JPS61202901A - Radial tire for passenger car - Google Patents

Abstract

PURPOSE:To reduce rolling resistance without causing earlier wear around a shoulder by suitably contriving the form of a round shoulder between both ends of a tread and side wall parts while specifying a ground contacting rectangle ratio. CONSTITUTION:In a pneumatic tire,a carcass 1 having arranged fiber cords which extend into the surface of the radius of a tire, and a belt 2 surrounding the crown area of the carcass 1, are reinforced for a tire body. The both ends of a tread part 3 are smoothly connected to side wall parts 4 via round shoulders 5. The round shoulder 5 is formed by a circular arc C which is inscribed in the outer contour curves C1, C2 of the parts 3, 4. The intersecting angle theta of common tangential lines l1, l2 at the inscribed points P, Q on the both ends of the arc C, is set at 35 to 40 deg.. Also, the ratio of ground contacting length l at a position 40% the ground contacting width W apart from a equator, to a ground contacting length L at the equator (ground contacting rectangle ratio) l/L is set at 0.85 to 0.96.

Description

[Detailed Description of the Invention] (Industrial Application Field) Pneumatic radial tires, especially the types of tires used for passenger car transport, need to reduce burning costs by reducing rolling resistance. Conventional radial tires tend to have inferior ride comfort compared to conventional bias tires, so they must not be accompanied by this deterioration, and on the other hand, they must not be accompanied by deterioration in wear resistance.

The following describes the results of research and development aimed at reducing rolling resistance without compromising riding comfort or wear resistance.

(Prior art) Generally, radial tires for passenger cars have an internal pressure of 20 to 4
It is known that by increasing the strength by about 5%, the energy spent on deformation due to load transfer is suppressed and the rolling resistance is reduced. Although this method is simple and effective, it causes a deterioration in riding comfort, so it is not generally adopted, except for tires of a specific size or type.

On the other hand, attempts have been made to make the width of the belt embedded in the tread part narrower than the ground contact width of the tire.In this case, the internal pressure used does not increase, so it does not affect ride comfort, especially cornering characteristics. Although rolling resistance can be reduced without causing problems in handling stability, there is a disadvantage that early wear starting at the shoulders is accelerated as the overall wear of the tread portion progresses.

OBJECTS OF THE INVENTION It is an object of the invention to achieve an advantageous improvement in rolling resistance without premature wear in the shoulder region and, of course, without deterioration of ride comfort.

(Means for Solving the Problems) The present invention comprises a toroidal carcass of at least one ply in which the fiber cords are arranged in an array extending substantially within the radial plane of the tire; In a pneumatic tire, the body is reinforced with a belt made of non-stretchable cords, and the tread part reinforced with the belt in the crown area of the carcass is smoothly connected to the sidewall parts lined with the carcass through round shoulders at both ends. In addition, the round shoulder is made of a circular arc inscribed in each of the outer contour curves of the tread portion and the sidewall portion, and the mutual intersection angle of the common tangent lines at the inner contact points of both ends is within the range of 35 to 45 inches. , the tread contact area in the loading position of the specified load under the specified internal pressure filling,
The ratio of the contact length l at a position extending 40% of the contact width laterally from the equator to the contact length at the tire's equator position //L is in the range of 0.85 to 0.95. This is a radial tire for passenger cars characterized by having a rectangular ratio.

In the tire of the present invention, common fiber cords such as nylon, polyester, rayon, and even aromatic polyamide fibers are used as the carcass plies so as to extend substantially within the tire radial plane, that is, so-called radial fiber cords. In the arrangement, one or more plies, up to three brilies at most, can be used, and these plies are folded around the bead core in accordance with common practice, and a hard stiffener is placed between the fold and the carcass as appropriate. The required rigidity near the fold can be increased.

Regarding the belt, a rubberized layer is formed by arranging cords with high elastic modulus such as steel cords and aromatic polyamide fiber cords at a shallow angle of 15 to 25 degrees with respect to the tire's equatorial plane. It shall include two cross-layers with the .

This belt is arranged to wrap around the crown area of the carcass over a tread width of 95-105x, preferably 97-100x.

