GB2120178A

GB2120178A - Pneumatic radial or semi-radial tire for two-wheeled vehicle

Info

Publication number: GB2120178A
Application number: GB08310957A
Authority: GB
Inventors: Shinichiro Ohkuni; Shinichi Tamada
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1982-04-23
Filing date: 1983-04-22
Publication date: 1983-11-30
Also published as: GB8310957D0; GB2120178B; JPS58160807U

Abstract

The tire (1) comprises a tread portion (3) defining the maximum width of the tire and having a substantially constant thickness, a pair of sidewall portions (2), a pair of bead portions, a carcass (4) of radial or semi-radial structure (i.e. with cords at 50 DEG -90 DEG to mcp) composed of at least one rubberized organic cord ply (4-1, 4-2), and a belt (7) having at least one layer (7-1, 7-2) of cords with a modulus of elasticity of at least 600 kgf/mm<2> arranged at an angle of not more than 30 DEG with respect to the equatorial plane (0-0) of the tire. The carcass plies are wound around bead rings (5) from the inside toward the outside to form turn-up portions (6-1, 6-2), and a stiffener including a tapered rubber filler (8) having a Shore A hardness of at least 60 DEG is provided. The sidewall portion (2) has a rubber thickness of 4-8 mm at the maximum width position (P) of the carcass. <IMAGE>

Description

SPECIFICATION Pneumatic tire for two-wheeled vehicle This invention relates to a pneumatic tire for a two-wheeled vehicle, and more particularly to a pneumatic tire for a two-wheeled vehicle having a carcass of radial or semi-radial structure.

In general, radial tires have such a structure that a carcass is composed of one or a few rubberized plies each containing fiber cords or metal cords therein, the cords being arranged in a direction perpendicular to the equatorial plane of the tire (i.e. in a radial direction), and a belt arranged between the carcass and the tread portion is composed of a plurality of inextensible cord layers each containing metal cords arranged parallel with or inclined at a small angle with respect to the equatorial plane of the tire, the cords of which being crossed with each other.

Moreover, tires having a structure that the carcass in the above structure is composed of a plurality of rubberized plies each containing cords inclined at an angle of about 75 with respect to the equatorial plane of the tire, the cords of which being crossed with each other, are referred to as semi-radial tires in order to distinguish them from the radial tires.

Generally, it is well-known that the radial and semi-radial tires exhibit excellent performances such as high-speed durability, wet skid resistance, and road-gripping property because the belt serves to give a higher rigidity in the crown portion of the carcass as compared with the usually used bias tires (i.e. tires having a structure that the carcass is composed of a plurality of rubberized plies each containing fiber cords inclined at an angle of about 35 with respect to the equatorial plane of the tire, the cords of which being crossed with each other). This is applicable only as far as tires for four-wheeled vehicles are concerned.

When a carcass of radial or semi-radial structure as described above is applied to tires for twowheeled vehicles or motorcycles, however, the stiffness of the tire sidewall portion becomes relatively weak owing to the strong road-gripping force especially in an inclined state, which causes difficulties as regards steering stability. Therefore, little practical application of the radial or semi-radial carcass structure to tires for two-wheeled vehicles has taken place up to now.

The present invention aims to improve the stiffness of the sidewall portion, which is a factor causing unstable steering of radial and semi-radial carcass structures of tires for two-wheeled vehicles.

The present invention provides a pneumatic tire for a two-wheeled vehicle, comprising a tread portion of substantially constant thickness extending over a region defining the maximum width of the tire, a pair of sidewall portions extending inwardly from both ends of the tread portion, a pair of bead portions at the inner edges of the said sidewall portions, a carcass reinforcing the said portions and composed of at least one rubberized cord ply containing organic fiber cords arranged at an angle of 50"-90" with respect to the equatorial plane of the tire, and a belt disposed between the tread portion and a crown region of the carcass and composed of at least one cord layer containing cords with a modulus of elasticity of at least 600 kgf/mm2 arranged at an angle of not more than 30 with respect to the equatorial plane of the tire, wherein both end portions of at least one rubberized cord ply constituting the carcass are wound around bead rings at the said bead portions from the inside towards the outside in the direction of the rotational axis of the tire to form turn-up portions, and a stiffener comprising a tapered rubber filler having a Shore A hardness of at least 60 is disposed from an upper part of the said bead ring toward the tread portion, and the sidewall portion has a rubber thickness of 4-8 mm at a position corresponding to the maximum width of the carcass.

