JPH04201609A - Pneumatic tire excellent in running performance on frozen and wet ground surface - Google Patents

Abstract

PURPOSE:To improve turning property on the surface of frozen and wet road by forming a narrow width land section and a wide width land section which are narrow grooves which tilt in the direction of width of stepping face at the predetermined angle and have the predetermined wall thickness respectively in a land section which consists of a main groove and an auxiliary groove, and setting thickness of the land section which is orthogonal to the narrow groove to the predetermined thickness in a studless tire. CONSTITUTION:A tread face 1 consists of main grooves 2 and auxiliary grooves 3 to form land section divisions 4. Further, a narrow groove 5 which tilts at the inclination angle theta1 of 45 deg. or more for the direction of width of the stepping face 1 is formed in each land section division 4 to divide into a narrow width land section 6 and a wide width land section 7. Average thickness T which is measured in the orthogonal direction of groove wall of the narrow groove 5 of the land section division 4 is set to 1.5 times or more thickness from the bottom of the narrow groove 5 to the bottom of a mutually divided groove 2. Also, wall thickness TS of the narrow width land section 6 is set to 0.1 to 0.5 times depth h of the narrow groove 5, and thickness TL of the wide width land section 7 is set to 0.78 times or more depth (h) of the narrow groove 5, respectively.

Description

[Detailed Description of the Invention] (Industrial Application Field) Tires such as studless tires used for vehicles running on snowy or frozen ground have strong grip performance on the snowy layer on the ground. Therefore, it is desirable to have a tread pattern that exhibits effective traction, braking ability, and turning ability even on frozen surfaces and frozen road surfaces caused by crushing and melting of the snow layer.

This invention can be used not only in general applications such as passenger cars, but also in
It can be used as an effective countermeasure against snow, including when installed on heavy vehicles such as trucks and buses, and it not only provides traction and braking ability on icy surfaces and frozen roads, but also has the necessary ability when turning. This paper proposes the results of research and development on a tread pattern that can demonstrate unique abilities.

(Prior art) Conventional measures to improve the running performance of tires on icy surfaces and frozen roads generally include arranging narrow grooves called sipes or slits in the ridges that make up the tread pattern. It is customary to enhance the edge effect formed on the tread surface by
508 and Japanese Patent Application Laid-open No. 1-106704). By the way, if a large number of sipes or slits are used as required for this purpose, not only will this result in a decrease in tread rigidity, which will have a negative effect on traction, but will also reduce the contact area due to bending deformation of the ridges. The melt water caused by the local pressure rise there actually deteriorated the braking performance on frozen surfaces.

Regarding this point, for example, Japanese Patent Application Laid-Open No. 2-212204 discloses that heel-and-toe wear can be prevented from occurring in the front stage of the sipes by arranging the sipes in a specific sparse arrangement. Therefore, a solution to avoid this problem is disclosed. However, in this technique, the aim is only to utilize lower rigidity between sipes with a narrow spacing as compared to between sipes with a wide spacing, and the use of stiffness between sipes is also mentioned. There is no mention of any ideas.

Further, all of the above-mentioned conventional techniques focus on improving traction and braking performance, and do not mention anything about improving turning performance (structure-slip resistance), which has been particularly desired in recent years.

(Problem R to be solved by the invention) The land sections, for example called blocks, constituting the tread pattern of the tire are arranged so that the sipes, i.e., the virtual closure between the groove walls within the contact area of the tire, occur between each other. The decrease in rigidity of the subdivided portions due to the narrow cut grooves (hereinafter simply referred to as narrow grooves) is due to the fact that the edges resulting from bending deformation of the portions can improve the tire's traction, braking performance, and turning performance. However, on the other hand, due to the tire load acting concentrated on such edges, the localized pressure increase increases the amount of frozen surface or melt water on the frozen surface, which actually reduces driving performance. SUMMARY OF THE INVENTION An object of the present invention is to appropriately avoid such disadvantages and, in particular, to propose a pneumatic tire suitable for running on wet, frozen ground that has a tread pattern that can significantly improve turning performance.

