JPH0523203B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a pneumatic radial tire, particularly for heavy-load tires, which simultaneously suppresses uneven wear on both sides of the tread edges that occurs on high-speed roads and the wandering phenomenon that occurs on rutted roads. This relates to pneumatic tires. [Prior Art] Generally, heavy-duty radial tires used for trucks, buses, etc., have a reinforcing belt made of at least two layers of metal cords arranged around the outer periphery of the tread portion of at least one layer of the carcass provided in the radial direction. This increases the rigidity of the tread portion. Further, the tread pattern of the tread surface is often a rib pattern in which a plurality of main grooves are provided in the circumferential direction of the tire. In such a radial tire, if the tread surface is shaped to increase the difference in rotation radius between the center and both edges, the lateral force applied to both ends of the tread contact surface can be alleviated.
This has the advantage of improving maneuverability especially when turning. However, on the other hand, when the difference between the two rotation radii is large, there is a problem in that the entire shoulder rib is subjected to shoulder drop friction due to sliding friction, which is called uneven wear. Therefore, as a measure to suppress such shoulder drop wear, it is sufficient to reduce the difference between the two rotation radii described above. However, when doing this, the ground pressure at both edges becomes high, and as a result, a limited area of the edge of the shoulder rib wears out in a step shape due to the action of lateral force that is applied to the tread contact surface when the vehicle turns. , uneven wear called so-called step wear occurs. What's worse, when a radial tire with such a small difference in turning radius on both sides of the tread surface is driven on a rutted road surface, it receives excessive external force from the road surface when escaping from the ruts, causing the steering wheel to deteriorate. This causes a so-called wandering phenomenon, which causes unstable steering. The camber thrust greatly contributes to the above-mentioned wandering phenomenon. Therefore,
As a countermeasure against this wandering phenomenon, as shown in Fig. 4, the camber thrust CT of the tire T is
It is known that it is effective to increase the ground camber angle in the direction of the road surface camber angle φ (positive direction). Conventionally, as a countermeasure against this wandering phenomenon, a method has been proposed in which the shoulder edge of the tread surface is made into a round shoulder with an arcuate shape, thereby increasing the camber thrust CT on the rut-crossing side. ing. However, when such a round shoulder is used, the shoulder edge (tread contact edge) causes a large relative slip with respect to the tread center area, which causes an undesirable problem of significant shoulder drop wear. Ta. That is, in conventional tires, measures against wandering and measures against uneven wear of the tread contact edge have been in a contradictory relationship. [Object of the Invention] The object of the present invention is to solve the various conventional problems mentioned above, to suppress uneven wear that occurs on both edges of the tread contact surface, and to simultaneously suppress the wandering phenomenon that occurs when driving on a rutted road surface. Our goal is to provide pneumatic tires that can [Structure of the Invention] The present invention, which achieves the above object, has a reinforcing belt consisting of at least one layer of a carcass in the radical direction and at least two layers of metal cords provided annularly around the outer periphery of the tread portion of the carcass. In a radial tire in which a rib pattern consisting of a plurality of main grooves extending in the circumferential direction of the tire is formed on the surface of the radial tire, the tread surface is formed not only on the main contact area with a large radius of curvature, but also on the outer edge of a shoulder rib located on the shoulder of the main contact area. An auxiliary ground contact area is formed by an arc that intersects the contour of the main ground contact area with a radius of curvature smaller than the radius of curvature, and has a rotation radius Rc from the tire rotation axis to the center of the tread surface.
and the rotation radius Rs to the edge of the main ground contact area (Rc - Rs) is formed within 2.0% of the rotation radius Rc, and further, the main groove is formed near the edge of the main ground contact area of the shoulder rib. Auxiliary grooves that are thinner than the width and 1.0 to 3.0% of the width TW of the main contact area are provided continuously in the tire circumferential direction, and the main contact area of the divided ribs of the shoulder ribs that are divided from the auxiliary grooves to the shoulder end side Make the width of the area equivalent part more than the width of the auxiliary groove, and make it 1.0 of the width TW of the main ground contact area.
~4.0%, and the width of the shoulder rib divided toward the center of the tread from the auxiliary groove is equal to or greater than the width of the other remaining ribs. 1 to 3 illustrate a heavy-duty radial tire according to an embodiment of the present invention, in which 1 is a tread portion, 2 is a reinforcing belt disposed annularly in the circumferential direction of this tread portion, and 3 is a radial tire for heavy loads according to an embodiment of the present invention. It's a carcass. The carcass 3 is made of organic fiber cords such as nylon, polyester, or polyaramid, or metal cords such as steel, and is arranged in the radial direction. Further, the reinforcing belt 2 is made of metal cord, and has four layers in this embodiment, but at least two layers.
