JPS63134314A - Pnermatic radial tire - Google Patents

Abstract

PURPOSE:To suppress the eccentric abrasion of a tread part by setting the difference of revolution radius between at the center of the tread part and the edge part small and specifying the difference between the main grounded region and the width between the crossing points of the supposed line on the bottom part of the main groove with the both tread side surfaces and forming radial kerves in the auxiliary grounded region. CONSTITUTION:A tread part 1 consists of a main grounded region M having the large radii TRc and TRs of curvature and an auxiliary grounded region S which has the radius Ra of curvature which is larger than the depth dm of a main groove 5 and smaller than two times. The difference between the revolution radius Rc ranging from the tire revolution axis to the center of the tread surface and the revolution radius Rs to the edge part M of the main grounded region is set within 2.0% of the revolution radius Rc. Further, the difference between the width TW of the main grounded region M and the width RW between the both crossing points Q and Q where the supported line e-e passing in parallel through the tread surface in the main grounded region M on the bottom part of the main groove 5 cross with the both side surfaces of the shoulder part is set to 1.0-2.0 of the depth dm of the main groove 5. Further, kerves 7 are formed in the radial direction on the auxiliary grounded region S.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a pneumatic radial tire, and particularly in the case of a heavy-load tire, uneven wear of both edges of the tread surface that occurs on high-speed roads, and wandering that occurs on rutted road surfaces. This invention relates to a pneumatic tire that simultaneously suppresses these phenomena.

[Prior art]

Generally, radial tires for heavy loads used in trunks, buses, etc. are constructed by arranging a reinforcing belt made of at least two layers of metal cords around the outer periphery of the tread of a carcass provided in at least one layer in the radial direction. We are trying to increase the rigidity of the 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 turning radius between the center and both edges, it is possible to alleviate the lateral force applied to both ends of the tread contact area, especially when turning. This has the advantage of improving maneuverability. However, on the other hand, when the difference in the re-rotation radius is large, there is a problem in that the entire shoulder rib is worn down 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 above-mentioned difference in the re-rotation radius. However, when doing this, the ground contact 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-like manner due to the action of lateral force applied to the tread contact surface when the vehicle turns. Uneven wear, so-called step wear, begins to occur.

What's even worse is that when radial tires, which have a small difference in turning radius on both sides of the tread surface, drive on a rutted road surface, they receive 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 contributes to the wandering phenomenon described above. Therefore, as a countermeasure against this wandering phenomenon, it is effective to increase the camber thrust CT of the tire T in the direction of the road surface camber angle φ (positive direction) as shown in Fig. 5. It is known that

Conventionally, as a countermeasure against this wandering phenomenon, the shoulder of the tread portion is formed into a tapered shoulder cut diagonally, and a radial kerf is provided on the tapered shoulder, as disclosed in Japanese Unexamined Patent Publication No. 54-15504. Something like this has been proposed. However, with this tread structure, in order to sufficiently reduce rut crossing resistance, it is necessary to make the tapered shoulder portion considerably wider, which narrows the actual tread width and increases the resistance required for tire performance. There is a problem that abrasion resistance is reduced.

Furthermore, in Japanese Patent Application Laid-Open No. 60-60009, it is proposed that the shoulder be replaced with the above-mentioned Taber shoulder by an arcuate round shoulder, and that the round shoulder be provided with a radial cuff that extends to the deformed part of the ground contact end. ing.

However, in this case as well, the area where the radial calf is arranged increases, which narrows the actual tread width in the same way as above, and reduces the stiffness of the shoulder area, which reduces wear resistance and maneuverability when turning. I have a problem.

[Purpose of the invention]

The purpose of the present invention is to solve the various conventional problems mentioned above, and simultaneously suppress uneven wear occurring at both edges of the tread contact surface and suppress the rut wandering phenomenon, without reducing wear resistance or maneuverability. The objective is to provide a pneumatic tire that can achieve this goal.

[Structure of the invention]

To achieve the above object, the present invention has 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. 2. A radial tire having a pattern formed with a plurality of main grooves extending in the tread surface, in addition to the main ground contact area having a large radius of curvature, the outer edge of the shoulder part has a groove depth greater than that of the main groove;
forming an auxiliary ground contact area consisting of an arc that intersects the outline of the main ground contact area with a radius of curvature smaller than 0 times, and a rotation radius R from the tire rotation axis to the center of the tread surface;
c and the rotation radius Rs to the edge of the main ground contact area (R
e-Rs) is formed within 2°0% of the rotation radius Rc, and a groove bottom imaginary line passing through the groove bottom of the main groove parallel to the tread surface of the main ground contact area intersects both side surfaces of the shoulder part. The difference between the width RW between both intersections and the width TW of the main ground contact area (RW
-TW) is 1.0 to 2.0 times the groove depth of the main groove; It is characterized by having the following.

