JPH0227162B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic tire for use on icy roads that has a tread portion that improves frictional resistance (traction performance) on roads covered with snow or ice in winter. The coefficient of friction of a tire on a road surface covered with snow or ice is considerably smaller than that on an ordinary paved road surface. To prevent slipping when driving on slippery roads,
Conventionally, the following tires (1) to (5) have been proposed. (1) A tire covered with a mainly metal chain. (2) Tires with a tread pattern that has a large coefficient of friction with snow or ice. (3) A tire with steel wire inserted into the tread. (4) Tires with spikes etc. driven into the tread. (5) Tires made of treaded rubber, which has a high coefficient of friction with snow or ice. However, while tires of types (1), (3), and (4) above generally have relatively good traction performance on snowy and icy roads, they emit noise and have poor ride comfort, and they also have poor ride quality on non-snowy roads. Severe road surface damage has become a major social problem. Furthermore, it is difficult for the above-mentioned type (2) of tires to significantly improve the traction performance, especially on ice and compacted snow. Therefore, the tire of type (5) above is most desirable as a tire that satisfies the social demand for reducing road surface damage and exhibits relatively good traction performance on snowy and icy roads. Therefore, the present invention has been made to further improve the traction performance of the tire of type (5) above, and as a result of various studies including the mechanism of generating frictional resistance in tires on ice and compacted snow. This was achieved by partially constructing the tread portions using different types of rubber compounds with different thicknesses. That is, the pneumatic tire for icy and snowy roads of the present invention is a pneumatic tire having a tread portion constituted by blocks divided by main grooves, in which the blocks in the central region of the tread are
The tread is made of flexible rubber having a JIS hardness of 68 or less, and at least a portion of the blocks in each tread end region adjacent to the tread center region are made of a harder rubber than the blocks in the tread center region. shall be. The resistance that tires experience when they slide on a snowy and icy road surface can be broadly classified into the following two types, considering the mechanism by which it occurs. (a) Frictional resistance between the tread surface and the snow and ice road surface. (b) Resistance when the edges of the blocks in the tread section sink into the snow and ice road surface and mechanically destroy the snow and ice road surface. In order to distinguish between these resistances, the resistance in (a) is hereinafter referred to as frictional resistance, and the resistance in (b) is referred to as mechanical resistance.
In a broad sense, the frictional resistance that tires experience on snowy and icy road surfaces, including these factors, is referred to as traction performance. Furthermore, traction performance can be broadly classified into static traction performance and dynamic traction performance. Static traction performance refers to the maximum traction when a stationary tire starts moving, and refers to the performance of whether or not a stopped vehicle can start on a snowy and icy road surface. If a vehicle is climbing a snowy and icy road and stops in the middle of a slope, and tires that do not have sufficient static traction performance are installed, the vehicle will not be able to start up and continue up the slope, and will be stuck. This is an important performance because it will be stored away. on the other hand,
Dynamic traction performance refers to the magnitude of traction when a running vehicle accelerates, turns, or brakes, and is a very important performance for use and safety. Hereinafter, an example of the tire of the present invention will be described in detail with reference to the drawings. FIG. 1 is a developed plan view of a tread portion of an example of the tire of the present invention, and FIGS. 2a and 2b are a meridional sectional view along the line L-- ₁ and a meridional sectional view along the line L-- ₁ , respectively. In these figures, reference numeral 1 denotes a tread portion, and this tread portion 1 is composed of blocks 3 divided by main grooves 2. In addition, 4 indicates a belt layer in which the cord is inclined at an angle of 10° to 30° to the tire circumferential direction, and 5 indicates a belt layer in which the cord is inclined at an angle of 70° to the tire circumferential direction.
6 represents a carcass layer inclined at 90°, 6 represents a sidewall portion, and 7 represents a bead portion. The width t _c of the tread center of the tread portion 1 is 1/2 of the tread width T, and the width t _s of the tread ends on both sides thereof,
Each t _s ' is 1/4 of the tread width T. The block in the center area of the 1/4T tread of this tread portion 1, which is centered on the tire equatorial plane, is at 0°C.
It is made of flexible rubber with a JIS hardness of 68 or less, and at least a portion of the blocks in each 3/8T width end area adjacent to the center area of the tread are more rigid than the blocks in the center area of the tread. It is made of hard rubber. The width of the central region of the tread where the flexible rubber is arranged is preferably at least 1/4 of the tread width T in order to improve traction performance on ice. The mixing ratio of hard rubber in the tread section is 6 to 75.
%, more preferably 20 to 75%. If it is less than 6%, static traction performance on ice will not improve, and if it exceeds 75%, dynamic traction performance on ice will deteriorate, which is not preferable. Furthermore, if the mixture ratio exceeds 75%, the width of the tread center region cannot be maintained at least 1/4 of the tread width T. The mixture ratio is expressed as the ratio of the area of hard rubber in the ground contact area (non-groove area) to the total area of the area (non-groove area) that directly contacts the road surface when the tire touches the ground. JIS at 0°C for blocks in the central area of the tread
