load pneumatic radial tire used for a construction vehicle or the like needs to have sufficient tightening margins secured to the bead base portion of the tire with respect to the bead sheet portion of the rim in order to prevent slipping between the rim and the tire at the time of rolling of the tire and maintain airtightness between the rim and the tire.
It is especially important for a tubeless tire, unlike a tube tire, to maintain airtightness in this manner in order to hold the air pressure inside the tire at the initial pressure set by air filling as long as possible in expectation of the effect of air sealing between the rim and the bead portion.
Patent Literature 1: JP 2000-233613 A
Patent Literature 2: JP 2001-206027 A
When a heavy load pneumatic radial tire provided with sufficient tightening margins is mounted to a rim, the diameter of a bead base portion increases, that is, a rubber chafer corresponding to the bead base portion undergoes apparent compression (because rubber is incompressible). At this time, much of the rubber forming the rubber chafer undergoes flow deformation in the directions of a bead heel portion and a bead toe portion.
At the bead heel portion, in particular, the flow deformation of the rubber is restricted by a rim flange, and hence the corresponding rubber portion undergoes flow deformation toward the outside in the tire radial direction. Because a reinforcing cord layer (for example, a wire chafer) adjacent to the bead core side of the rubber chafer restrains the flow deformation of the rubber chafer, shear strain occurs in the rubber chafer.
With an increase in load at the time of rolling of the tire, the movement of a carcass in the radial direction increases, and the flow deformation of the rubber chafer increases, resulting in an increase in shear strain. This tends to cause a separation failure at the boundary surface between the rubber chafer and the wire chafer in an area corresponding to the bead heel portion at which the shear strain in the rubber chafer becomes the maximum.
The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a heavy load pneumatic radial tire that can prevent slipping by securing sufficient tightening margins to the bead portion and prevent the occurrence of separation between the rubber chafer and the wire chafer at a bead heel portion.
To solve the problems described above, a heavy load pneumatic radial tire according to an aspect of the present invention includes a carcass folded back at a bead core, and a wire chafer arranged on an outer circumference of the carcass and folded back around the bead core. A reinforcing rubber layer having a lower elastic modulus than at least one of coating rubber forming the carcass and coating rubber forming the wire chafer is arranged between the carcass and the wire chafer. An area where the reinforcing rubber layer is arranged is an area corresponding to at least part of a range of rotational angles of −45° to 90° around a bead core center to outward in a tire widthwise direction with reference to a straight line extending inward in a tire radial direction from the bead core center, intersecting orthogonally to the tire widthwise direction, and intersecting with the wire chafer.
The aspect of the present invention provides a heavy load pneumatic radial tire that can prevent slipping by securing sufficient tightening margins to the bead portion and prevent the occurrence of separation between the rubber chafer and the wire chafer at a bead heel portion.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same or similar parts are denoted by the same or similar reference numerals, and the detailed description thereof is appropriately omitted.
In addition, the following embodiments are examples for embodying the technical idea of the present invention, and the embodiments of the present invention do not specify the material, shape, structure, arrangement, etc. of constituent parts to the followings. The embodiments of the present invention can be implemented with various modifications without departing from the gist. Further, in the embodiments, the numerical values when the conditions are not specified are numerical values in the no-load state in which the rim is assembled to the regular rim and the internal pressure is 50 kPa.
The first embodiment will be described first.
A heavy load pneumatic radial tire 10 according to the first embodiment includes a carcass (carcass ply) 14 folded back at a bead core 12. In the first embodiment, the height of a folded portion 14r of the carcass 14 reaches 40% to 60% of the radial direction cross-section height of the tire.
In addition, the heavy load pneumatic radial tire 10 includes at least two belt layers (not shown) arranged outside the carcass 14 in the tire radial direction and a tread rubber layer (not shown) arranged outside the belt layers in the tire radial direction.
A bead portion 16 includes a bead toe portion 18, a bead heel portion 20, and a wire chafer 22 formed from a steel cord reinforcing layer arranged on the outer circumference of the carcass 14. The wire chafer 22 is folded back around the bead core 12. The type of rubber used as coating rubber forming the wire chafer 22 is the same as that used for a rubber chafer 26 to describe later.
