JPH03208703A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve durability, manoeuvering stability and riding comfortableness by coating a belt cord composed of a specific single strand with topping rubber to form a belt ply, and specifying an elongation percentage of the belt cord before the rubber coating. CONSTITUTION:In a tire 1 a carcass 6 is provided between each bead of a bead part 4 and a belt layer 9 is arranged outside in the radial direction of the carcass 6 and inside a tread part 2. In this constitution, the belt layer 9 is formed of a plurality of belt plies 9A, 9B, which are formed by coating a belt cord 10 with topping rubber 13. The belt cord 10 is formed of a single strand 12 in which a plurality of metal filaments 11 are twined and spirally shaped with a pitch P of 10 - 20 mm. In the belt cord 10, an elongation percentage is determined 1.5 % or more in the case of 5 kg load per cord and 3.0 % or less in the case of 20 kg load per cord respectively, before the coating of the topping rubber 13.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a spirally shaped belt cord that has a large elongation rate under low loads and a small elongation rate under high loads. The present invention relates to pneumatic radial tires that have increased high-speed durability, improved handling stability, and ride comfort.

[Conventional technology]

Generally, in a radial tire, the belt layer that is placed around the crown of the toroidal carcass to reinforce the tread is made up of a large number of reinforcing elements such as cords or filaments, which are arranged in a cross-shape across the equator of the tire. It has multiple belt braces. This belt structure is
Circumferential rigidity to maintain the toroidal shape of the carcass,
Although it can exhibit shear rigidity that can withstand the shear force generated when the tire corners, the reinforcement cord is slanted with respect to the equatorial plane, resulting in poor adhesion and concentration of distortion at the interface with the rubber at the cut end. There is a problem of delamination between the layers, which poses a serious problem in terms of tire durability.

[Problem to be solved by the invention]

Further, since the belt cord used for such a belt layer is usually a straight line made by twisting a plurality of filaments, the elongation rate is low and the elastic modulus is high.

As a result, the tread rigidity increases, leading to a rough feeling when running, which greatly impairs ride comfort.In addition, when the belt is repeatedly deformed during contact/non-contact, a large amount of stress is concentrated at the end of the belt, and the end It is easy to cause so-called separation, which occurs when the rubber separates from the rubber.

As a means to solve this problem, we have developed a belt cord strip with reinforcing elements consisting of multiple cords or filaments arranged in a wavy or zigzag pattern, with the orientation of the reinforcing elements parallel to or slightly parallel to the equatorial plane of the tire. It has been found that there may be some improvement if used for belts at an angle, and efforts are being made to utilize this technique. However, with this type of belt structure, the rigidity of the belt is insufficient, resulting in inferior cornering force and camber thrust of the tire, resulting in inferior steering stability.

Therefore, the belt cord used as a reinforcing means for the tread portion is a helical cord molded in a spiral shape at a constant pitch, and the elongation of the cord is regulated to provide a radial tire that improves tire durability, handling stability, and riding comfort. is the object of the present invention.

[Means to solve the problem]

In order to solve the above problems, the pneumatic radial tire of the present invention has a carcass with a radial structure that is folded back around the beat core of the beat part from the tread part through the sidewall part, and a carcass that is radially outside of the carcass and inside the tread part. The first belt layer includes a single strand belt cord made by twisting at least two metal filaments and forming a helical pattern with a pitch (P) of 10 to 20III1 with a topping rubber. In addition, the belt cord of the earlier model has an elongation of 1.5% or more when a load of 5 kg is applied to each cord before being covered with the topping rubber, and an elongation of 3.5% when a load of 20 kg is applied. It is set to be 0 or less.

The topping rubber has a 50% modulus of 10 kg.
/d or more and 40 kg/cgi or less.

[Effect]

Unlike conventional cords, the belt cord, which is a single-strand cord made of twisted filaments and shaped into a spiral shape, exhibits a low elastic modulus that increases the elongation rate in low load areas, and has a low elongation rate in high load areas. It has a non-linear elongation characteristic showing a high modulus of elasticity, and in particular, the elongation at a load of 5 kg is 1.5% or more and the elongation at a load of 20 kg is 3.0% or less.

Therefore, in a tire using such a belt cord, the belt layer is stretched in a well-balanced manner together with the carcass during internal pressure filling, and the belt layer has a high elongation and an increased elastic modulus, so that it has a hoop effect and is properly stretched. Holds the tire in a correct profile.