In the pneumatic tire according to the invention, the tread portion reinforced with the carcass necessarily extends over a region corresponding to the maximum width of the tire in view of its running performance. When the radial or semi-radial carcass structure is used as a reinforcement for the tread portion as well as the sidewall portion, the tread portion is further reinforced with the belt. In this case, the cords to be used in the belt necessarily have a modulus of elasticity of not less than 600 kgf/mm2.Moreover, in order to improve the weak stiffness of the sidewall portion, it is necessary that both end portions of at least one rubberized cord ply constituting the carcass are wound around bead rings located in the bead portions from the inside toward the outside in the direction of the rotational axis of the tire to form turn-up portions and further a stiffener comprising a tapered rubber filler having a Shore A hardness of at least 60 is disposed from an upper part of the bead ring toward the tread portion, and further the thickness of the sidewall portion is 4-8 mm, preferably 5-7 mm, at a position corresponding to the maximum width of the carcass.

The invention will be further described, by way of example only, with reference to the accompanying drawing, which is a radial half section of an embodiment of a pneumatic tire for a motorcycle according to the invention.

In the single figure is shown a radial half section of an embodiment of a pneumatic tire 1 for a motorcycle according to the invention. While only the right half section of the tire 1 is illustrated with respect to an equatorial plane 0-0 of the tire, it is to be understood that the half not illustrated corresponds to that illustrated.

The tire 1 comprises a pair of bead portions, a pair of sidewall portions 2 and a tread portion 3, these portions being connected toroidally to each other. The sidewall portion 2 and the tread portion 3 are reinforced with a carcass 4 as a whole. The tread portion 3 extends along the carcass at a substantially constant thickness over a region between side edges e of the tread portion defining the maximum width of the tire. A position P indicates the maximum width of the carcass 4. That is, the maximum width position of the carcass 4 is a region not reinforced with a stiffener 8 or a cord reinforcing layer 9 but reinforced with only the coating rubber for the sidewall portion 2. Therefore, the coating rubber used has a Shore A hardness of 50 to 65 .

In the maximum width position of the carcass, the thickness t of the sidewall portion is within a range of 4-8 mm, preferably 5-7 mm. In the illustrated embodiment, the thickness of the sidewall portion is 5 mm. When the thickness t is less than 4 mm, the stiffness of the sidewall portion is too weak, while when the thickness t exceeds 8 mm, there are caused difficulties in regards heat generation and vibration of the tire.

In the illustrated embodiment, the carcass 4 is composed of two rubberized cord plies 4-1 and 4-2, both end portions of which are wound around bead rings 5 located at radially inner edges of the sidewall portions 2 from the inside toward the outside in the direction of the rotational axis of the tire to form turn-up portions 6.

The carcass 4 is composed of one or several rubberized cord plies each containing organic fiber cords such as nylon, rayon, or polyester arranged at an angle of 50 -90 with respect to the equatorial plane 0-0, both end portions of at least one cord ply of which are wound around the bead rings 5 toward the outside in the direction of the rotational axis of the tire to form the turn-up portions 6. In the illustrated embodiment, the carcass 4 is composed of two cord plies 4-1 and 4-2, each of which is wound outwardly around the bead ring 5 to form a lower turnup portion 6-1 and a higher turn-up portion 6-2, respectively.

A belt 7 is disposed on a crown region C of the carcass beneath the tread portion 3 for reinforcing the crown region C of the tread portion. In this case, both ends of the belt 7 may somewhat extend beyond the side edges e of the tread portion 3 into the side wall portion 2, but it is preferable to terminate both ends of the belt 7 short of the side edges e of the tread portion as shown in the drawing. The belt 7 is composed of at least one cord layer containing cords with a modulus of elasticity of at least 600 kgf/mm2 arranged at an angle of not more than 30 with respect to the equatorial plane 0-0. When the belt 7 is composed of a plurality of cord layers, the cords of these layers are crossed with each other at an angle of 15"-30" with respect to the equatorial plane or arranged substantially parallel with the equatorial plane.

The term "modulus of elasticity" of cord to be used in the belt is defined by Ec calculated by the following equation when a relation between load and elongation is measured by applying a tensile force to the cord and a rising slope of the measured load-elongation curve is extended from this curve to determine a load F (kgf) at 10% elongation: Fox 10 Ec= - S F is the load at 10% elongation and wherein S is the sectional area (mm2) of the cord.

In this connection, the modulus of elasticity of some conventionally known cords is exemplified as follows: Nylon-6 285 kgf/mm2 Nylon-66 345 kgf/mm2 polyester 456 kgf/mm2 High-modulus polyester*' 600 kgf/mm2 Rayon 650 kgf/mm2 Kevlar*2 3,700 kgf/mm2 Steel 16,000 kgf/mm2 *1: cord of low polymerization degree polyethylene terephthalate having an intrinsic viscosity of 0.3-0.8 as measured in a solvent of o-chloro-phenol at a temperature of 25"C; *2: trade name of aromatic polyamide fiber cord, made by Du Pont Nemours, E.l; "Kevlar" is a Registered Trade Mark.