(Means for Solving the Problems) This invention provides a plurality of main grooves extending along the circumference of the tread, or a plurality of sub-grooves crossing the main groove, within the tread that touches and rolls on the running ground surface. mutually separated by grooves,
It has a large number of land sections that are separate and independent from each other, and at least some of the sections have groove depths that are equal to or less than the depth of the grooves that mutually separate the sections, and at an angle of 45 degrees or more with respect to the width direction of the tread. A narrow land section subdivided by two narrow grooves and a wide land section with a much narrower groove width having an angle of . The bending deformation area occupies the range of 0.1 to 0.5 times the groove depth of the narrow groove, and the wide width area measured perpendicular to the groove wall of the narrow groove. The thickness of the land part is 0.78 relative to the depth of the narrow groove.
The average thickness of the land section, measured perpendicularly to the groove wall of the narrow groove at the bottom of the mutually dividing groove, is calculated from the bottom of the narrow groove. A pneumatic tire that has a tread pattern that is 1.5 times or more thicker than the bottom of the mutually dividing grooves and has excellent running performance on wet and frozen ground, and the present invention provides: It is useful if the narrow land section has a height that projects above the tread of the land section by up to 0.2 times the groove depth of the narrow groove.

That is, in the present invention, at least a portion, in fact, most or all, of the land section is divided into a bending deformation region and a shear deformation region, and the edge effect due to the deformation of the bending deformation region is By maintaining and ensuring the contact area of the contact area under high rigidity (non-bending deformation) due to the deformation area, it can be used to perform more advantageously.

Figure 1 shows the main parts of an example of a tread pattern that can obtain a large frictional force in the width direction of the tread and its A.
- Shown in cross section A, number 1 in the figure is the tread, 2 is the tread l
3 is a minor groove that crosses the main groove 2; 4 is a land section that is mutually separated and independent from the main groove 2 and the minor groove 3; 5 is a land section that connects the land section 4 with each other; A narrow groove with a groove depth equal to or less than the groove depth of the dividing groove 2 or 3, and a much smaller groove width that forms an angle θI = 45' or more with respect to the width direction of the tread 1 (in this example, θ1 = 90°) )
, 6 is a narrow land area subdivided by narrow grooves 5, 7 is a narrow groove 6
This is a wide land area shown as an example where it is subdivided by sipes S according to the flow guidelines.

In addition, H is the groove depth of the main groove 2 or the sub groove 3 as mutually dividing grooves of the land section, whichever is deeper (usually the main groove is deeper or equivalent), and h is the groove depth of the narrow groove 5. Groove depth, T! is the thickness of the narrow groove ridge 6, TL is the thickness of the wide land portion 7, and T is the average thickness of the land section 4 at the bottom of the mutually dividing groove.

FIGS. 2(a) and 2(b) show another example according to the present invention, which is advantageous when improving not only turning performance but also traction and braking performance, and FIG. An example in which the narrow land portion 6 is made to protrude further is shown, and d in FIG. 3 is the protrusion margin of the narrow land portion 6.

(Function) Now, regarding the friction coefficient μ on the frozen surface, land section 4
The ground pressure distribution when this block is divided into narrow grooves 5 is shown at the edge part e in FIG.
It is obvious that it is desirable that the block be grounded as evenly as possible over the entire surface of the block. ■ in the figure indicates the direction of frictional movement of the tire. Here, the ground pressure distribution of the block can be changed by deforming the block, for example,
As shown in FIGS. 5(a) and 5(b), if the deformation caused by the frictional force F is a bending deformation, an edge portion e will stand up, whereas if it is a shear deformation, the ground plane will not rise.

Using a block model as shown in Figure 6, the block rigidity when a force is applied in the According to known literature, if the inclination angle at the tip of the block (ground contact part) due to deformation is θ2, then the following is given.If the shear force per unit ground contact area is f, then F=fbt, so around f the inclination angle θ2 Equation (1) above is the block stiffness when bending and shearing are included.If the bending stiffness is Gb and the shear opening property is Gs, the above equations (1) to (3) can be expressed as the block length When expressed with respect to t, it becomes as shown in Figure 7, and the block height h is constant (1
0m+a), the bending rigidity increases rapidly as the block length t increases, and the deformation mode becomes relatively shear deformation (the shear deformation is constant).

From the above, the only way to control block deformation in bending and shearing without changing the block height h is to change the block length.