In a tire that uses the above carcass and belt for body reinforcement, according to custom, the tread part reinforced with the above belt in the crown area of the carcass is smoothly connected to the sidewall part lined with the carcass through round shoulders at both ends. It has a layered rubber outer skin.

Figure 1 shows a cross section of the above-mentioned radial tire in the internal pressure position after the rim assembly.

In the figure, 1 is a carcass, 2 is a belt, 3 is a tread portion, 4 is a sidewall portion, and 5 is a shoulder. Also 6
7 indicates a bead portion, 7 indicates a bead core, 8 indicates a rim, and 9 indicates a rim flange.

The shoulders 5 at both ends of the tread portion 3 include the tread portion 3 and sidewall portions 4 in addition to the round shoulders shown in the figure.
The so-called square 7 has an edge where both outer contours intersect.
Although there is a shoulder, when cornering at high speed, the tread contact area tends to float on the anti-returning force side, which tends to reduce the contact area and impair steering stability. Round shoulder tires are exclusively used for passenger cars.

Since reducing rolling resistance by increasing internal pressure has the disadvantage of impairing riding comfort, the inventors further investigated the conventional technique of reducing rolling resistance by reducing belt width.

That is, in this type of tire, the crown portion of the carcass 1 has a curved surface with a convex curvature outward in the radial direction of the tire, and the belt 2
Therefore, the tread portion 3 also has an outer surface shape similar to this, but on the other hand, the outer surface of the tread portion 3 is deformed to become virtually flat in the contact area under normal load, and in order to reduce energy loss due to deformation during this time, Eliminating the belt arrangement near the shoulder 5, where ground contact deformation is more pronounced, is nothing less than narrowing the width of the belt 2. As a result, the rigidity near the shoulder 5 decreases, causing early wear. It was.

On the other hand, in order to maintain cornering characteristics and steering stability during high-speed running, in the case of the round shoulder 5 having a relatively large radius of curvature, the contact width at the tread portion l increases significantly as the entire tread wears due to use of the tire.
As a result, the rigidity at the ground contact width end, that is, near the periphery of the shoulder 5 is further reduced, and wear of the shoulder 5 is accelerated.

As a result of conducting experiments and research based on this clarification, the present invention has improved the conventional practice of radial tires in terms of reinforcing the tread portion 3 with the belt 2 in the crown area of the carcass 1, and has therefore further strengthened the belt. Although measures such as width reduction were eliminated, the purpose of the invention could be appropriately achieved by specifically specifying the outer contour of the round shoulder and specifying the ground contact rectangular ratio in the tread contact area. .

Here, the outer contour of the round shoulder is defined by the outer contour curves C, , , of the tread portion and the sidewall portion 4, as shown in Fig. 2.
Each inscribed point P at both ends of the arc C inscribed in Ct,
Common tangent at Q1. , It2 are given by the arc C such that the intersection angle is 35 to 45 degrees, preferably around 40''. Note that both tangents 1..It.

The distance between the intersection point R and another similar intersection point generally gives the ground contact width W of the tread portion.

Next, regarding the ground contact rectangular ratio, as shown in Figure 3, the tread portion 3
40% of the contact width W from this equator position with respect to the contact length of the tire at the equator XX position assuming a contact shape f of
It is given by the ratio of the ground contact length i at the position where the ground is flattened, and it is essential that the value is in the range of 0.85 to 0.95.

(Function) Contact￥VAI1. If the intersection angle of lz exceeds 45'', smooth sliding will be hindered during sharp turns that are sometimes difficult to avoid while driving, resulting in deterioration of steering stability;
When the angle is smaller than 5°, the ground contact width tends to increase significantly due to wear of the tread portion 3, resulting in early wear of the shoulder due to a decrease in rigidity in the vicinity of the shoulder and its acceleration.

Regarding the ground contact rectangular ratio, less than 0.85 means that the contact length at the center of contact is excessive compared to both sides.
In other words, this means that the tread portion 3 is greatly deformed and the energy was wasted, which impairs rolling resistance.On the other hand, if it exceeds 0.95, there is no problem in terms of rolling resistance. In either case, the ground contact pressure at the shoulder 5 is increased and its movement is increased, and shoulder wear begins to occur.