1 to 4 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 arranged in an annular manner in the circumferential direction of the tread portion, and 3 is a reinforcing belt disposed in a ring shape around the tread portion; It's a carcass. The carcass 3 is made of an organic fiber cord such as nylon, polyester, or polyaramid, or a metal cord such as steel, and is arranged in the radial direction. Further, the reinforcing belt 2 is made of a metal cord, and has four layers in this embodiment, but at least two layers are provided.

The metal cords constituting the reinforcing belt 2 are inclined at an angle of 10° to 306° in the tire circumferential direction, and are arranged in opposite directions between adjacent belts in the tire circumferential direction.

A plurality of (four in this embodiment) main grooves 5, -15 are provided in the tire circumferential direction on the ground contact surface (tread surface) of the tread portion 1. These main grooves form slightly wide shoulder ribs 4, 4 with widths Ws and Ws', respectively, in both shoulder parts, and widths Wa, Wb, and 4 in the central part.
A rib 6.6.6 is formed which is slightly narrower than the shoulder rib 4 of 1ilc. Furthermore, a large number of radial cuffs 7, -17 are provided at predetermined pinches on the outer edges of the shoulder ribs 4.degree. 4 on both sides, respectively.

In the present invention, in the above-described tread configuration, it is necessary that the tread surface (tread surface) has a main ground contact area M and also has an auxiliary ground contact area S formed at the outer edge of the shoulder rib 4. . In such a configuration, the difference between the rotation radius Re from the tire rotation axis Z-Z to the center of the tread surface and the rotation radius Rs from the tire rotation axis Z-Z to the edge of the main contact area M (Rc-Rs ) must be made as small as possible, and even if the difference is large, it should be limited to 2% of the radius of rotation Rc. By reducing the difference in the re-rotation radius in this way, it becomes possible to suppress shoulder drop wear in the shoulder area. In other words, this re-rotation radius difference (Rc - Rs) is the rotation radius Rc
If it is made larger than 2%, it will cause relative sliding friction such that the shoulder area becomes larger than the center area.
Since shoulder drop wear of the entire shoulder rib occurs significantly, the object of the present invention cannot be achieved.

Furthermore, in the present invention, the main ground contact area M is composed of a combination of curved surfaces with a plurality of radii of curvature TRc and TRs, and the auxiliary ground contact area S is composed of a curved surface with a radius of curvature Ra, and the contours of these side curved surfaces intersect with each other. It is necessary to form a clear edge-like boundary division. 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 overcoming ruts. By forming a clear edge-like boundary division, it is possible to eliminate relative slippage in the shoulder region with respect to the central region, and to suppress the occurrence of over-the-counter wear.

However, as mentioned above, it is simply the difference in rerotation radius (Re−R
If s) is only made smaller, as mentioned above, the ground contact pressure on both edges of the ground contact surface will increase, 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 will increase. Step wear begins to occur in a limited area on the edge of the shoulder rib, and when driving on rutted roads, the tire's camphor thrust acts in the negative direction, which increases the resistance when going over ruts, causing the wandering phenomenon. will occur.

In the present invention, the difference in the rerotation radius (Rc - Rs) is calculated as
As a measure to eliminate the above-mentioned drawbacks, the radius of curvature that forms the auxiliary ground contact area S has been reduced while taking advantage of the feature of eliminating shoulder drop wear of the entire shoulder rib, which can be obtained by reducing c to within 2%. The auxiliary ground contact area S is set to a predetermined size, and a radial calf is provided at a predetermined depth.

With this configuration, the stiffness of the shoulder rib edge is reduced and the direction of the camber thrust when passing over ruts is changed to a positive direction, so that the wandering phenomenon can be suppressed. Furthermore, since a buffer band is formed at the edge of the shoulder rib in this manner, the large lateral force applied when the vehicle turns is alleviated, and rapid wear of the edge of the rib is suppressed.

In the present invention, in order to ensure the above effects, the radius of curvature Ra forming the outline of the auxiliary ground contact area S is larger than the groove depth dm of the main groove, and It is necessary to make sure that it is within 2 times. By setting such a radius of curvature, the camper thrust CT can be set in a positive direction without causing a significant decrease in maneuverability during turning (cornering power CP), as will be clear from the examples described later. This makes it possible to exhibit a good effect of suppressing the wandering phenomenon.

