JPS6212041B2 - - Google Patents

Abstract

PURPOSE:To use a tire on good and bad roads further prevent its uneven wear, in the captioned tire having at least five tread main grooves, by changing a sloped angle of groove walls at each main groove of central part, side parts and intermediate parts between these side parts and the central part. CONSTITUTION:In a tire of tread pattern, having at least five circumferentially extended zigzag shaped tread main grooves, a central part circumferential main groove 1, arranged in the central area of a tread Tr, a pair of side part circumferential main grooves 3, partitioning outermost side ribs 6 of the tread Tr, and intermediate part circumferential main groove 2, arranged between these grooves, the main groove 1 is formed to laterally symmetrical cross sectional shape sloped at a prescribed angle. While the main groove 2 is formed to laterally symmetrical cross sectional shape having a folding linear groove wall slope, further the main groove 3 is formed to laterally unsymmetrical cross sectional shape with a sloped angle of an axially outside groove wall larger than that of an axially inside groove wall.

Description

[Detailed description of the invention]

This invention relates to a pneumatic radial tire for heavy loads, and is particularly suitable for high-speed continuous running on good roads for trucks and buses, as well as on rough roads such as general unpaved roads or construction sites. This invention relates to an improvement in the groove shape of the tread of this type of tire used for wrapping purposes. In general, radial tires that use metal cords as belt reinforcements have a stronger belt placed between the tread rubber and carcass ply than ordinary bias tires, so they have many advantages such as wear resistance and puncture resistance. On the other hand, due to the strong reinforcing effect of the belt, there is a problem with ride comfort, so it is not suitable for use on rough roads, but it has been developed especially for use on good roads, and it is suitable for road conditions such as the development of expressway networks. Demand has increased significantly in recent years as a result of significant improvements. In such applications, tire tread determines traction, braking performance, general wear resistance,
In consideration of heat resistance, etc., a circumferential rib is provided that is limited by a plurality of tread main grooves that extend in a zigzag shape in the circumferential direction of the tire.Such a tread pattern is generally called a rib type. The number of rib sections in the tread main groove determines the wet performance of the tire, i.e. the traction when wet.
Various designs are designed taking into account the balance between performance such as braking and skidding resistance, wear resistance, and tread width. However, when the above-mentioned wet performance is emphasized, or when the tread width is wide, the tread main groove is Requires several books. These ribs are usually continuous in the circumferential direction of the tire, but sometimes they are interrupted by horizontal grooves along the width of the tire, making them discontinuous in the circumferential direction, but in any case, under high operating speeds, During continuous driving over long distances, unique uneven wear occurs. In other words, one type is mainly continuous running in a straight line, which starts at the side end of the circumferential rib 5 of the tire T and continues in the circumferential direction, as shown in a partial meridional cross-sectional view of the tire in FIG. , Width W, and uneven wear called railway wear that accelerates over the step δ.Furthermore, it is mainly affected by turning, and Fig. 2 shows a partial external view of the tire as seen from the axial direction. In particular, a step δ' occurs intermittently along the circumferential direction of the tire T starting from the axially outer end of the outermost circumferential rib 6 in the axial direction, and the circumferential rib 6 This is uneven wear called wavy wear where the wear occurs partially. Such uneven wear not only makes the appearance of the tire T extremely unsightly, but also adversely affects various tire performances, particularly traction, braking performance, turning performance, etc., and significantly shortens the life of the tire. Moreover, even if a vehicle is equipped with tires designed for good roads, it is unavoidable that some of its routes include rough roads.For example, trucks, for example, have to drive to construction sites, so they are scattered on the road surface. There are many opportunities for foreign objects such as crushed stones to get caught in the main groove. Heavy-duty pneumatic radial tires have strong tread reinforcement as described above to suppress tread movement in the contact area, so they are susceptible to stone entrapment, and if stone encroachment occurs, the restraint is strong enough to cause the tire to eject. Therefore, each time the tire rotates, the groove bottom of the tread main groove hits the reinforcement of the tread part, that is, the base rubber between it and the belt, causing its destruction.
This can lead to internal damage to the reinforcing structure, and especially when the belt is a metal cord, water can enter from the damaged base rubber, causing rusting, and peeling from the rubber can result in long-term use, including tire replacement. There is a risk of fatal damage over the lifespan. In the past, various attempts have been made to individually solve the two drawbacks mentioned above, namely the occurrence of uneven wear and the problem of stone formation, but all of them have been made by making the cross-sectional shape of all tread main grooves almost the same. Because of the setting, it was not possible to solve these drawbacks at the same time. Or, for example,