More than one layer is provided. The metal cords constituting the reinforcing belt 2 are inclined at an angle of 10° to 30° in the tire circumferential direction, and each adjacent belt is inclined in opposite directions across the tire circumferential direction. A plurality of (four in this embodiment) main grooves 5, . . . , 5 are provided in the tread surface of the tread portion 1 in the tire circumferential direction. These main grooves provide widths of Ws and Ws′ to both shoulder parts, respectively.
Wide shoulder ribs 4, 4 are formed, and ribs 6, 6, 6, which are narrower than the shoulder ribs 4 having widths Wa, Wb, and Wc, are formed in the central portion. In addition, the wide shoulder rib 4 has
An auxiliary groove 7 extending in the circumferential direction of the tire is provided near the edge thereof, and the tread is divided into a dividing rib 4a on the center side and an outer dividing rib 4b by the auxiliary groove 7. In the present invention, in the above-described tread configuration, the tread surface (tread surface) needs to have a main ground contact area M and also have an auxiliary ground contact area S formed at the outer edge of the shoulder rib 4. The main ground contact area M has multiple radii of curvature TRc,
It consists of a combination of curved surfaces of TRs,
Further, the auxiliary ground contact area S is composed of a curved surface with a radius of curvature Ra, and the contours of the curved surfaces of the main ground contact area M and the auxiliary ground contact area S intersect with each other to form a clear edge-shaped boundary section. is necessary. The main contact area M is mainly a contact surface when driving straight, and the auxiliary contact area S effectively acts as a contact surface when turning and going over ruts.
By forming a clear edge-like boundary between these contact areas M and S as described above, it is possible to eliminate relative slippage in the shoulder area with respect to the central area, thereby preventing shoulder drop wear. It becomes possible to suppress the occurrence. Radius of curvature Ra forming the contour of the auxiliary ground contact area S
It is preferable that the depth is greater than the depth of the main groove and within 5 times the depth of the main groove. More preferably, the center c of the radius of curvature Ra is located on the inner diameter side of the tire from an imaginary line e'-e'' passing through the bottom of the main groove and parallel to the tread surface of the main contact area M. This is because when the radius of curvature Ra and the position of its center C satisfy these requirements, it becomes possible to ensure good ground contact when the vehicle turns. - Minimize the difference (Rc - Rs) between the rotation radius Rc from Z to the center of the tread surface and the rotation radius Rc from the tire rotation axis Z-Z to the edge of the main contact area M as much as possible, and calculate the difference as described above. It is designed to be within 2% of the turning radius Rc. By setting the difference between the two turning radii to be small in this way, the relative slippage of the shoulder area to the tread center area when the tire rotates on the ground is minimized. It is possible to suppress shoulder drop wear in the shoulder area. However, on the other hand, simply reducing the difference between the two turning radii (Rc - Rs) as described above will reduce the ground contact pressure at both edges of the contact surface. becomes higher, and as a result, when the vehicle turns, the lateral force acting on the edge of the main ground contact area on the opposite side to the turning direction increases, making it easier for step wear to occur in a limited area of the shoulder rib edge. When driving on a rutted road surface, the resistance when going over the ruts becomes large, and the camber thrust acts in a negative direction (the opposite direction to the direction in which the tire tries to go over the ruts), causing a wandering phenomenon. In the present invention, the difference between both rotation radii (Rc−Rs) is expressed as Rc
As a countermeasure to eliminate the above-mentioned drawbacks, while taking advantage of the advantage of reducing the shoulder rib to within 2% of the shoulder rib and thereby eliminating the shoulder drop wear of the entire shoulder rib, we have added an auxiliary material that is continuous in the circumferential direction of the tire near the edge of the shoulder rib. The feature is that a groove is provided. By dividing the vicinity of the edge of the shoulder rib into two divided ribs by means of auxiliary grooves that continue in the circumferential direction of the tire, the rigidity of the edge of the shoulder rib can be reduced, and in addition, the edge of the shoulder rib can be Since the arc-shaped auxiliary ground contact area is formed, the camber thrust when passing over ruts can be turned in a positive direction, making it possible to suppress the wandering phenomenon. Further, since the buffer band is formed at the edge of the shoulder rib in this way, it is possible to alleviate the large lateral force applied when the vehicle turns, and to suppress rapid wear of the edge of the rib. In the present invention, in order to reliably obtain the above-mentioned effects, it is not enough to simply provide an auxiliary groove in the area near the edge of the shoulder rib, but also to make the following dimensional settings. That's true. That is, the width g of the auxiliary groove 7 is the width G of the main groove 5.