In providing the auxiliary ground contact area S with such a radius of curvature Ra, it is more preferable that the center C of the radius of curvature Ra is
It is preferable that the groove be located on the inner diameter side of the tire from the groove bottom imaginary line e' - e'' which is along the groove bottom of the main groove and parallel to the tread surface of the main ground contact area M.By satisfying such requirements, the vehicle turning This makes it possible to improve ground contact when driving, and further improve steering stability.

Further, in the present invention, the radial cuffs 7 provided in the left and right auxiliary ground contact regions S need to have a maximum depth dc in the range of 4 to 7 mm when measured from the surface of the auxiliary ground contact regions S. Further, if necessary, the cut of this radial calf may be made to extend to the main ground contact area M side, but the length ω thereof is 0 to 2% of the width TW of the main ground contact area M.
It should be stopped within the next few days.

In the present invention, the thickness of the radial cuff provided as described above (the width of the cut groove) is preferably 0°3 to 1.0 mm, and the pitch between these kerfs is preferably 0.3 to 1.0 mm.
It is preferable that the width TW is in the range of 1 to 7% of the width TW. Further, the depth of the kerf in the radial direction is preferably 90% or more and less than 100% of the groove depth of the main groove adjacent to the kerf. By setting the depth to such a depth, the above-mentioned effect of the kerf can be exhibited until the end of wear of the main groove.

Furthermore, what is important in the present invention is that the groove bottom virtual line e
An intersection Q where '-e' intersects both sides of the tread part,
The difference between the width RW between Q and the width TW of the main grounding area M (RW-
TW) to be in the range of 1.0 to 2.0 times the leading groove depth dm.

If the above difference (RW-TW) is so large as to exceed 2.0 times the main groove depth dm, the wear resistance will decrease due to a decrease in the width of the main contact area of the tread (tread development width) and a decrease in the rigidity of the shoulder ribs. The decrease becomes noticeable and reduces the life of the tire. Furthermore, if the above difference (RΔ-TW) is smaller than 1.0 times the main groove depth dm, the auxiliary grounding area S
Therefore, the effect of the radial cuff cannot be fully exhibited, and the effect of suppressing the rutting and wandering phenomenon according to the present invention cannot be obtained.

Furthermore, in the present invention, the widths Wt and Wt' of the main ground contact area portion of the shoulder rib 4 excluding the cut portion ω of the radial calf are the widths Ha and Wb of the other ribs 6 near the center of the tread. , Wc is preferably larger. By setting such a rib width, the stiffness of the shoulder rib can be made equal to or higher than the stiffness of the rib 6 near the center of the tread, thereby suppressing a decrease in cornering power. In other words, if cornering power decreases,
Even if the camber thrust is positive, the straight-line stability and maneuverability on rutted roads deteriorate, and the wandering phenomenon is not sufficiently suppressed. In the present invention, the wandering phenomenon can be effectively suppressed by having the camber thrust in the positive direction and increasing the cornering power as described above.

In addition, in the present invention, the above-mentioned rib width is defined as the rib width (Wt, Wa, Wb, W) by the average value of the maximum width and minimum width, as shown in FIG.
(c, etc.).

Further, in the above-mentioned embodiment, the case where the tread pattern is a rib pattern has been explained, but in the present invention, even if the tread pattern is a block pattern, the block rows of the shoulder portion are arranged substantially in the circumferential direction of the tire like ribs. It is included as long as it has a ribbed tone, and similar effects can be expected.

〔Example〕

Example 1 Each tire basically has a 5-rib pattern with 4 main grooves as shown in Figures 1 to 4, except for the following differences, and the groove bottom of the main groove. The intersection point Q between the virtual line and both sides of the tread, and the width between Q is 1? W is 222mm,
It has a tread pattern with a main groove depth dm of 14 mm, and is made of metal cords with the same specifications as the internal structure.
It has a four-layer reinforcing belt consisting of a carcass layer and a metal cord, and the rotation radius of the tread surface Rc = 525 mm, R
s = 518mm, and the difference (Rc - Rs) is R
1.3% of c, same tire size 1000R20
6 types consisting of! (7) Tires A, B, and C.

I made D, E, and F.

Tire A: Square shoulder (width of main contact area TW - 218mm
Tire B: Tire with conventional structure (without auxiliary contact area and radial cuff) Tire B: Tire with auxiliary contact area and radial kerf under the following conditions in parentheses (radius of curvature of auxiliary contact area Ra = 10 mm, main contact area Intersect at width Th = 202 mm; maximum cutting depth of radial kerf dC = 5 mm.