As seen in Japanese Patent No. 15282, the cross-sectional shape of the tread main groove adjacent to the central rib is such that the width of the central rib decreases inward in the radial direction of the tire, and the width of the central rib is reduced by a cut from the rib. Some systems have been designed with separate protrusions to adjust the shape of the grooves, thereby reducing railway wear in each tread main groove and at the same time preventing stone build-up, but the grooves have complex shapes and are difficult to manufacture. Moreover, Toledo as a whole does not effectively solve the above problems. Therefore, this invention solves the above-mentioned two problems of uneven wear and stone build-up of this type of tire, which can be used on both good roads and unavoidable use on bad roads. To provide a tire in which circumferential ribs are partitioned by regular tread grooves, and the tread of the tire is effectively resolved over the entire tread. Regarding the tread pattern shown in FIG. 3, which illustrates an example in which circumferential ribs are partitioned by five tread grooves, the inventors have found that (1) each of all the tread main grooves 1, 2, and 3 is When the inclination angle of the groove wall, which forms an acute angle with respect to the normal line of the tread passing through the groove edge, is set relatively large, when driving on a good road, the outer end 4 _-2 of the circumferential rib 4 and both ends of the circumferential rib 5 Railway wear is likely to occur in sections _5-2 and _5-3 . (2) If the above-mentioned groove wall inclination angles of all tread main grooves 1, 2, and 3 are set to a relatively small Wave-like wear is likely to occur on the outer rib 6 starting from the outer end 6 _-0 , and when driving on rough roads, stones are likely to form in the tread main grooves 1, 2, and 3. It was found that the degree of rock formation was greater in the main groove. This tendency was the same when the circumferential ribs were divided by six tread grooves, with one pair of tread main grooves 1. Based on the above facts, we focused on the fact that the positions where uneven wear such as railway wear, wave wear, and stone chips are likely to occur are different in the tread, and changed the groove wall inclination angle for each position of the tread main groove. Thus, it has been found that it is possible to improve the above-mentioned problems and provide a tire that is advantageously suitable for use on both good and bad roads. This invention consists of a carcass consisting of at least one ply in which cords are arranged in the radial surface of the tire (including a plane making a very shallow angle with this surface), and a carcass that surrounds the carcass and extends in the circumferential direction of the tire. The tread has a belt consisting of at least two plies of metal cords rigidly reinforcing just below the tread in an intersecting arrangement at a small angle to the tire. The tread main groove has continuous or discontinuous zigzag circumferential ribs defined by grooves, and the tread main groove includes one or a pair of central circumferential main grooves disposed in the central area of the tread, Heavy load air comprising a pair of side circumferential main grooves that partition outer ribs and a pair of intermediate circumferential main grooves arranged between the center circumferential main groove and the side circumferential main groove. In the tire, the central circumferential main groove is symmetrical, with the groove wall having an acute angle of 14 to 24 degrees with respect to the normal line of the tread passing through the groove edge in a cross section perpendicular to the groove wall. The intermediate circumferential main groove similarly has a groove wall inclination in the form of a broken line in which the inclination angle in the radially inner part of the groove wall is larger than that in the radially outer part. The side circumferential main groove has a laterally symmetrical cross-sectional shape, and the side circumferential main groove also has a laterally asymmetrical cross-sectional shape in which the inclination angle of the axially outer groove wall is larger than that of the axially inner groove wall. This is a heavy-duty pneumatic radial tire characterized by having: The present invention will be explained in detail below using the drawings. The tread pattern of the tire of this invention itself is
An example of this is shown in Figure 3, which is the same as that of a conventional tire.
one or a pair of central circumferential main grooves 1 (not shown) disposed in the central region of the tread Tr, and a pair of side circumferential main grooves 3 that partition the outermost ribs 6 of the tread Tr.
and a pair of intermediate circumferential main grooves 2 disposed between these, there are five or six tread main grooves extending in a zigzag shape in the circumferential direction. The directional ribs 4, 5, 6 are additionally arranged with thin grooves extending in the circumferential direction with a narrow width (approximately 2% or less of the tread width), and as already mentioned, the circumferential ribs 4, 5, 6 are arranged with lateral grooves. Dividing in the circumferential direction does not affect the essence of the invention. Note that when a pair of central circumferential main grooves 1 are provided, they may be arranged at approximately symmetrical positions narrowing the center circumferential line of the tire, as in the usual case. Now, FIGS. 4a, b and c show the main tread grooves of the tire according to the present invention shown in cross-sections perpendicular to the groove walls as shown in A-A, B-B and C-C in FIG. 3, respectively. It has a cross-sectional shape. Figure 4a shows the cross-sectional shape of the central circumferential main groove 1, in which the inclination angle _α1 of the groove wall 1', which forms an acute angle to the normal line of the tread Tr passing through the groove edge, is relatively large. The cross-sectional shape is bilaterally symmetrical. In the central circumferential main groove 1, stones are particularly likely to form when driving on rough roads, and therefore the above-mentioned inclination angle _α1 of the groove wall 1' is made relatively large. The angle α ₁ is preferably between 14 and 24 degrees, more preferably between 17 and 21 degrees. In addition, the inclination angle of the groove wall shall be in accordance with the standards defined above under the condition of normal internal pressure filling and no load.