In addition, the heavy load pneumatic radial tire 10 includes a reinforcing rubber layer 24 between the carcass 14 and the wire chafer 22. The reinforcing rubber layer 24 has an elastic modulus lower than that of at least one of coating rubber forming the carcass 14 and coating rubber forming the wire chafer 22.
In the first embodiment, the type of rubber used for the reinforcing rubber layer 24 is the same as that of an inner liner, and has an elastic modulus of 8 MPa to 14 MPa at 300% elongation. The “elastic modulus at 300% elongation” of the inner liner and the reinforcing rubber layer 24 is a measurement complying with DIN standards, which is a tensile elastic modulus at 300% elongation obtained by conducting a tensile test at a tension rate of 100 (mm/min) with respect to a test specimen obtained by slicing a rubber material with a thickness of about 0.5 mm and punching the sliced piece by using a blade die complying with DIN standards.
A thickness t of the reinforcing rubber layer 24 is set to at least 0.5 mm or more except for end portions. Note that the range of each of end portions 24e and 24i of the reinforcing rubber layer 24 corresponds to the range of 10 mm from an end face of the reinforcing rubber layer 24.
An area where the reinforcing rubber layer 24 is arranged is an entire area corresponding to a range of rotational angles θ of −120° to 120° around a center 12c from a wire chafer underneath portion 22b located immediately below a center 12c of the bead core 12 to an tire outside E (toward a rim flange RF). In other words, the area where the reinforcing rubber layer 24 is arranged is the entire area corresponding to the range of the rotational angles θ of −120° to 120° around the center 12c of the bead core 12 outward in the tire widthwise direction with reference to a straight line that extends from the center 12c of the bead core 12, intersects the tire widthwise direction at a right angle, extends toward the inner side in the tire radial direction, and intersects the wire chafer 22. This range is set in accordance with the dimensions of the bead core 12, the dimensions of the tire, and the like. Note that the range can be an area forming at least part of the range of −45° to 90°.
In this case, a straight line L connecting the center 12c of the bead core 12 and the wire chafer underneath portion 22b is orthogonal to a tire axial direction C (a straight line passing through the tire center). In addition, 0° indicates the position of the wire chafer underneath portion 22b. Accordingly, the rotational angle θ around the center 12c from the wire chafer underneath portion 22b to a tire inside I is indicated with a minus sign.
The first embodiment can achieve a reduction in shear strain near the boundary surface between the rubber chafer 26 of the bead heel portion 20 and the wire chafer 22, which poses a problem in the conventional structure. This can effectively prevent the occurrence of a separation failure (tire failure) between the rubber chafer 26 and the wire chafer 22. Setting the range of the rotational angles θ to a range smaller than that described above tends to make it difficult to effectively prevent the occurrence of a tire failure.
The area where the reinforcing rubber layer 24 is arranged is preferably an area that is at least part of the range of the rotational angles θ of −150° to 150°, and preferably includes the entire area ranging from −120° to 120°. This can further effectively prevent the occurrence of a tire failure. Note that when the above area is set to an area that is at least part of the above range of the rotational angles θ of −45° to 90°, the area preferably includes an entire area ranging from 45° to 80° in consideration of further effectively preventing the occurrence of a tire failure.
An outside reinforcing layer 28 formed from a rubber material (that is, the same type of rubber as that used for the inner liner) with an elastic modulus at 300% elongation ranging from 8 MPa to 14 MPa is arranged on the outer circumference of the wire chafer 22.
The thickness of the outside reinforcing layer 28 is set to at least 1.0 mm or more except for end portions. In addition, the outside reinforcing layer 28 is separated from a bead base 30 by at least 1 mm or more. Note that each of the ranges of end portions 28e and 28i of the outside reinforcing layer 28 is located within the range of 10 mm from the end face.