In addition, since the belt cord has non-linear elongation characteristics as described above, its elastic modulus can be increased in response to high tire external forces that act during cornering, braking, etc., and the amount of tire deformation can be reduced excessively. Improves handling stability by providing sufficient drag without increasing the force.

In addition, during normal running, the high elongation rate and low elastic modulus improve riding comfort, and since the belt cord is shaped in a spiral, stress concentration at the belt ends is alleviated and separation is suppressed.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the pneumatic radial tire of the present invention will be described below with reference to the drawings, taking as an example a case where the pneumatic radial tire of the present invention is a tire for a motorcycle.

In the figure, a tire 1 includes a tread portion 2 and sidewall portions 3 extending inward in the tire radial direction from both sides of the tread portion 2.
and a bead portion 4 located inside the sidewall portion 3 in the tire radial direction, and a toroidal carcass that passes through the sidewall portion 3 and the tread portion 2 between bead cores 5 provided in the bead portion 4. 6 is spanned over, and a belt layer 9 is arranged on the radially outer side of the forceps 6 and on the inside of the tread portion 2 .

The tread portion 2 extends from the center of the crown toward both ends on the crown of the carcass 6 substantially parallel to its contour, and has a cross-sectional shape whose linear width exceeds the maximum width of the sidewall portion 3.

In this example, the carcass 6 is made of a single layer of braai, the cord of which is inclined at an angle of about 70 to 90 degrees with respect to the tire circumferential direction, and is a folded cord that is folded around the bead core 5 from the inside to the outside. By terminating the end 6a at the sidewall portion 3, lateral rigidity is improved. Note that when the cord angle is 70 degrees or less, it is difficult to obtain the excellent high-speed running characteristics that are characteristic of radial tires.

Note that the carcass 6 may be formed using a plurality of plies.

Next, as the ply cord of the carcass 6, a highly extensible organic fiber cord having a tensile modulus, particularly an initial modulus of elasticity of 1,500 kgf/mm" or less, such as rayon or polyester, is used. Preferably, nylon fiber cords are used.

In addition, the belt layer 9 is formed from two belt blazers 9A and 9B in this example, which go around in the tire circumferential direction approximately parallel to the crown contour of the carcass 6, and the belt blazer maximum width BW along the belt layer 9 is By making the tread width TW 0.75 times or more along the tread surface, the tread portion 2 is reinforced with a hoop effect over almost the entirety thereof.

In addition, the belt brakes 9A and 9B are 3 points relative to the tire equator.
It is formed by covering belt cords 10-1 arranged at an angle of 5 degrees or less with topping rubber 13.

In the present invention, as shown in FIG. 3, the belt cord 10 includes at least two metal filaments, in this example four steel filaments 11-
A single strand 12 with a 1×4 structure made by twisting each other and attaching rubber is used, and its pitch length P is 10 to 20 m.
The belt cord 10 has an elongation S when a load of 5 kg is applied to each belt cord 10 before being coated with the topping rubber.
8 is set to be 1.5% or more and the elongation S so at a load of 20 kg is set to 3.0% or less.

The above-mentioned elongation can be obtained by appropriately setting the filament diameter, helical pitch, etc., but the helical pitch P is as described above (preferably 10 to 20 mm. If the elongation is 20 mm or more, the steel cord will be damaged due to dynamic repeated compression movements during use of the tire. It is easy to cause buckling fatigue.Furthermore, it is susceptible to cut damage caused by stones stepping on it while running.Furthermore, if it is smaller than 10 mm, the productivity during cord manufacturing will be significantly lowered, causing a problem in terms of profitability.

The belt cord 10 shaped in this way has a large elongation at low loads, and the elongation rate decreases as the load increases, as shown by curve B in Figure 4 compared with the conventional belt cord A. It has non-linear elongation characteristics.

Therefore, by using the belt cord 10 with this elongation characteristic, the belt layer is stretched in a well-balanced manner together with the carcass during the internal pressure filling process, and eventually the elongation becomes high and the elastic modulus increases, thereby creating a hoop effect and an appropriate profile. Hold tire 1 at .

Furthermore, since the belt cord 10 has such non-linear elongation characteristics, its elastic modulus can be increased in response to large external forces that act on the tire during cornering, braking, acceleration, etc. , it is possible to provide sufficient drag without excessive tire deformation and improve steering stability.