It should be smaller than that and within the range of 1.0 to 3.0% of the width TW of the main contact area M of the tread surface. Moreover, among the divided ribs 4a and 4b formed by dividing the shoulder rib 4 by this auxiliary groove 7, the width Wr of the portion corresponding to the main ground contact area of the divided rib 4b located on the outside
is equal to or greater than the width g of the auxiliary groove 7, and is in the range of 1.0 to 4.0% of the width TW of the main ground contact area M. In this way, the outer divided rib 4b, as a part of the main ground contact area M having a common outline with the inner divided rib 4a, has a width equal to or greater than the width g of the auxiliary groove 7, and is 1.0 of the width TW of the main ground contact area M. By having a width Wr of ~4.0%, step wear of the shoulder rib can be eliminated. This step wear occurs when the width Wr of the split rib 4b is too small, the split rib 4a side wears out faster than the split rib 4b, and conversely the width
If Wr is too large, the dividing rib 4b side will wear out faster than the dividing rib 4a. Furthermore, the split rib 4b having the above-mentioned width Wr prevents the gradual wear of the shoulder rib edge caused by a relatively small lateral force (such as pliesteer) generated by the tire itself during straight running. will also exert an effective deterrent effect. Furthermore, it can also serve to protect the edges of the divided ribs 4a inside the auxiliary groove 7 against lateral forces that are applied to the tread contact surface during sudden turns. It is preferable that the groove depth dn of the above-mentioned auxiliary groove is 90% or more of the groove depth dm of the main groove adjacent to the auxiliary groove. By setting such a groove depth dn, the auxiliary groove can be made to exist until near the end of wear of the main groove, so that the above-described effects of the present invention can be exhibited throughout the life of the tire. I can do it. Furthermore, in the present invention, the width Wt of the dividing rib 4a near the center of the tread is set to be equal to or greater than the width of the other remaining ribs 6. In this case, when the widths Wa, Wb, and Wc of the plurality of ribs 6 near the center of the tread are different, they are set to be equal to or greater than the maximum width. Note that the rib width and groove width mentioned above refer to the rib width (Wt,
Wa, Wb, Wc, etc.) and groove width (G, g, etc.). By setting the rib width as described above,
The rigidity of the split rib 4a is increased by adjusting the rigidity of the rib 6 closer to the center of the tread.
The rigidity can be made equal to or higher than that of Combined with the effect of acting on the above, it becomes possible to suppress the wandering phenomenon. The upper limit of the width Wt of the divided ribs 4a is preferably within 1.4 times the widths Wa, Wb, and Wc of the ribs 6 closer to the center. [Example] Example 1 Four types of tires A, B, C, and D, which all have the following common structure except for mutual differences as described in the section of tires A, B, C, and D below. was produced. Tire size: 1000R20 14PR Tire structure: Structure shown in Figures 1 to 3 Carcass: Steel cord layer, 1 layer Reinforcement belt: Steel cord layer, 4 layers Width of main contact area: 204mm Rib width of center and second ribs: Wa=Wb=Wc=28mm Rib width of shoulder rib: Wt=Wt′=32mm Radius of curvature of center area of main contact area: TRc=540mm Radius of curvature of shoulder area of main contact area: TRc=480mm Rotation around tread width center Radius: Rc = 525.5mm Rotation radius of main contact area edge: Rs = 515.5mm Tire A: No auxiliary groove corresponding to the present invention is provided near the edge of the shoulder rib, and the contour is continuous with respect to the edge of the shoulder rib. Tire with a round shoulder connected tangentially to the main ground contact area Tire B: The vicinity of the edge of the shoulder rib is divided by an auxiliary groove (groove width 3.0 mm) corresponding to the present invention, and the outside of the divided side The width Wr of the part corresponding to the main ground contact area of the dividing rib is 1.5 mm (main ground contact area width TW
Tire C: The vicinity of the edge of the shoulder rib is divided by an auxiliary groove (groove width 3.0 mm) corresponding to the present invention, And the width Wr of the part corresponding to the main ground contact area of the divided outer divided rib is 10.0 mm (main ground contact area width TW
), and the radius of curvature Ra = 25mm.
Tire that formed an auxiliary ground contact area Tire D: The vicinity of the edge of the shoulder rib is divided by an auxiliary groove (groove width 3.0 mm) corresponding to the present invention, and the area corresponding to the main ground contact area of the divided outer divided rib The width Wr of the part is 5.0mm (main contact area width TW)
2.4%) and formed an auxiliary ground contact area with a radius of curvature Ra = 25 mm Among the above tires, Tire D is the tire of the present invention, and Tires A, B, and C are comparative tires. Air pressure of each tire 7.25Kg/cm ² , rim 7.50V
×20 was attached to the steering wheel, and the wear of the shoulder rib was evaluated after driving 25,000 km through an actual vehicle test with a load of 2,500 kg. As a result, the wear status of the shoulder ribs of each tire is as shown in Fig. 5. Tire A is shown in Fig. 5A, Tire B is shown in Fig. 5B, Tire C is shown in Fig. 5C,
Tire D was worn as shown in Figure 5D. (In each figure, the part indicated by the broken line shows the shape before wear.) That is, as shown in FIG. 5A, tire A had significant shoulder-drop wear at the shoulder rib edge. In tire B, as shown in FIG. 5B, the outer dividing rib 4b was left unused due to wear, and only the inner dividing rib 4a had progressed to wear. As shown in FIG. 5C, the tire C was so worn that the outer dividing rib 4b preceded the inner dividing rib 4a by a certain amount. Furthermore, as shown in FIG. 5D, tire D, which is a tire of the present invention, wore both the divided ribs 4a and 4b on average, and the amount of wear was smaller overall than the comparative tire. Example 2 Each tire has a one-layer carcass made of metal cords with the same internal structure and four layers of reinforcing belts made of metal cords, and has the same tire size.