The rubber chafer 26 having an elastic modulus at 300% elongation ranging from 9 MPa to 15 MPa is arranged between the wire chafer 22 and the bead base 30. In this case, “elastic modulus at 300% elongation” of the rubber chafer 26 is a tensile elastic modulus (M300) at 300% elongation at room temperature (25°), which is measured in conformity to JIS K6301.
The operation and effect of the first embodiment will be described below. As shown in
Assume that in this case, a “normal rim” indicates a standard rim defined by the following standards in accordance with the size of a tire. Assume also that a “normal internal pressure” indicates an air pressure corresponding to the maximum load carrying capacity of a single tire with an applicable size written in the following standards. Furthermore, assume that a “normal load” indicates the maximum load (maximum load carrying capacity) of a single tire with an applicable size in the following standards. The standards in this case are industrial standards effective in areas where tires are produced or used, and include, for example, “JATMA YEAR BOOK” published by THE JAPAN AUTOMOBILE TIRE MANUFACTURERS ASSOCIATION in Japan, “YEAR BOOK” published by THE TIRE AND RIM ASSOCIATION INC. in the United States, and “STANDARD MANUAL” published by The European Tyre and Rim Technical Organisation in Europe. Note that in this specification, the following description and the like are made in consideration of these standards.
In addition, the height of the folded portion 14r of the carcass 14 reaches 40% to 60% of the radial direction cross-section height of the tire. This can further effectively prevent the removal of the carcass 14.
The outside reinforcing layer 28 formed from a rubber material (that is, the same type of rubber as that used for the inner liner) having an elastic modulus at 300% elongation in the range of 8 MPa to 14 MPa is arranged on the outer circumference of the wire chafer 22. This structure obtains a buffering effect from the outside reinforcing layer 28 and can further effectively prevent the occurrence of a separation failure between the rubber chafer 26 and the wire chafer 22.
The thickness of the outside reinforcing layer 28 is set to at least 1.0 mm or more except for the end portions 28e and 28i. This makes it possible to easily obtain a sufficient effect from the outside reinforcing layer 28.
In addition, the outside reinforcing layer 28 is separated from the bead base 30 by at least 1 mm or more. This easily accentuates the effect obtained by arranging the outside reinforcing layer 28.
Note that organic fiber cords may be arranged in the outside reinforcing layer 28. This can effectively increase the strength of the outside reinforcing layer 28 without increasing the thickness of the outside reinforcing layer 28. In addition, the same effect can be obtained by arranging organic fiber cords between the wire chafer and the outside reinforcing layer 28.
In addition, in order to sufficiently reduce the weight of the heavy load pneumatic radial tire 10, the compression ratio of the bead portion 16 obtained when being mounted to the rim is preferably set to 0.3 or more. In this case, the compression ratio of the bead portion 16, as shown in
The present inventors conducted an experiment for performance evaluation by using an example tire (to be referred to as Example 1 hereinafter) as an example of the heavy load pneumatic radial tire 10 according to the first embodiment and a prior art tire (to be referred to as Prior Art 1 hereinafter). According to Example 1, a sheet-like member (corresponding to about one sheet) having a width t of 100 mm and a thickness of 1.65 mm was arranged as a reinforcing rubber layer in an area ranging from a wire chafer end 22e on a rim flange RF to a position immediately below the center 12c of the bead core 12. Prior Art 1 does not have such a reinforcing rubber layer.
In this experimental example, Example 1 and Prior Art 1 each were mounted to a normal rim, and shear strain near the boundary surface between the rubber chafer 26 of the bead heel portion 20 and the wire chafer 22 was measured at the time of rolling, the measured value was converted into an evaluation index, thereby performing performance evaluation.
The following are experimental conditions:
tire size: 59/80R63 VRF
rim size: 44.00/5.0
internal pressure: 600 kPa
load: 100.0 ton
As shown in
The prevent inventors also conducted performance evaluation by performing analytical calculations with respect to an embodiment tire (to be referred to as Example 2 hereinafter) as an example of the heavy load pneumatic radial tire 10 according to the first embodiment and a prior art tire (to be referred to as Prior Art 2 hereinafter).