During normal running, riding comfort can be improved due to the high elongation rate and low elastic modulus, and durability can be improved by alleviating stress concentration at the belt ends and suppressing separation.

If the elongation S8 is less than 1.5%, the stress concentration at the belt ends cannot be sufficiently alleviated, causing separation, resulting in poor durability and poor riding comfort. Also elongation S2. If it exceeds 3.0%, it will not be able to exert sufficient resistance against external forces, resulting in insufficient rigidity, impairing steering stability and causing uneven wear.

In order to fully exhibit such characteristics, it is necessary to cover the belt cord 1 with the topping rubber 13.
It is necessary to maintain the elongations S5 and S20 of 0 in a range of 90% or more at breakage, therefore, the topping rubber 1
3 has a 50% modulus of 10 kg/cm2 or more and 4
A material with high extensibility and softness with a weight of 0 kg/cm2 or less is used. Note that the 50% modulus is 10 kg/c
If it is less than m2, the strain at the end of the steel cord will increase,
Belt edge separation is more likely to occur. Also 4
If the weight exceeds 0 kg/cd, the durability of the belt cord, that is, cord breakage is likely to occur, and workability is also significantly reduced.

In addition to the motorcycle tires shown in this embodiment, the belt cord 10 having such characteristics can be suitably used in various tires that particularly require strong envelope characteristics, such as all-terrain four-wheel tires. I can do it.

〔Concrete example〕

A motorcycle tire without the structure shown in Figure 1 and with a tire size of 130/80R18 based on the specifications in Table 1 was manufactured as a prototype, and the durability of the tire was tested by a drum test, as well as handling stability, riding comfort, etc. was measured by actual vehicle driving tests.

Test method 1) High speed durability Load: 200 kg, internal pressure: 2.25 ksc, using a 60 inch diameter drum, from an initial speed of 150 kg/H, the speed at which standing waves are generated at a step speed of 10 kg/H every 10 minutes. Check visually.

2) Durability Tested at 150% of planned maximum load, internal pressure of 2.90ksc, and speed of 65km/H on a 60 inch diameter drum.

3) Vibration generation speed test A rider evaluated the speed at which vibrations occurred while driving on an expressway.

4) Steering stability (1) Test rider's feeling test on the test course (2) Cornering power test at 8° slip angle 5) Ride comfort On a rotating drum with trapezoidal protrusions attached to the surface, A vehicle equipped with the test tires was installed, the tires were rotated, and the unsprung vertical acceleration of the tires was measured. The maximum vibration value is determined from the waveform of the vibration over the protrusion and is displayed as an index. The larger the index, the better.

〔Effect of the invention〕

As mentioned above, the pneumatic radial tire of the present invention uses a helical cord formed in a spiral pattern at a constant pitch, and the pneumatic radial tire has a weight of 5 kg.
Since the elongation under load is 1.5% or more and the elongation under 20kg load is 3.0% or less, separation can be suppressed and durability can be improved, as well as ride comfort, handling stability, etc. .

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing a belt bridle, FIG. 3 is a perspective view showing a belt cord, and FIG. 4 is a diagram showing cord characteristics. 2-}Red part, S-. ．． −． side wall section,
4-bead portion, 5-...bead core, 6-.
−． ．．・Carcass, 9-. ．． ．． Belt layer, 9A, 9B
--Belt Bligh, 10-. ．． Belt cord, 11-. ．． ．． ．． Filament, 13-11 topping rubber.

Claims (1)

[Scope of Claims] 1. A carcass with a radial structure that is folded back around a bead core of a bead portion from a tread portion through a sidewall portion, and a belt layer disposed on the outside of the carcass in the radial direction and inside the tread portion. In addition, the belt layer has a belt ply in which a single-strand belt cord made of at least two metal filaments twisted together and spirally shaped with a pitch (P) of 10 to 20 mm is covered with topping rubber, and The belt cord is a pneumatic radial tire with an elongation of 1.5% or more when a load of 5 kg is applied and an elongation of no more than 3.0% when a load of 20 kg is applied to each belt cord before coating with topping rubber. . 2 The topping rubber has a 50% modulus of 10 kg
2. The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire has a weight of at least /cm^2 and at most 40 kg/cm^2.