If the hardness exceeds 68 or if at least some of the blocks in the tread end area are less hard than the blocks in the tread center area, traction performance on ice and snow treads will be lower than that of conventional tires with tread areas made of the same rubber. I don't like it. In order to further improve dynamic traction performance on ice, it is preferable that the JIS hardness of at least part of the blocks in the tread end region be 73 or higher at 0°C, and the durability (block chipping, chipping, etc.) Taking this into consideration, it is more preferable that the JIS hardness at 0° C. be 73 to 90. In addition, the block in the center area of the tread has a JIS hardness of 68 or less at 0℃,
It is preferably in the range of 50-68. This is 68
As mentioned above, if it exceeds 50, the traction performance on icy and snowy treads will not improve, while if it is less than 50, the tread block will become too flexible and the rigidity of the tread block will decrease, resulting in poor maneuverability and wear resistance on non-icy and snowy roads. This is because the negative effects of Regarding the thickness of the hard rubber, considering the traction generation mechanism, the hard rubber part mixed in the end area of the tread does not necessarily need to be thick.
It is clear that as long as the hard rubber is exposed on the surface of the tread that comes into contact with the snowy and icy road surface, it will be able to penetrate into the road surface better. However, in order to maintain the original traction performance on snowy and icy roads even when the tire is worn out, it is desirable that the thickness of the hard rubber be at least half the groove depth when new. Another embodiment is shown in FIGS. 1-5. Fig. 3 1 shows the case where hard rubber is placed on both shoulder sides by 1/3 of the tread width T in the rib direction, t _c = t _s = t _s ′ = 1/
It is 3T. Figure 3-2 shows the case where hard rubber is placed on both shoulder sides at a constant width and at regular intervals in the lug direction by 1/3 of the tread width T, and t _c = t _s = t _s ′ = 1/
It is 3T. Figure 3 shows 1/3 of the tread width T at a constant width and at regular intervals in the 45° direction relative to the tire circumferential direction.
When hard rubber is placed on both shoulder sides, t _c = t _s = t _s ′ = 1/3T. Similarly, Fig. 3 and 4 show the case where hard rubber is placed on both shoulder sides at a constant width of 1/3 of the tread width T at regular intervals in the direction of 45 degrees with respect to the circumferential direction of the tire, and t _c = t _s. ＝t _s ′＝
It is 1/3T. FIG. 3 and 5 show the case where the central portion of each shoulder block is made of hard rubber with a cross section of a constant size. In these FIGS. 3, 1 to 5, hatched areas and grid line areas indicate the arrangement of hard rubber, and the arrangement of the hard rubber in the cross section of the tire is the same as in FIG. 2. Next, the circumstances leading to the present invention and experimental examples will be explained. Rubber hardness, which is one of the important material properties of treaded rubber, varies greatly depending on its compounding contents (types and amounts of reinforcing agents, oils, vulcanizing agents, etc.). The hardness of this tread rubber determines the tire's maneuverability, stability, cushioning (ride comfort), wear resistance,
It has a very large effect on friction performance, etc., and
The desirable hardness of rubber from the viewpoint of each performance differs depending on the target properties. Therefore, the hardness of the tread rubber is generally determined by taking into consideration the balance between various performance levels of the tire and the design target levels. The hardness of this treaded rubber is
It also has a very large effect on the friction performance of the tire. In other words, when the tread rubber is soft, it adheres well to the snowy and icy road surface, increasing the contact area and improving dynamic traction performance.On the other hand, when the tread rubber is hard, it often embeds into the snowy and icy road surface, improving static traction performance. The present invention was made by understanding the relationship between the hardness of tread rubber and traction performance on snowy and icy roads. Table 1 below shows the compounding contents of various rubbers with different hardness, and four of them were made into treaded rubber.
The results of static and dynamic traction performance tests of 165SR13 tires on snow and icy roads are shown. The rubber hardness was measured using a spring-type hardness tester type A at 30°C and 0°C using the method specified in JIS K6301. becomes important. In the following, unless otherwise specified, rubber hardness refers to that at 0°C. Also,
The tire performance was tested using the method described below. Static traction force test on snow: Two vehicles are connected with a wire rope via a load cell on a compacted snow road surface, and test tires are attached to the drive wheels of the tow vehicle. With the rope between the vehicles still attached and both vehicles stopped, the brakes of the towed vehicle are applied, and the drive torque of the test tires of the towed vehicle is gradually increased until the maximum drive is reached until the tires finally spin. The force was measured. (Each tire was measured five times.) Here, the maximum driving force of each tire is expressed as an index using the following formula, using the value of the tire with treaded rubber B as a reference. Maximum driving force of each tire/maximum driving force of tire of tread rubber B x 100 Static traction force test on ice: The test method was the same as the static traction force test on snow, except that the test road surface was an ice surface. Braking test on snow: On a snowy road surface, from an initial speed of 40 km/h, all four wheels are suddenly braked and locked, the test vehicle is stopped by applying the brakes, and the distance from the point where the brakes are applied to the point where the vehicle stops is measured. is measured and expressed as an index using the following formula using the value of the tire with treaded rubber B as a reference. Braking stopping distance of tire of tread rubber B/braking stopping distance of each tire x 100 The measurement of each tire was repeated five times. Braking test on ice: The test method is the same as the braking test on snow, except that the test road surface is ice.