The same applies to each of the circumferential main grooves in the intermediate portion and side portions below. Speed 30KM/H per tire size 10.00R20
As shown in FIG. 5, the results of a field test of driving on rough roads show that when the inclination angle of the groove wall 1' is 14 degrees or more, the effect of preventing rock formation is remarkable. If the angle is larger than 24°, the occurrence of railway wear may become so large that _it cannot be ignored. desirable. Figure 4b shows the cross-sectional shape of the intermediate circumferential main groove 2, where the inclination angle α ₂ of the radially inner part 2' _-I of the groove wall is the inclination angle β of the radially outer part 2' _-0 . The groove wall has a symmetrical cross-sectional shape having a broken line shape, that is, a two-stage groove wall inclination angle. In the intermediate circumferential main groove 2, railway wear is particularly likely to occur in the early stages when the vehicle is running on a good road, and rock formation is likely to occur when the vehicle is running on a rough road.Therefore, the cross-sectional shape described above is adopted. The angle β is preferably 0 to 10 degrees, more preferably 4 to 8 degrees, and _α2 is 14 to 24 degrees, more preferably 17 to 21 degrees. The amount of railway wear represented by the step difference δ (see Figure 1) decreases as the inclination angle of the groove wall decreases, as shown in Figure 6 (results of continuous running on good roads) for the above sample tire. However, since the effect of reducing railway wear or delaying its onset is particularly significant when the angle is less than 10°, the inclination angle β of the radially outer portion 2' _-0 of the groove wall of the intermediate circumferential main groove 2 is The angle is preferably 10° or less. However, if it is less than 0°, manufacturing becomes difficult and there is a risk that the rib ends may be chipped, which is not preferable. Furthermore, the ratio of the height h of the radially outer portion 2' _-0 to the depth D of this groove 2 is determined to prevent railway wear and stone entrapment.
Considering the balance between the two, preferably 5 to 50%,
More preferably, it is 20 to 40%. FIG. 4c shows the cross-sectional shape of the side circumferential main groove 3, and shows the axially outer groove wall 3' facing the outermost rib 6.
The groove wall _3' has an asymmetrical cross-sectional shape in which an inclination angle α3 of _-6 is larger than an inclination angle γ of the axially inner groove wall 3' _-5 facing the rib 5. In the side circumferential main groove 3, when running on a good road, railway wear occurs on the rib end 5-3 adjacent to the axially inner groove wall 3' _-5 , and railway wear occurs on the rib end _5-3 adjacent to the axially outer side of the main groove 3. Since wave-like wear is likely to occur in the outermost rib 6, the groove shape described above is formed. The angle α ₃ is preferably 14-24°, more preferably 17-21°, and the angle γ is preferably 7-17°.
°, more preferably 10 to 14 °. The amount of wavy wear (step) δ' (see Fig. 2) that occurs at the outer end 6 _-0 of the outermost rib 6 is the same as that of the side circumferential main groove 3, as shown in Fig. 7 as the result of the steady rotation test. It decreases as the groove wall inclination angle increases, and when it is set at 14 degrees or more, the reduction effect is significant, and when it is set at more than 24 degrees, the occurrence of railway wear may become impossible to ignore. Axial outer groove wall 3'
The inclination angle _α3 of _-6 is preferably within the above range. In addition, as mentioned above, railway wear is likely to occur on the axially inner groove wall 3' _-5 , but the occurrence of stone build-up during driving on rough roads cannot necessarily be ignored in this side circumferential main groove 3 as well. Therefore, taking both of these into consideration, it is preferable that the inclination angle γ of the groove wall 3'- ₅ is set within the above range. Next, we will show the results of a comparative test that clarified the effects of this invention. The test tire had a size of 10.00R20 and consisted of a carcass consisting of at least one ply with cords arranged in the substantial radial plane of the tire, and a carcass surrounding the carcass and intersecting at a relatively small angle with respect to the circumferential direction of the tire. This is a heavy-duty radial tire that has a belt consisting of at least two plies of metal cords that rigidly reinforces the area just below the tread in an array, and the tread pattern consists of six cords of approximately equal width as shown in Figure 3. It has five main tread grooves so as to limit the circumferential ribs. Center circumferential main groove 1, middle circumferential main groove 2, side circumferential main groove 3
have the groove shapes shown in FIG. 4a, b, c, respectively, and the angles α ₁ , α ₂ , β, α ₃ , γ and the ratio h/
D is 18°, 20°, 7°, 20°, 13° and
It was set to 0.3. On the other hand, the control tire used for comparison had the groove shapes of the tread main grooves 1, 2, and 3 all the same as shown in Fig. 4a, in which the groove wall inclination angle _α1 was 14 degrees. It has exactly the same structure as the tire of the present invention described above. Both tires have an internal pressure of 7.25Kg/cm ² and 20,000km under normal load (of which, good roads: 90%, speed 60km/h; bad roads: 10%, speed 30km/h)
Km/h) After traveling, the number of stone chips, amount of railway wear (step) δ, and amount of wavy wear (step) δ' were measured. The following results are shown in the following table. The numerical values are expressed as an index with the comparative tire set as 100.

