JPS622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a tire tread for a construction vehicle that has a groove shape that reduces clogging of stones in the groove of the tread portion of a pneumatic construction vehicle tire. Conventional tires for construction vehicles have particularly lacked consideration for stone clogging. in the first place,
Due to the environment in which construction vehicle tires are used, stones tend to become clogged in the tread grooves. This stone clogging not only impairs traction performance, but also damages the bottom of the groove in some cases, resulting in a shortened tire life. Therefore, with the aim of eliminating this stone clogging, the inventor investigated the factors that cause stone clogging in conventional tires for construction vehicles, and found that the position where stone clogging occurs is 1 point from the center of the width of the tread. They are concentrated up to the /8 point, but especially around the 1/4 point (see Figure 1). This is because the shoulder part has a large movement of the tread pattern lugs, so there is less chance of stone clogging. As shown in Figure 1, the positions of the 1/4 point and 1/8 point above indicate the division points on the surface of the tread in the axial cross section of the tire, where C is the center of the tread, and S is the center of the tread. is the shoulder part, TR is the tread radius, and 1/4 is the dividing point where the width of the tread part is divided into 1/4.
It is the position of 1/4 point, and 1/8 is the position of 1/8 point of the dividing point that is also divided into 1/8. Note that it is not preferable for the tread radius TR to exceed three times the total width of the tire. Therefore, by devising the shape of the groove from the center C of the tread part to the 1/8 point, especially the groove shape of the main groove between the center C and at least the 1/4 point. This study revealed that the incidence of stone clogging is reduced. In other words, since the tire contacts the ground first at the center and then gradually moves toward the shoulder, it is preferable to increase the groove width from the center to the shoulder. This is preferable from the other point of view of heat generation during running of the tire, as it improves the heat dissipation effect on the shoulder side where the tread is thicker. Therefore, although tires for ordinary construction vehicles are made with wider grooves on the shoulder side than on the center side, the shape is not designed with stone clogging in mind; The degree of increase was also small, and no measures were taken to prevent stone clogging. Therefore, the inventor has determined that the groove shape coefficients are the increase rate γ of the groove width on the tread surface and the increase rate ν of the groove cross section.
This study determined the shape of the stone to prevent stone clogging. Fig. 2 shows the intersection angle of the grooves showing an example of an increase in the groove width of the main groove G, where α ₁ and α ₂ are the tread angles of the main groove whose inclination increases in the shoulder direction from near the center of the tread portion. This is the intersection angle between the groove width lines in the inclined direction on both sides of the groove on the face surface and the tire circumferential direction, and α
₁ > _α2 . The horizontal axis in the direction of the arrow indicates the tire axial direction, and the vertical axis indicates the tire circumferential direction. Figures 3-a and b illustrate groove cross-sectional shapes, and show inclination angles that indicate an example of increase in groove cross-section, and θ ₁ and θ ₂ are inclination angles between the groove wall surface and the vertical line. . By varying the intersecting angle and inclination angle of the grooves, a groove shape factor for preventing stone clogging was determined, and a groove shape suitable for the tread portion of a construction vehicle tire was set. Next, the increase rate γ of the groove width, which is the groove shape coefficient, and the increase rate ν of the groove cross section, which is the groove shape coefficient, will be explained. In other words, the increase rate γ of the groove width on the tread surface is
was calculated using the following formula. γ=tanα ₁ −α ₂ /2 . . . Formula 1 In the formula, α ₁ and α ₂ are the intersection angles shown in FIG. The increase rate ν of the groove cross section was determined by the following equation. ν=tanθ ₁ +θ ₂ /2 (2) where θ ₁ and θ ₂ are the inclination angles shown in FIG. Next, the test method and test results are shown. We manufactured 1800-25, 32PR tires without tread patterns, hand-carved grooves with various groove shape coefficients on the treads, and installed them on construction vehicles to investigate the degree of stone clogging. Next, Table 1 shows the groove shape coefficients of the test tires.

[Table] Next, tires having the various groove shape coefficients shown in Table 1 were installed on the cars of three users (all tires were installed on the outside of the rear wheels) and evaluated. The evaluation method was to count the number of stones stuck in the 20 main grooves. The results are shown in Table 2 below.

[Table] As shown in the results of Table 2 above, groove classification D,
E, G, H, and J have excellent stone clogging prevention effects. Therefore, it was found that if γ×ν≧0.05, stone clogging would be extremely reduced. Therefore, the main groove G is designed to have a shape that satisfies the condition γ×ν≧0.05 within the range of the groove width increase rate γ < 0.5 of the groove shape coefficient and the groove cross section increase rate ν < 0.5 of the groove shape coefficient. By doing so, it is possible to prevent stones from clogging the groove, which has the effect of increasing the durability life. Figure 4 shows the range* marked where stone clogging is unlikely to occur, and the vertical axis represents the rate of increase in groove width γ;
The horizontal axis indicates the rate of increase ν of the groove cross section. The figure is a graphical representation of the results in Table 2, where the asterisk (*) indicates the area with less stone clogging, and the diagonal line indicates the range where stone clogging is less likely to occur.

[Brief explanation of the drawing]

FIG. 1 is a dotted view of the surface of the tread portion in the axial cross section of the tire. Fig. 2 is a diagram of the intersection angle of the groove between the groove width line and the tire circumferential direction, Fig. 3 is a diagram of the inclination angle of the groove cross section, and Fig. 4 is a diagram of the relationship between the groove shape coefficients γ and ν. . C: Center of the tread in the axial cross section of the tire, G: Main groove, γ: Rate of increase in groove width of groove shape coefficient, ν: Rate of increase in groove cross section of groove shape coefficient.

Claims (1)

[Scope of Claims] 1. In a lug-type tire for a construction vehicle, the groove width line in the direction of inclination on both sides of the groove on the surface of the tread portion of the main groove whose inclination increases from near the center of the tread portion toward the shoulder and the circumferential direction of the tire. intersecting angle α ₁ , α ₂
, α ₁ > α ₂ , and from the intersection angles α ₁ and α ₂ , the increase rate γ of the groove width of the groove shape coefficient is determined by the following formula γ≦tanα ₁ −α ₂ /2, and the cross-sectional shape of the groove is: As shown in the figure, the inclination angles θ ₁ and θ ₂ between both side walls of the groove and the vertical line are formed, and the increase rate ν of the groove cross section of the groove shape factor is calculated using the following formula ν=tanθ ₁ +θ ₂ /2. , In the main groove between at least 1/4 point from the center of the tread part, the increase rate of the groove width of the groove shape factor γ < 0.5
A tire tread for a construction vehicle, characterized in that the main groove is set so that the groove shape coefficient product γ×ν≧0.05 within the range of the increase rate of the groove cross section of the groove shape coefficient ν<0.5.