JPH03189214A - Pneumatic radial tire for heavy duty service - Google Patents

Abstract

PURPOSE:To suppress ply cord fatigue and improve comfort of sitting in a car cabin by securing the small wall thickness range at each side part over a wide extent as 50% of the internal surface max. height of the tire, and thereby enlarging the deformable range of the side part. CONSTITUTION:In a radial tire concerned, the internal surface max. height from the rim dia. line l is represented by H, while the intersecting point of a straight line l1 in parallel with the tire rotational axis, being H/2 apart from the rim dia. line l, with the tire internal surface is designated as P1. Further P2 and P3 are intersecting points of two parallel straight lines l2, l3, being h1 apart from the first named straight line l1 to the rim side and h2 apart to the opposite side, with internal surface of the tire. Therein t1+t2+t3 shall lie within the extend 32-38 mm, where t1 thru t3 represent the tire thicknesses in the normal direction at these intersecting points P1-P3, and t2/t1 shall be set within the range 1.8-2.5 while t3/t1 within 1.4-2.0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heavy-duty pneumatic radial tire used for large vehicles such as trucks and buses.

[Prior art and problems to be solved by the invention] In heavy-duty pneumatic radial tires for large vehicles such as trucks and buses that use steel cord for the carcass ply, the flatness ratio has been changed to lower the vehicle floor. It is known that the ratio is reduced to 80% or less. In conventional tires of this type, as the tire height decreases due to flattening, the range in which the wall thickness of the side part is small becomes narrower, and therefore the range in which the side part can be deformed becomes smaller.

Now, if a large bending deformation occurs in a narrow range of the side portion when the tire is in a run-flat state under low internal pressure such as during banking, a small radius deformation occurs in the bridle cord of this side portion.

Therefore, the fatigue of the braai cord in the side portions is large, and cord breakage may occur.

Furthermore, since the deformation range of the side portions is small, vibrations generated when the tire runs over an obstacle on the road surface are poorly absorbed, resulting in poor riding comfort.

The present invention has been made in view of the above circumstances, and provides a heavy-duty pneumatic radial tire that suppresses fatigue of the bridle cord in the side part and improves riding comfort by expanding the deformable range of the side part. The purpose is to provide.

[Means for Solving the Problems] The heavy-duty pneumatic radial tire according to the present invention is a pneumatic radial tire that uses steel cord for the carcass ply and has an aspect ratio of 80% or less. The maximum height of the inner surface of the tire from the rim diameter line ρ in the filled state is defined as H, and the intersection of the inner surface of the tire with a straight line g1 parallel to the axis of rotation of the tire and distance H/2 from the rim diameter line Ω is defined as Pl. Distance h1 from straight line g1 to the rim side, h2 to the opposite side (however, hl/H=0.
16 h2/H=0.34. ) are two other straight lines Ω2 parallel to the straight line g1. The intersections of Ω3 and the inner surface of the tire are respectively designated as P2. P3, points PL, P2 and P3
When the tire thicknesses in the normal direction to the inner surface of the tire are t1, t2, and t3, respectively, tl + t2
+t3 is 3' 2 mm or more and 38 mm or less, and t
2/t1 is 1.8 or more and 2.5 or less, and t
3/t1 is set to 1.4 or more and 2.0 or less.

[Function] In the heavy-load pneumatic radial tire according to the present invention, at least 50% (hl + h2
) has a small wall thickness on the side.

If 11 +t2 +t3 exceeds 38 mm, the rigidity of the side portions will increase, making it impossible to improve the fatigue resistance of the bridle cord and the ride comfort. Conversely, if tl + t2 + t3 is less than 32 mm, the required side part rigidity cannot be obtained.

The same applies when t2/t1 and t3/t1 are out of the above range.

[Example] FIG. 1 is a half-sectional view of a heavy-duty pneumatic radial tire according to an example of the present invention.