[Table] As is clear from the results, the tire of the present invention was able to advantageously and effectively prevent uneven wear and stone build-up over almost the entire tread surface compared to the comparative tire. Although the amount of railway wear at the inner end 4 _-1 of the rib 4 of the tire of the present invention is somewhat increased compared to the comparative tire, the absolute amount of railway wear at this portion itself is small and can be ignored. It is. As described above, the present invention improves the shortcomings of conventional products and achieves remarkable effects in preventing uneven wear and stone build-up in heavy-duty radial tires that are forced to be used on both good and bad roads. Is possible.

[Brief explanation of the drawing]

Fig. 1 is a partial meridional cross-sectional view of a tire showing the occurrence of railway wear, and Fig. 2 is a partial external view of the tire viewed from the axial direction showing the occurrence of wave-like wear.
Fig. 3 is a developed view showing the tread pattern of the tire, Fig. 4 a, b, and c are Fig. 3 A-A, respectively.
A cross-sectional view of the tire groove of the present invention along lines B-B and C-C, FIG. 5 is a graph showing the relationship between the inclination angle of the groove wall and the number of stones, and FIG. 6 is the inclination of the groove wall. FIG. 7 is a graph showing the relationship between travel distance and railway wear amount using angle as a parameter, and FIG. 7 is a graph showing the relationship between groove wall inclination angle and wavy wear amount. 1... Central part circumferential main groove, 2... Middle part circumferential main groove, 3... Side circumferential main groove, 4, 5, 6... Circumferential rib, 4 _-1 , 4 _-2 , 5 _-2 , 5 _-3 , 6 _-3 , 6 _-0
...Side ends of circumferential ribs, 1', 2' _-1 , 2' _-0 ,
3' _-5 , 3' _-6 ...Groove wall, T...Tire, Tr...Tread, α ₁ , α ₂ , β, α ₃ , γ...Inclination angle of groove wall, h...Middle part circumference The height of the radially outward portion of the groove wall of the direction main groove, D...the depth of the intermediate circumferential main groove.

Claims (1)

[Scope of Claims] 1. A carcass consisting of at least one layer of braais in which cords are arranged in the radial plane of the tire, and a carcass surrounding the carcass and directly under the tread in a criss-cross arrangement at a small angle with respect to the circumferential direction of the tire. The tread has a belt made of at least two plies of metal cords that rigidly reinforces the tread, and the tread has a continuous or discontinuous tread groove defined by a plurality of tread main grooves extending in a zigzag shape along the circumferential direction of the tire. The tread main groove has a zigzag circumferential rib, and the tread main groove includes one or a pair of central circumferential main grooves disposed in the central area of the tread and a pair of side circumferential grooves that define outermost ribs of the tread. A heavy-load pneumatic radial tire comprising a directional main groove and a pair of intermediate circumferential main grooves disposed between the center circumferential main groove and the side circumferential main groove, The direction main groove has a symmetrical cross-sectional shape with the groove wall having an acute angle of 14 to 24 degrees with respect to the normal line of the tread passing through the groove edge in a cross section perpendicular to the groove wall, and the intermediate portion The circumferential main groove similarly has a symmetrical cross-sectional shape with a broken line groove wall inclination in which the inclination angle in the radially inner part of the groove wall is larger than that in the radially outer part, and Similarly, the side circumferential main groove has an asymmetrical cross-sectional shape in which the inclination angle of the axially outer groove wall is larger than that of the axially inner groove wall. radial tire. 2. Each inclination angle of the radially inner part of the groove wall of the intermediate circumferential main groove and the outer groove wall of the side circumferential main groove is
The tire according to claim 1, which has an angle of 14 to 24 degrees. 3. The tire according to claim 1 or 2, wherein the radially outer portion of the groove wall of the intermediate circumferential main groove has an inclination angle of 0 to 10 degrees. 4 The inclination angle of the inner groove wall of the side circumferential main groove is 7.
The tire according to claim 1, 2 or 3, wherein the angle is -17°. 5 The radially outer portion of the groove wall of the intermediate circumferential main groove is 5 to 50 mm deep from the tread to the depth of the intermediate circumferential main groove.
%. Tire according to claim 1, 2, 3 or 4.