Regarding the width of the belt 2, the width of the belt 2 does not exclude belt configurations that include additional layers in addition to the two crossed layers in the illustrated example, but it is determined by the width of the belt main layer that is responsible for the tension burden made of the crossed layers as shown in the figure. The narrower width 6 is preferably 97 to 100χ, rather than 95 to 105χ of the ground contact width W of the tread portion 3.
It is appropriate to do so.

If this width -6 is narrower than 95%, there is a concern that shoulder wear may occur due to insufficient rigidity in the shoulder region.

If it exceeds 105χ, an undesirable increase in rolling resistance is brought about and there is a looseness.

As described above, by matching both the outer contour shape of the round shoulder 5 and the ground contact rectangle ratio in the contact area of the tread portion 3, the rigidity near the periphery of the shoulder 5 is maintained and It is thought that the energy loss associated with the deformation of is minimized.

(Example) A steel cord (1 x 5 x 0.24 mm) was placed around the crown of a carcass using one piece of braai arranged in a radial arrangement of 1500 d/cm of polyester cord according to custom.
Two rubberized layers with slightly different widths are arranged at an inclination angle of 1B with respect to the equatorial plane of the tire, the narrower of which matches the tread width W, and the remaining on both sides slightly protrudes from the carcass. Regarding a passenger car tire of size 1655R13, which strengthens the body by placing a belt with the cords stacked in the opposite direction in the order along the crown,
The following table summarizes test results comparing the relationship between steering stability, shoulder wear, and rolling resistance by applying the configuration of the present invention.

The test conditions were as follows: regular 5J x 13 rims were used, the tire filling internal pressure was 1.9 kg/cut, and the wheel load was 425 kg.

In this test, for an example in which four ribs were divided into three circumferential grooves that divided the tread part 3 into four, the total tread wear that occurred in the tread part 3 was determined by the decrease in the groove depth in the central circumferential groove. For convenience, the difference between the groove depth through both side circumferential grooves and the level reduction amount is defined as the shoulder drop wear amount, and the performance with the conventional tire is 10.
The index was set to 0, which caused a hailstorm.

In addition, the driving stability was 80 to 15 on the test course.
We performed lane chain and slalom driving under conditions that simulated a slightly higher speed range than normal driving at a speed of 0 km/hr, and the test driver's feeling was that the conventional tire was 1. The following judgment was made.

Regarding rolling resistance, indoor steel drums (1, 6
After increasing the rotational speed to a circumferential speed equivalent to 2001 m), the clutch was disengaged and the determination was made based on a predetermined calculation based on the degree of deceleration during trailing rotation.

(Effect of the invention) The rolling resistance of a radial tire for a passenger car with a round shoulder is advantageously reduced without worrying about premature wear around the shoulder or its acceleration, and without deteriorating ride comfort. be able to.

[Brief explanation of the drawing]

Figure 1 is a sectional view, Figure 2 is a detailed view of the main parts, and Figure 3 is a schematic diagram of the ground contact shape. 1...Carcass 2...Belt 3...Tread part 4...Side wall part 5...Round shoulder Figure 1 Figure 2 Figure 3 ×

Claims (1)

[Scope of Claims] 1. A toroidal carcass of at least one ply having a fiber cord arrangement extending substantially within the radial plane of the tire, and a belt of non-stretchable cords surrounding the crown area of the carcass. In a pneumatic tire that has body reinforcement and a tread part reinforced with the belt in the crown area of the carcass, and sidewall parts lined with the carcass connected smoothly through round shoulders at both ends, the round shoulder is The tread portion and the sidewall portion are composed of circular arcs inscribed in each outer contour curve, and the mutual intersection angle of common tangent lines at the internal contact points at both ends is 35 ~
In addition to the outer contour being within the range of 45°,
The ratio of the contact length L at the position where 40% of the contact width is deviated laterally from the equator to the contact length L at the equator of the tire in the tread contact area in the load position of the specified load under the specified internal pressure. A radial tire for a passenger car, characterized in that it has a ground contact rectangular ratio of l/L in the range of 0.85 to 0.95.