1000R20 14PR, and the tread pattern is a 5-rib pattern with four main grooves as shown in Figures 1 to 3, and the width of the main contact area is
It has a tread pattern with a TW of 204mm, and the width of the divided ribs near the center of the shoulder ribs is the same on the left and right sides (Wt = Wt'), and the widths of the three central ribs are all the same (Wa = Wb = Wc), and Wt (=Wt′) and Wa
(=Wb=Wc), tires E, F, G, and H were manufactured with different values as shown below. In addition, the groove width g of the auxiliary groove at this time is 3.0 mm, and the width of the dividing rib
The common Wr was 5.0mm. Furthermore, a tire similar to the above tire G without the auxiliary groove was manufactured as Tire I.

〔Effect of the invention〕

As mentioned above, the pneumatic radial tire of the present invention is based on a tread structure in which the difference in the rotation radius between the center of the tread surface and the edge is smaller than that of conventional tires, and the shoulder ribs are continuous in the tire circumferential direction near the edge. In addition to providing auxiliary grooves to reduce curvature, we also skillfully combined the auxiliary ground contact area consisting of a contour with a small radius of curvature, thereby achieving the effect of suppressing uneven wear of the tread portion and the effect of suppressing wandering, which have conventionally been considered contradictory characteristics. so that they can be achieved at the same time. In addition, as mentioned above, among the shoulder ribs divided by the auxiliary grooves, by adopting a structure that ensures the rigidity of the inner divided ribs, the difference between the two rotation radii of the tread surface is made smaller than before. It is possible to sufficiently compensate for the decrease in maneuverability during turning.

[Brief explanation of drawings]

FIG. 1 is a half-sectional view of a radial tire according to an embodiment of the present invention, FIG. 2 is an enlarged half-sectional view of the same portion, and FIG. 3 is a plan view of the tread portion of the radial tire.
Fig. 4 is an explanatory diagram explaining the wandering phenomenon, Figs. 5 A to D are sectional views showing the wear status of the shoulder ribs of the conventional tire and the tire of the present invention, respectively, and Fig. 6 is the rib of the conventional tire and the tire of the present invention. Width ratio
FIG. 7 is a diagram showing the relationship between Wt/Wa and cornering power CP, and FIG. 7 is a diagram showing the relationship between the camber angle and camber thrust of a conventional tire and a tire of the present invention. 1...Tread section, 2...Reinforcement belt, 3...
Carcass, 4...Shoulder ribs, 4a, 4b...
...Divided rib, 5...Main groove, 6...Rib (near the center of the tread), 7...Auxiliary groove, M...Main ground contact area, S...Auxiliary ground contact area.

Claims (1)

[Scope of Claims] 1. A reinforcing belt consisting of at least one layer of radial carcass and at least two layers of metal cords provided annularly around the outer periphery of the tread portion of the carcass. In a pneumatic radial tire with a rib pattern formed of a plurality of extending main grooves, the tread surface is attached to a main contact area with a large radius of curvature, as well as to an outer edge of a shoulder rib located on a shoulder of the main contact area with a radius of curvature larger than the radius of curvature. Also forms an auxiliary ground contact area consisting of a circular arc that intersects the outline of the main ground contact area with a small radius of curvature, and has a rotation radius Rc from the tire rotation axis to the center of the tread surface.
and the rotation radius Rs to the edge of the main ground contact area (Rc - Rs) is formed within 2.0% of the rotation radius Rc, and further, the main groove is formed near the edge of the main ground contact area of the shoulder rib. Auxiliary grooves that are thinner than the width and 1.0 to 3.0% of the width TW of the main contact area are provided continuously in the tire circumferential direction, and the main contact area of the divided ribs of the shoulder ribs that are divided from the auxiliary grooves to the shoulder end side Make the width of the area equivalent part more than the width of the auxiliary groove, and make it 1.0 to 1.0 of the width TW of the main ground contact area.
4.0%, and the width of the shoulder rib divided toward the center of the tread from the auxiliary groove is equal to or greater than the width of the remaining ribs.