Cut width to the main contact area side ω = 2mm, pinch + = 8
mm) Tire C: In Tire B, only the ground contact area conditions are different as shown in the following parenthesized conditions (the radius of curvature of the auxiliary ground contact area Ra = 15 mm and the width of the main ground contact area intersects at -202 mm) Tire D Near Tire B Tire E: Tire B has different ground contact area conditions as shown in parentheses below (the radius of curvature of the auxiliary contact area Ra = 20 mm and the width of the main contact area T - 202 mm). Tires with different conditions only as shown in the following parentheses (the radius of curvature of the auxiliary contact area Ra = 25 mm and the width of the main contact area TW - 202 mm intersect) Tire F: For tire B, only the conditions of the contact area are in the following parentheses. Among the above tires, tires C, D, and E are tires of the present invention; ,
F is a comparison tire.

For each tire, air pressure 7.25 kg/, f
Under the measurement conditions of fl, IJ 7.50VX20, and load 2700kg, cornering power CP (kg/deg) is a representative value of maneuverability, and camber thrust stiffness CT- is a representative value of wandering performance.
S (kg/deg) (the inclination of the camber thrust at a gamber angle of 0 to 2 degrees) was measured.

The results were as shown in Table 1.

Table 1 From the results in Table 1, it can be seen that tires C, D, and E in which the radius of curvature Ra of the auxiliary ground contact area is larger than the main groove depth dm (= 14 mm) and smaller than 2.0 times have a camber The thrust stiffness CT-3 turned positive (+), indicating that there was an effect of suppressing the wandering phenomenon.

However, in tire F where the radius of curvature Ra is set to be more than 2.0 times the main groove depth ctm, the cornering power CP tends to be lower than that of tire A with a square shoulder shape, resulting in a decrease in maneuverability. It showed that.

Example 2 The cut configuration of the radial calf is the same as that of tire B- in Example 1.
F, etc., and for the case where the radius of curvature Ra of the auxiliary ground contact area is set constant at 15 mm and the case where it is set constant at 25 mm, the width RW between the intersection Q of the virtual groove bottom line and Q = 222 mm ( (constant), the width TW of the main ground contact area was set to 212 mm, 208 mm, respectively.
Tires G, H, and I changed to 202mm, 198mm, and 192mm.

K, L, M, N, and ○ were produced.

Among these tires, tires G, H, I, and L.

M and N are tires of the present invention, and tires J and K.

0 is a comparison tire. Tire A in Example 1 is also shown for comparison.

For these tires, the same cornering power CP1 and camper thrust stiffness CT-3 as in Example 1 were measured.
The wear resistance WS of the tread surface was measured after 11 runs. The results are shown in Table 2 (when Ra = 15 mm) and Table 3.
The results were as shown in the table (when Ra=25 mm).

The wear resistance WS in the table is obtained by measuring the remaining amount of the main groove, and is expressed as an index with Tire A (square shoulder tire) in Example 1 set as 100.

Table 2 (when Ra = 15mm) Table 3 (when Ra = 25mm) From Tables 2 and 3 above, the width RW between the intersections Q and Q.
A tire in which the difference (RW-TW) between the main groove depth dm and the width TW of the main ground contact area is equal to (1.0 times) or more the main groove depth dm = 1.4 mm has a camber thrust regardless of the radius of curvature Ra. It can be seen that the stiffness CT-3 has turned to the plus (+) side, showing a good effect of suppressing the wandering phenomenon.

However, as the difference (RW - TW) increases, the actual tread width decreases and the stiffness of the shoulder ribs decreases, so the wear resistance decreases, especially when the difference (RW - TW) increases.
) is more than 2.0 times the main groove depth dm, it can be seen that the wear resistance of Tire 0 is significantly reduced.

Example 3 In addition to the comparative tire A (square shoulder tire) and the tire E of the present invention in Example 1, the following comparative tires P, Q, R, and S were also manufactured.

Tire P: Tires that differ in the following parenthetical conditions at the tire width (the auxiliary ground contact area must be a round shoulder with a radius of curvature of 25 mm and its outline is tangentially connected to the main ground contact area; the maximum cutting depth of the radial kerf dc =5
1) Tire Q: Tire P with dc=8mm Tire R: Tire E with the following parenthetical conditions different (TW-202mm, tapered at an angle of 45° in the radial direction, radial Tire S: Tire R, TW = 194 mm, radial length of the tapered shoulder - 14 mm.