Therefore, in Fig. 4, in order to make the edge part e high and obtain a ground pressure distribution in which the entire surface of the block is in contact with the ground as uniformly as possible in the remaining area, the edge part e must be deformed by bending, and the other parts must be deformed by shearing. Therefore, in the present invention, a thin block, that is, a narrow land portion 6 is arranged at the edge portion e of the land section 4, and the remaining portion, that is, a wide land portion 7 is separated from the narrow groove 5 to have a sufficient length. This not only improves traction and braking performance, but also increases the frictional force in the width direction of the tread 1 when the tire receives lateral force during turning.

In this invention, the narrow groove 5 is formed at an angle of 45° with respect to the width direction of the tread 1.
The reason for this angle is that it needs to be at least 45 degrees in order to obtain sufficient frictional force in the width direction of the tread 1 when the tire receives lateral force when turning. be.

Further, in the present invention, the wall thickness T8 of the narrow land portion 6 is limited to 0.1 to 0.5 times the groove depth h of the narrow groove 5, and the reason is as follows.

In other words, when the land section 4 subdivided by the narrow land section 6 rubs against the frozen surface, only the narrow land section 6 bends and deforms due to the frictional force, and its edge e is pressed against the frozen surface, causing the ice surface to bend. Scrape it off slightly. Then, the remaining land section 4 with large bending rigidity is placed on the fresh ice surface that appeared in the plow.
The bending deformation in this section is small, and the surface of the ridge is in almost uniform contact with the ground. Needless to say, under frictional conditions, melt water drifts on the ice surface, and the ice temperature rises, reducing the friction coefficient. By removing this melt water surface layer, the friction coefficient of the ice surface can be reduced. It becomes possible to obtain a large frictional force by increasing the height and applying friction on the ridges that touch the ground almost uniformly.

Here, as shown in Fig. 8, the bending rigidity of the land section is generally determined by the groove depth and the ridge thickness, but the above wall thickness T,
If it is thinner than 0.1 h, its rigidity will be too low, while if it is larger than 0.5 h, it will be difficult to form an edge, and in either case, the effect of scraping the ice surface will be reduced.

Furthermore, when the narrow land portion 6 is made to protrude from the surface of the land section 4, the effect of cutting the rice and wheat surface layer becomes even greater.

Next, the thickness TL of the wide land portion 7 is set to 0 of the groove depth h of the narrow groove 5.
．． The reason for this is limited to 78 times or more, as follows.

As already mentioned, the land section 4 adjacent to the narrow groove 5 must be in contact with the frozen surface as evenly as possible in order to generate a larger frictional force. The part must have high bending rigidity. Here, if the thickness TL of the wide land portion is less than 0.78h, the block will be deformed due to the decrease in block rigidity, and only the edge of the block will come into contact with the road surface, resulting in a decrease in the coefficient of friction. . In this invention, as a condition to avoid such problems and obtain a high coefficient of friction, the thickness TL of the wide land portion is limited to 0.78 h or more with respect to the narrow groove depth (sipe depth) h. did. In addition,
When the thickness TL of the wide width exceeds 2.07 h, the wide land area contacts the ground uniformly, but while the wide land area with the thickness TL rubs against the ice surface, a water film is generated due to the heat of Wl friction, and the coefficient of friction decreases. cause a decline. For this reason, it is preferable that TL be 2.07 h or less.

Further, the thickness TL of the wide land portion 7 described above is preferably at least twice the wall thickness Ts (7) of the narrow land portion 6 in order to provide a sufficient rigidity difference between the wide land portion 7 and the narrow land portion 6. .

Next, in this invention, the average thickness TI of the land section at the groove bottom of the mutually dividing groove measured in the direction perpendicular to the groove wall of the narrow groove 5 is calculated from the groove bottom of the narrow groove 5 to the mutually dividing groove. The thickness is limited to at least 1.5 times the thickness up to the groove bottom, and the reason for this is:
In the land section 4, when the surface layer S is from the tread 1 to the groove depth h of the narrow groove 5, and the base layer B is the area from the adjacent depth h to the main groove depth H, the height of the base portion B is The thickness Tll of the land section 4, which is the width of the base, is 1.5 of H-h.
When the bending rigidity is more than double, the bending rigidity becomes very large, and this part hardly deforms due to the frictional force, and the deformation of the base part B can be ignored (see Fig. 1). This also increases the stability of wide land areas.