In the illustrated embodiment, the belt 7 is composed of two cord layers 7-1 and 7-2. Metal cords or fiber cords may be used alone in both the layers 7-1 and 7-2, or fiber cords may be used in the layer 7-1 and metal cords in the layer 7-2, or metal cords may be used in the layer 7-1 and fiber cords in the layer 7-2. In any case, at least one cord layer constituting the belt must have a modulus of elasticity of cord of not less than 600 kgf/mm2.

As the metal cord, it is desirable to use steel cord obtained by twisting 6 to 25 steel filaments, each having a diameter of not more than 0.15 mm, more preferably not more than 0.1 2 mm, with each other. Practically, the diameter of the steel filaments may be 0.1 5 mm, 0.1 2 mm or 0.10 mm. Furthermore, when metal cord is used in the cord layers for the belt, it is preferable to arrange the metal cords at a spacing ratio of 35-65%, and in this case the flexural rigidity of the cord in the thickness direction of the belt is not increased excessively. The spacing ratio of metal cords is defined by the following equation: f-d Spacing ratio = /f X 100 (%) wherein f is the distance between the cord centres and d is the diameter of the cord.

In the illustrated embodiment, a tapered rubber filler 8 extending from the upper part of the bead ring 5 toward the tread portion 3 is disposed as a stiffener between the carcass 4 and the turn-up portion 6 thereof. The rubber filler has a Shore A hardness of at least 60 , preferably not less than 65 . The upper limit of the hardness is not critical in view of the tire performance, but when the hardness is higher than about 98 , the working efficiency becomes undesirably poor in view of tire production.

As the stiffener, there is preferably used a composite structure of a rubber filler and a cord reinforcing layer 9 arranged along the rubber filler from the upper part of the bead ring 5 toward the tread portion 3. In the cord reinforcing layer 9, the fiber or metal cords are arranged at an inclination angle of 15"-30" with respect to a tangent of a concentric circle of the tire passing a radially inner end of the cord reinforcing layer 9 at an intersection of the circle with the cord of the layer 9. The cord reinforcing layer 9 may be arranged alone or together with the rubber filler outside the turn-up portion 6 in its axial direction.However, it is desirable to arrange the cord reinforcing layer 9 together with the rubber filler between the carcass 4 and the turn-up portion 6 thereof so as to adjoin the cord reinforcing layer 9 to the turn-up portion 6 was shown in the drawing.

When radial heights extending from the bead base b in the tread direction to the ends of the rubber filler 8, turn-up portions 6, particularly turn-up portion 6-2, and cord reinforcing layer 9 are ho, h1 and h2, respectively and the height of the sidewall portion expressed by the radial distance from the bead base b to the side edge e of the tread portion 3 is h, at least one of heights h,, h, and h2 is preferably at least 60% of the height h of the sidewall portion.

Furthermore, it is desirable that at least one of the height h0 of the rubber filler and the height h2 of the cord reinforcing layer 9 is within a range of 50-75% of the radial height h of the sidewall portion.

In the drawing, reference numeral 11 is a chafer composed of fiber cords or a woven fabric serving to prevent rim chafing and to reinforce the lower part of the sidewall portion.

Four radial tires (Tires A-D) and three semi-radial tires (Tires E-G) were manufactured together with conventional radial tires (Control tires No. 1 and No. 2) according to tire dimensions as shown in the following Table. Each of these tires was actually run on a circuit course of 4.3 km at a maximum speed of 200 km/hr, during which susceptibility to disturbance (weak stiffness feeling) was evaluated by the driver to obtain a result as shown in the table, wherein the weak stiffness feeling is indicated by an index for steering stability on the basis that the control tire is 1 00.

Moreover, the control tire had a size of 3.00 H 1 9 for the front wheel and 4.00 H 1 8 for the rear wheel, while each of the tires A-G had a size of 90/80-19 for the front wheel and 120/80-18 for the rear wheel. In these tires, the internal pressure was 2.0 kg/cm2 for the front wheel and 2.2 kg/cm2 for the rear wheel, respectively.