This tire has a size of 285/75R24.5, and a steel cord is used for the carcass ply (not shown) extending from the tread portion 2 through the side portions 4 to the bead portions 6. Let H be the maximum height of the inner surface of the tire from the rim diameter line g when a regular rim is filled with air to the regular internal pressure. The half height of this tire, i.e. the rim diameter line g
A straight line g1 parallel to the tire rotation axis is assumed at a position a distance H/2 away from , and the intersection of this straight line 91 and the inner surface of the tire is Pl. Another straight line parallel to the straight line Ωl is located at a height a distance hi (hl/H=0.16) from the straight line g1 toward the rim! 12, and let the intersection of this straight line g2 and the inner surface of the tire be P2. straight line 1
1 to the opposite side of the rim, that is, the distance h2 to the outside in the radial direction.
Assuming yet another parallel straight line g3 separated by (h2/H=0.34), the intersection of this straight line 113 and the inner surface of the tire is defined as P3.

When the tire thicknesses in the normal directions to the inner surface of the tire at the points PL, P2, and P8 determined as described above are respectively t1, t2, and t3, the tire of this example has the following formula: tl-8,0 mm t2 = 17 .5 mrn t3 = 12.0 mm.

At this time, t1, +t2 +t3-37.5romt2/t1
−2,1 t3 /t1 −1,5.

Regarding the heavy-duty pneumatic radial tire (Example 1) according to the embodiment of the present invention described above, a low internal pressure running test was conducted to measure the mileage until the ply cord broke, and the tire was filled with the specified internal pressure. The longitudinal spring constant was measured at

The measurement results are shown in Table 1. However, the conditions for the low internal pressure running test are as follows.

Drum diameter: 1707mm Rim size: 8.25X24° Internal pressure: 2. 0kg/cm2 Load: 0.88 times the specified speed: 25-30 km/h (margins below) The results are also shown. Comparative Example 1 is a conventional tire. However, Example 1.2 and Comparative Example 5~
Since ply cord breakage did not occur in Tire No. 12, the evaluation was terminated at the time when cracks occurred in the side portions.

As shown in the table, in the tires of Examples 1 and 2, the fatigue resistance of the ply cords was significantly improved. Furthermore, since the longitudinal spring constant is small, riding comfort is improved.

[Effects of the Invention] As explained above, the heavy-duty pneumatic radial tire according to the present invention secures a small wall thickness at the side portion over a wide range of at least 50% of the maximum inner surface height H of the tire. Therefore, the deformable range of the side part is large. Therefore, according to the present invention, it is possible to provide a pneumatic radial tire for heavy loads that suppresses fatigue of the ply cords in the side portions and improves riding comfort.

[Brief explanation of drawings]

Here's a half-sectional view of my favorite radial tire. Explanation of symbols 2...Tread part, 4...Side part, 6 river bead part, H...Maximum height inside tire, P/Rim diameter Toyo Tire & Rubber Industries, Ltd.

Claims (1)

[Claims] 1. A pneumatic radial tire that uses steel cord for the carcass ply and has an aspect ratio of 80% or less, where H is the maximum height of the inner surface of the tire from the rim diameter line l when the tire is filled with air to the regular internal pressure using a regular rim. The intersection point of the inner surface of the tire and a straight line l1 parallel to the tire rotation axis separated by a distance H/2 from the rim diameter line l is defined as P1, and this straight line l1
Distance h1 from the rim side, h2 to the opposite side (however, h1/
Let H=0.16 and h2/H=0.34. ) The intersection points of the inner surface of the tire with two straight lines l2 and l3 parallel to the straight line l1 separated by a distance of 100 mm are respectively P2 and P3, and the tire thicknesses in the normal direction to the inner surface of the tire at points P1, P2 and P3 are t1 and 1, respectively. When t2 and t3, t1+
t2+t3 is 32 mm or more and 38 mm or less, and t2
/t1 is 1.8 or more and 2.5 or less, and t3/t
A pneumatic radial tire for heavy loads, characterized in that 1 is 1.4 or more and 2.0 or less.