In addition, as shown in FIG. 3, the narrow land section 6 is
The present invention is also applicable to cases in which the ice protrudes from the surface of the ice, but this allows for a greater cutting effect on the ice surface layer. However, if the amount of protrusion is too large, the protrusion will peel off during running, so the amount of protrusion must be 0.2 times or less the depth h of the narrow groove.

(Example) Test tires with a tire size of 10.0 OR 20 were prepared with the tread pattern according to the present invention shown in FIG. Prototypes were manufactured under the same conditions with the tire specifications other than those compared to the conventional patterns shown in the figure (reference tire), respectively, and fitted onto a rim of size 7.50VX20, with an internal pressure of 7.25kg/ A turning test was conducted under the conditions of "cm" and a load of 2,700 kg.

The turning test was conducted by turning around a disk-shaped course with a radius of 50 Ill on ice with an ice temperature of 15°C, and from the maximum possible turning speed (average speed during one lap around the course).
The following formula % formula %: R: radius of the course (a+) g: gravitational acceleration (9.8 m/s") Find the turning ice friction coefficient μ and calculate each value in index form, taking the performance of the standard tire as 100. A comparative study was conducted on the performance of tires on ice.

The results are shown in Table-1.

In addition, the speed with an index of 100 is 15.1/h,
The coefficient of friction μ on ice was 3.59×10−”.

1 ・ 1 ・; In the above description, the shape of the land division is schematically shown using a rectangular example, but in reality, it is shown in Figures 11(a) to 11(a).
Various shapes as illustrated in (f) can be arbitrarily selected, and the measurement procedure in such a case is as shown in the figure.

(Effects of the Invention) Thus, according to the present invention, the land section constituting the tread pattern has a melt water removal function that contributes to effective improvement of on-ice performance, and a function of ensuring frictional force between it and the frozen surface. By forming a bending deformation region and a shearing deformation region that share the same functions as the above, it is possible to more reliably improve running performance, especially turning performance, on frozen wet ground.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are developed views showing an example of the tread pattern according to the present invention, and their cross-sectional views. FIGS. Figure 4 is a cross-sectional view of the main part of the land section. Figure 5 (a) and (b) are comparison diagrams of bending and shear deformation. Figure 6 is a block model diagram. Figure 7 shows changes in rigidity with respect to block length. Figure 8 is a graph showing the relationship between block rigidity G and T/h. Figure 9 is a graph showing the conventional tread pattern. Figure 11 (a) to (f) are graphs showing the relationship between block rigidity G and T/h. It is a figure showing other examples according to. 1...Tread 2...Main groove 3...Minor groove
4...Land section 5...Narrow ditch
6...Narrow land area 7...Wide land area Fig. 1 (b) Fig. 2 (a) □ (b) Fig. 4 C Fig. 5 (a) (b) 6th flash t (fnfn ) Figure 9 Figure 1θ Figure 11 (C) (e) (b (d)

Claims (1)

[Scope of Claims] 1. A tread that contacts the ground and rolls on the surface of the running ground, which is mutually separated by a plurality of main grooves extending around the tread, or by these main grooves and a plurality of sub-grooves that cross them. At least some of the sections have a groove depth equal to or less than the groove depth of the grooves mutually dividing the sections, and have a groove depth of 45 mm in the width direction of the tread. A narrow land section and a wide land section are subdivided by at least one narrow groove having a groove width that is much narrower at an angle of at least 100 degrees. The measured wall thickness of the narrow land area is the bending deformation area that occupies a range of 0.1 to 0.5 times the groove depth of the narrow groove, and the wide width area that is also measured perpendicular to the groove wall of the narrow groove. It consists of a shear deformation region whose land thickness is 0.78 times or more the groove depth of the narrow groove, and was measured at the bottom of the mutually dividing groove in a direction perpendicular to the groove wall of the narrow groove. The average thickness of the land section is 1.5 times or more the thickness from the bottom of the narrow groove to the bottom of the mutually divided groove, and the driving performance is improved on a frozen wet ground surface with a tread pattern. Excellent pneumatic tire. 2. In claim 1, the narrow land portion has a height that projects above the tread surface of the land section by within 0.2 times the groove depth of the narrow groove.
A pneumatic tire with excellent driving performance on wet, icy surfaces.