Control tire Invention tire

No.1 No.2 A B C D E F G Tread with 150 mm # # # # # # # # steel steel Kevlar steel steel Kevlar steel filament filament 1,5000d/2 filament filament 1,500d/2 filament cord material 0.25 mm# # 0.12 mm# # 0.12 mm # 0.12 mm# 0.12 mm# 1 x 5 3 x 4 3 x 4 3 x 4 # 3 x 4 Belt cord angle 20 # 0 20 # # # # # width W1 of layer 7-1 120 mm # # # 175 mm 120 mmm # 175 mm 120 mm width W2 of layer 7-2 100 mm # -- 100 mm # # # # # Sidewall thicknesst 2.5 mm # 6.0 mm # # # # # # portion height h 73 mm # # # # # # # # polyester cord material 1,500d/2 # # # # # # # # (2 plies) Carcass cord angle 90 75 90 # # # 75 # # height h1 of turnup 30 mm # # # # # # # # Kevlar kevlar Cord rein- cord material angle -- -- -- -- -- 1,500d/2 -- -- 1,500d/2 forcing 20 20 layer height h2 -- -- -- -- -- 45 mm -- -- 45 mm Rubber hardness 62 # # # # # # # # filler height h0 35 mm # # # # # # # # Effect (weak stiffness feeling) 100 97 90 90 84 84 87 81 81 As apparent from the table above, the steering stability is considerably improved in the tires according to the invention as compared with the control tires, from which it can be seen that, according to the invention, the radial or semi-radial carcass structure can advantageously be applied to pneumatic tires for motorcycles.

The tires according to the invention suitably have an aspect ratio of not more than 86%, i.e.

the ratio of the tire height to the maximum tire width.

Claims

1. A pneumatic tire for a two-wheeled vehicle, comprising a tread portion of substantially constant thickness extending over a region defining the maximum width of the tire, a pair of sidewall portions extending inwardly from both ends of the tread portion, a pair of bead portions at the inner edges of the said sidewall portions, a carcass reinforcing the said portions and composed of at least one rubberized cord ply containing organic fiber cords arranged at an angle of 50"-90" with respect to the equatorial plane of the tire, and a belt disposed between the tread portion and a crown region of the carcass and composed of at least one cord layer containing cords with a modulus of elasticity of at least 600 kgf/mm2 arranged at an angle of not more than 30e with respect to the equatorial plane of the tire, wherein both end portions of at least one rubberized cord ply constituting the carcass are wound around bead rings at the said bead portions from the inside toward the outside in the direction of the rotational axis of the tire to form turn-up portions, and a stiffener comprising a tapered rubber filler having a Shore A hardness of at least 604 is disposed from an upper part of the said bead ring toward the tread portion, and the sidewall portion has a rubber thickness of 4-8 mm at a position corresponding to the maximum width of the carcass.

2. A pneumatic tire as claimed in claim 1, wherein cords of the carcass are arranged in a direction substantially perpendicular to the equatorial plane of the tire.

3. A pneumatic tire as claimed in claim 1, wherein the carcass is composed of at least two rubberized cord plies, the cords of which are crossed with each other at an angle of 60"-80" with respect to the equatorial plane of the tire.

4. A pneumatic tire as claimed in any of claims 1 to 3, wherein cords of the belt are arranged substantially parallel with the equatorial plane of the tire.

5. A pneumatic tire as claimed in any of claims 1 to 3, wherein the belt is composed of two cord layers, the cords of which are crossed with each other at an angle of 15"-30" with respect to the equatorial plane of the tire.

6. A pneumatic tire as claimed in claim 5, wherein the belt is composed of two metal cord layers.

7. A pneumatic tire as claimed in claim 5, wherein the belt is composed of two fiber cord layers.

8. A pneumatic tire as claimed in claim 5, wherein the belt is composed of one metal cord layer and one fiber cord layer.

9. A pneumatic tire as claimed in any of claims 1 to 6, wherein cords of the belt are obtained by twisting 6 to 25 steel filaments, each having a diameter of not more than 0.15 mm, with each other.

10. A pneumatic tire as claimed in claim 9, wherein the cords of the belt are obtained by twisting 6 to 25 steel filaments, each having a diameter of not more than 0.12 mm, with each other.

11. A pneumatic tire as claimed in any of claims 1 to 10, wherein the said stiffener is a composite structure of the said rubber filler and at least one cord reinforcing layer containing cords arranged at an inclination angle of 15"-30" with respect to the circumferential direction of the tire.

1 2. A pneumatic tire as claimed in claim 11, wherein at least one of the radial heights extending from the bead base in the tread direction to the ends of the said rubber filler, the said cord reinforcing layer and the said turn-up portion of the carcass is at least 60% of the radial height of the said sidewall portion measured from the bead base.

1 3. A pneumatic tire as claimed in claim 11, wherein at least one of the radial heights extending from the bead base in the tread direction to the ends of the said rubber filler and cord reinforcing layer is 50%-75% of the radial height of the said sidewall portion measured from the bead base.

1 4. A pneumatic tire as claimed in any of claims 1 to 13, wherein the said sidewall portion has a rubber thickness of 5-7 mm at a position corresponding to the maximum width of the carcass.

15. A pneumatic tire as claimed in any of claims 1 to 14, having an aspect ratio of not more than 86%.

1 6. A pneumatic tire according to claim 1, substantially as herein described with reference to, and as shown in, the accompanying drawing.