For these tires, the maximum depth of the radial kerf was changed to 18 mm. Similarly to Example 2, the cornering power CP, which is a representative value of maneuverability, and the camber thrust stiffness CT-, which is a representative value of wandering performance, were determined.
The wear resistance was measured after running 30,000 km, 20,000 km, and 50,000 km, and the state of uneven wear was also observed. The result is
It was as shown in Table 4.

(Margins below this page) Table 4 (note) 1)...Step wear 2)...Shoulder drop wear 3)...Shoulder drop wear From Table 4, it can be seen that the comparison tire S has a too deep kerf. Since the stiffness of the shoulder ribs was reduced, the cornering power CP was significantly lower than that of tire A with square shoulders, and a decrease in maneuverability was observed. Comparison tire R
The camber thrust stiffness CT-3 was negative (-), and a wandering phenomenon occurred.

Furthermore, the wear resistance was significantly lower than that of Tire A due to the reduction in the actual tread width.

Tire Q also had significantly reduced wear resistance due to a decrease in the actual tread width, and also suffered from shoulder drop wear on the entire shoulder rib. Furthermore, the tire P had significant shoulder drop wear over the entire shoulder rib.

In contrast, the tire E of the present invention has a cornering power C
The decrease in P is not so large compared to tire A, and the camber thrust stiffness CT-3 is also positive (+), indicating a good wandering phenomenon suppression effect.
Furthermore, the wear resistance was comparable to that of Tire A, and uneven wear such as step wear and shoulder drop wear did not occur at all.

〔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 rotational radius between the center of the tread surface and the edge is smaller than that of conventional tires, and a specific radius of curvature at the shoulder edge. The auxiliary ground contact area is provided so as to intersect with the outline of the main ground contact area, and furthermore, the difference between the width between the intersections of the groove bottom virtual line of the main groove with both tread sides and the main ground contact area is within a specific range, and the above-mentioned By providing a radial calf with a certain depth in the auxiliary ground contact area, it has the effect of suppressing uneven wear that occurs on both edges of the tread contact surface and suppressing the rut wandering phenomenon without reducing wear resistance or maneuverability. can be achieved at the same time.

[Brief explanation of the drawing]

FIG. 1 is a half-sectional view of a radial tire according to an embodiment of the present invention, FIGS. 2 and 3 are enlarged sectional views of the same portions, FIG. 4 is a plan view of the tread portion of the radial tire, and FIG. 5 FIG. 2 is an explanatory diagram illustrating the wandering phenomenon. 1... Tread portion, 2... Reinforcement belt, 3...
・Carcass, 4... Shoulder rib, 5... Main groove, 6... Rib (near the center of the tread), 7...
- Calf, M...Main ground contact area, S...Auxiliary ground contact area. Figure 2 Figure 3 Figure 4 Cause

Claims (3)

[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, and a plurality of main grooves extending in the circumferential direction of the tire on the tread surface. 2. In a radial tire formed with a pattern, the tread surface has a groove depth greater than that of the main groove at the outer edge of the shoulder portion, in addition to the main ground contact area having a large radius of curvature;
forming an auxiliary ground contact area consisting of an arc that intersects the outline of the main ground contact area with a radius of curvature smaller than 0 times, and a rotation radius R from the tire rotation axis to the center of the tread surface;
c and the rotation radius Rs to the edge of the main ground contact area (R
c-Rs) is formed within 2.0% of the rotation radius Rc, and a groove bottom imaginary line passing through the groove bottom of the main groove parallel to the tread surface of the main ground contact area intersects both side surfaces of the shoulder part. The difference between the width RW between both intersection points and the width TW of the main ground contact area (RW-
TW) is 1.0 to 2.0 times the groove depth of the main groove, and the auxiliary ground contact area is further provided with a radial direction kerf with a maximum depth of 4 to 7 mm measured from the surface of this auxiliary ground contact area. A pneumatic radial tire characterized by: (2) A patent claim in which the center of the radius of curvature of the circular arc forming the outline of the auxiliary ground contact area is located on the inner diameter side of the tire from a groove bottom imaginary line that passes through the groove bottom of the main groove and is parallel to the tread surface of the main ground contact area. A pneumatic radial tire according to item 1. (3) The cutting depth of the radial direction kerf from the boundary between the main contact area and the auxiliary contact area to the main contact area side is
The pneumatic radial tire according to claim 1 or 2, wherein the width TW of the main ground contact area is within the range of 0 to 2%.