[Table] From Table 1, it can be seen that the dynamic traction performance on snow and ice is better when the tread rubber is flexible, but the static traction performance on snow and ice is better when the tread rubber is hard. This tendency is particularly noticeable on ice rather than on compacted snow. In other words, the traction performance on snowy and icy roads is
It is said that it is better if the treaded rubber is flexible,
In terms of static traction performance, we discovered the surprising fact that the harder the tread rubber, the better. This result reminds us of the following fact. In order to evaluate the static traction performance of a snow tire installed on a car on a snowy and icy road surface, after conducting a static traction test, the part where the tire was in contact with the ground (depending on the hardness of the road surface) (Although there is a difference in depth), there are always traces of the tread pattern left, and they are more visible than the traces left on the road surface after driving through snow and ice. In other words, for static traction on snowy and icy roads,
While the aforementioned mechanical resistance makes a large contribution, in the case of dynamic traction, the contribution of frictional resistance with the tread surface is large, resulting in the results shown in Table 1. Here, if the tread rubber is hard, it is unacceptable for the dynamic traction performance to deteriorate due to safety concerns, but the static traction index, which is one of the main factors in tire traction performance on snowy and icy roads, It is a fact that cannot be overlooked that is so high. Therefore, we conducted further research in order to create a tire that combines the dynamic traction performance of flexible rubber with the static traction performance of hard rubber. As mentioned earlier, there are two types of traction that tires experience on snowy and icy roads: mechanical resistance and frictional resistance. In the first place, within the contact surface of a tire tread, even when looking at the ground contact pressure distribution, the tread edge (shoulder part) is relatively high and the tread center is relatively low (this is due to the tire structure such as bias tires and radial tires). It is a generally widely accepted fact that all parts of the contact surface share the same mechanical resistance and frictional resistance. It doesn't necessarily mean that you are doing it. The tread end (shoulder part) is
Since the ground pressure is relatively high, the penetration into the snowy and icy road surface is deep, so it is thought that the mechanical resistance is relatively large. Therefore, the harder the rubber at the tread end (shoulder part) of the tread (shoulder part), the more the mechanical resistance of the tire will increase.
It is estimated that the traction performance of the tire will be improved. On the other hand, since the ground pressure at the center of the tread is relatively low, it is thought that the frictional resistance between the block surface of the tread and the snowy and icy road surface is relatively greater than the mechanical resistance caused by digging into the snowy and icy road surface. Therefore, the more flexible the rubber in the center of the tread, the greater the frictional resistance (because it deforms more easily and better adheres to the snow and ice road surface), and as a result, the tire's traction performance improves. Based on the above idea, within the same tored plane,
We prototyped tires using a mixture of various rubbers with different hardnesses, and confirmed through actual vehicle tests on ice that the arrangement of the different rubbers had better static and dynamic traction performance than conventional tires, as shown below. 165SR13 was used as the test tire, and tires having treads in various arrangements as shown in FIGS. 1-2 and 1-9 in FIGS. 3 were tested. The results are shown in Table 2 below.