According to Example 2, a reinforcing rubber layer of the same rubber type as that of the inner liner was arranged as the reinforcing rubber layer 24 between the carcass 14 and the wire chafer 22. A sheet-like member (corresponding to about one sheet) having a thickness t of 1.65 mm was arranged as this reinforcing rubber layer in an area ranging from the wire chafer end 22e on the rim flange RF to a position immediately below the center 12c of the bead core 12. Prior Art 2 does not have such a reinforcing rubber layer.
As is obvious from
In this case, when the periphery length is 10 mm, the rotational angle θ is 5°; when the periphery length is 30 mm, the rotational angle θ is 30°; when the periphery length is 50 mm, the rotational angle θ is 60°; when the periphery length is 70 mm, the rotational angle θ is 80°; and when the periphery length is 90 mm, the rotational angle θ is 100°.
Accordingly, all the areas in the range of periphery lengths of 10 mm to 90 mm correspond to all the areas in the range of the rotational angles θ of 5° to 100°. In addition, even if the tire size differs from that (59/80R63 VRF) in this analytical calculation example, arranging a reinforcing rubber layer having a corresponding size makes it possible to obtain calculation results similar to those in the analytical calculation example within the range of the rotational angles θ of 5° to 100°.
The second embodiment will be described next.
A heavy load pneumatic radial tire 40 according to the second embodiment is structured to increase tightening margins at a bead heel portion 50 upon mounting to a normal rim R as compared with the heavy load pneumatic radial tire 10 according to the first embodiment. This structure will be described in detail with reference to
A point A is a point of intersection between a perpendicular line LA drawn orthogonally to the rim base RB from the center 12c of the bead core 12 when the tire 40 is assembled to the rim R and the rim base RB. In addition, a point B is a point of intersection between the perpendicular line LA and a bead base 48 when the tire 40 is not assembled to the rim R. Furthermore, a point H is a point of intersection between a rim flange RF and the rim base RB. A point D is a point at which a line segment AH is divided at a ratio of 7:3. A point J is an arbitrary point on a line segment AD. A point F is a point of intersection between a straight line LJ passing through the point J extending orthogonal to the rim base RB and the bead base 48.
Letting X be the length of the line segment AB and Y be the length of the line segment JF, Y is 90% or more of X in the entire range of the line segment AD, that is, Y and X satisfy the relation given by
Y≥0.9X
Note that X is, for example, 8.68 mm, and Y is, for example, in the range of 8.35 mm to 8.68 mm.
As described above, the second embodiment adopts the tire structure that increases tightening margins near the bead heel portion 50 as compared with the prior art instead of monotonously increasing tightening margins to the bead base 48 with respect to the rim base RB. This eventually effectively increases the fitting force between the bead base 48 and the rim base RB in the second embodiment. That is, the second embodiment provides the effects of preventing a rim-slipping phenomenon and preventing the occurrence of air leak in addition to the effects obtained by the first embodiment.
The present inventors conducted an experiment for performance evaluation by using an example tire (to be referred to as Example 3 hereinafter) as an example of the heavy load pneumatic radial tire 40 according to the second embodiment and a prior art tire (to be referred to as Prior Art 3 hereinafter). In Example 3, the lengths X and Y in
In this experimental example, Example 3 and Prior Art 3 each were mounted to a normal rim, and the tightening margins to the bead base 48 with respect to the rim base RB were measured at the position of the point D and converted into evaluation indices, thereby conducting performance evaluation. Experimental conditions (a tire size, rim size, internal pressure, and load) were the same as those in Experimental Example 1.
With regard to the evaluation indices in
It should be noted that the present application claims priority to Japanese Patent Application No. 2015-102517, filed on May 20, 2015, the entire contents of which are incorporated by reference herein.
The aspect of the present invention provides a heavy load pneumatic radial tire that can prevent slipping by securing sufficient tightening margins to the bead portion and prevent the occurrence of separation between the rubber chafer and the wire chafer at a bead heel portion.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-102517 | May 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/063388 | 4/28/2016 | WO | 00 |