【table】

[Table] The various tires shown in Figures 1 to 2 and Figures 3 to 9 are made by cutting unvulcanized rubber sheets into appropriate sizes and assembling them together as treads. there was. Rubber B (JIS hardness 62 at 0°C) and Rubber D (0°C) are shown in Table 1 as two types of rubber with different hardness.
JIS hardness (73) at The static and dynamic traction coefficients of tires with a mixed layout and only rubber B (relatively soft rubber) tread are expressed as an index with each of them set to 100, and the static and dynamic traction performance is evaluated. did. Compared to the standard conventional tire in which the tread rubber was only relatively flexible rubber B, the tires of the present invention of Examples 1 to 6 had a mixture of flexible rubber in the center region of the tread and hard rubber D in the end region of the tread. , all have excellent static traction performance, and what is noteworthy is that their dynamic traction performance is equal to or better than that of the standard conventional tire.
This is due to the uneven distribution of mechanical resistance and frictional resistance within the tread plane.
This confirms the correctness of the assumption that the tread end region contributes a large proportion to mechanical resistance, and the tread center region contributes a large proportion to frictional resistance. Also, according to Figure 4, which is a graph of the values in Table 2,
Mixing ratio is 6-75% or more, more preferably 20-75%
It is confirmed that 75% is more preferable in terms of static and dynamic traction. In addition, the fourth
In the figure, l indicates a preferable range of the mixing ratio. Next, with the structure shown in Figures 1 and 2, we fixed the rubber at the end of the tread at D (rubber hardness 73 at 0°C) and changed the rubber at the center of the tread. The static traction performance is shown in FIG. 6, respectively. As is clear from Figure 5, in order to improve static and dynamic traction performance on ice, it is necessary to
It can be seen that rubber with a JIS hardness of 68 or less must be used. Next, static and dynamic traction performance was confirmed when rubber with different hardness was placed at the ends of the tread, with the rubber hardness at the center of the tread constant.
The arrangement of the rubber at the center of the tread and at the ends of the tread is as follows:
Embodiment 1 shown in FIGS. 1 and 2 (t _c =T/2, t _s =t _s '
= T/4), the rubber at the center of the tread was fixed at C (JIS hardness 68 at 0°C), and the rubber at the end of the tread was changed to A to F shown in Table 1. Static and dynamic traction performance were compared. The results are shown in FIGS. 7 and 8. From Figures 7 and 8, it can be seen that for both static and dynamic traction performance, it is better for the rubber at the tread end to be harder than the rubber at the center of the tread, and in particular, the rubber at the tread end is JIS at 0°C. hardness 73
It can be seen that the above is more preferable. Also,
Rubber E and rubber F have different blends in terms of polymer, amount of carbon, and amount of oil, but at 0°C
The hardness of the rubber is the same. And the 7th and 8th
As can be seen from the figure, if the hard rubber placed at the tread end has the same hardness, the shearing performance on snowy and icy road surfaces will be almost the same regardless of the compounding content. This is natural because the traction contributed by that part (tread end) has a larger mechanical resistance. As described above, the tire of the present invention focuses on the difference in the traction generation mechanism on a snowy and icy road surface between the shoulder portion and the crown portion within the tread plane, and
By mixing rubber of different hardness suitable for each part on the same tread surface,
Its practical value is extremely high, as it was able to demonstrate better traction performance on snowy and icy roads than conventional tires.

[Brief explanation of drawings]

FIG _. 1 is _a plan development view of the tread portion of an example of the tire of the present invention, FIGS. Figures 1 to 9 are developed plan views of the tread portions of various tires in which hard rubber is arranged in various proportions, Figure 4 is an explanatory diagram showing the relationship between the mixing ratio of hard rubber and traction as a graph, and Figure 5 Figure 6 is a graph showing the dynamic traction performance when the rubber at the tread end is kept constant and the rubber at the center of the tread is changed. Figure 7 is a graph showing the dynamic traction performance when the rubber at the end of the tread is changed while keeping the rubber at the center of the tread constant. FIG. 2 is an explanatory diagram showing the target traction performance in a graph. 1...Tread portion, 2...Main groove, 3...Block, 4...Belt layer, 5...Carcass layer, 6...
Sidewall part, 7...Bead part, T...Tread width.

Claims (1)

[Claims] 1. In a pneumatic tire with a tread section composed of blocks divided by main grooves, the blocks in the central region of the tread are
The tread is made of flexible rubber having a JIS hardness of 68 or less, and at least a portion of the blocks in each tread end region adjacent to the tread center region are made of a harder rubber than the blocks in the tread center region. A pneumatic tire for icy and snowy roads.