JPS623001B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in motocross tires for motorcycles. Motocross is a motorcycle competition in which a set course is set on uneven terrain with many ups and downs, and participants compete for the number of laps on this course within a set time, or for the time required to complete a set number of laps. Unlike ordinary motorcycle tires that are used on paved roads, the motocross tires used have regular polygonal rubber blocks that are suitable for gripping the ground because the tire tread is used for running on mud and gravel. A so-called block pattern that stands out is usually applied. Conventionally, attention has been paid to the following two points when designing the tread of motocross tires. The first is the ratio between the space occupied between each block, which is the part that grasps mud or gravel during running, and the actual part of the blocks. In general, the smaller the space in the entire tread, the better in terms of wear of the block, but it reduces the essential ground grip and makes it impossible to achieve the desired purpose.On the other hand, if the proportion of the space increases, the ground grip Although the resistance tends to increase up to a certain limit, the overall volume of the block decreases, accelerating wear and tear, which has a negative impact on ground grip at the end of the competition. Second, due to the location where they are used and the unique tread pattern of the tires, motocross tires wear out much faster than regular tires that are used constantly on paved roads. As a countermeasure to this problem, an attempt was made to make the rubber of the block extremely hard in order to prevent the deterioration of running performance due to wear during use, but in this case,
It is inevitable that blocks will be missing or other performance degradation will occur. By the way, regarding the shape and arrangement of blocks,
Conventionally, a tread pattern has been known in which a plurality of blocks having square or rectangular outer surfaces are appropriately arranged parallel to the axis of rotation of the tire, and groups of blocks are arranged at regular intervals along the circumferential direction of the tread. ing. According to research conducted by the inventors, this type of tire, which is used on the driving wheel (usually the rear wheel), which is particularly important in motocross competitions, has a ratio of driving force to braking force that is applied to the tire during running. The ratio is 70:30, and the former is overwhelmingly more common.Therefore, the side of the block on which the driving force acts within the ground contact surface during driving, that is, the side of the block on the leading side in the direction of tire rotation, is larger. , there are more opportunities for the force to act at the above rate than on the opposite side of the block where the braking force acts, and when the car body is tilted to turn, that is, on a plane perpendicular to the horizontal plane. On the other hand, when the tires are in a position where their equatorial planes intersect (this angle of intersection is called the camber angle and can be as large as 40 degrees), a centrifugal force is generated in the horizontal direction on the car body, causing an increase in the distance between the tires and the ground. is accompanied by the occurrence of camber thrust to counteract this,
It has been found that within the block within the torpedo, it is the side of the block in a specific area that primarily receives this camber thrust. In view of these facts, the present invention aims to reduce the wear of the blocks and maintain effective ground gripping performance regardless of the progress of the wear. This invention includes a pair of bead parts, a toroidal carcass extending between these bead parts, and a large number of lateral grooves on the outer surface extending from the crown part of the carcass to both sides along the contour of the carcass. The tire has a tread consisting of a large number of blocks separated from each other by longitudinal grooves, and the centers of adjacent blocks within a group of blocks lined up in the width direction of the tread are shifted in the circumferential direction by 3 to 25 mm. The length of the outer surface of a block measured along the circumferential direction of the tread due to the mutual arrangement of block groups that include blocks of different steps and are arranged in the width direction with the longitudinal grooves between the blocks and the blocks between the longitudinal grooves overlapping each other via the lateral grooves. 20 of the tread circumference at any position in the width direction of the tread
~30%, and the overall block distribution is within ±0.05 of the change in block contact area/apparent ground contact area depending on the tire camber angle, and moreover, the main part of all blocks is A first side surface on which the driving force acts when driving on rough terrain, a second side surface located opposite to the first side surface, a third side surface on which the camber thrust of the tire also acts, and this third side surface on which the camber thrust of the tire acts. and a fourth side surface located on the opposite side of the side surface of No. 3, and the projected area of the side surface facing the direction in which the driving force and the camber thrust act, respectively, is larger than the second and larger than the fourth. A solution to the above problem is provided in the third case, each consisting of large blocks. Here, the ratio of the ground contact area of the block to the apparent ground contact area is defined later according to Fig. 7, and the amount of change in the value of this ratio according to the tire camber angle is the outer contour 19 in the figure It refers to the degree to which the ratio of the total area of the block surfaces occupying the contour to the area enclosed by the contour 19 changes as the camber angle changes. The explanation will be given below based on the drawings. FIG. 1 shows a block arrangement with a developed tread of a motocross tire according to the present invention, and FIG. 2 shows a cross section of the tire taken along the line A--A in the same figure. Number 1 in the figure indicates a tire, and a carcass 5 extends from the center tread 2 to both sides with the side parts 3 and extends in a toroidal shape between both bead parts 4 until it ends at the bead part 4. A plurality of rubberized fiber cord plies inclined at a constant angle with respect to O-O are stacked so that the cords cross each other between adjacent plies. In FIG. 2, the carcass is simply illustrated by drawing lines for convenience. The tread 2 extends substantially parallel to the contour of the carcass 5, and the tread ends E extend to both sides of the carcass 5. Therefore, the maximum tire width when the rim is assembled and filled with internal pressure is not expressed by the outer dimension between side parts 3-3, but by the distance between tread ends E-E. When a camber angle is given to the camber angle, the center of ground contact shifts from the equator O-O position when traveling straight to the side where the camber angle is given. This comes from the unique consideration given to tires. In FIG. 1, the tread 2 is formed from a large number of blocks 6 having several different shapes.
are block rows 6-1, 6-2, 6-3, 6-4 and 6 from the equator O-O position toward both sides, respectively.
-5 is placed. When tires are attached to the drive wheels of a vehicle, the direction in which the driving force acts on the tires is determined, and this is determined by the first direction.
It is indicated by arrow Y in the figure. On the other hand, when turning, the direction in which camber thrust acts is determined by arrow Z, for example, because if the camber angle is applied to the right side, the center of ground contact will shift to the right side.
If the camber angle is given to the left, the camber thrust acts in the direction shown by arrow Z' for the same reason. Therefore, among the blocks, for the block rows 6-1, 6-2 and 6-3 in the central region of the tread which are greatly affected by the driving force, the block width a on the side where the driving force acts is set to the opposite side (where the braking force is The block width b is wider than the width b of the block row 6-2 in FIG. 3 as a representative.
As shown in the cross section, the side surface 13 on the width a side has a larger projected area facing arrow Y than the side surface 14 on the width b side. The value of a/b measured in the direction perpendicular to arrow Y is preferably in the range of 1.1 to 1.5. In this embodiment, the widths of the side surfaces corresponding to the side surfaces 13 and 14 of the block rows 6-4 and 6-5 near the tread end E are equal when measured in the direction orthogonal to the arrow Y, but the widths of the block rows 6-4 and 6-5 near the tread end E are equal when measured in the direction perpendicular to the arrow Y. It is possible to use different widths with the same relationship as in cases 1 to 6-3. Next, each block has an outer surface 15 as shown in FIG.
The angle ε between the normal line passing through the edge of the vertically erected edge and the side surface 13
Similarly, it is preferable to make the angle δ smaller than the angle δ formed by the side surface 14, and it is more preferable to provide a difference in the range of 5° to 15°. Furthermore, for each block other than the central block 6-1, the length c of the block on the side on which the camber thrust acts, as indicated by arrow Z or Z', is longer than the length d of the block located on the opposite side. . c/
The value of d is preferably in the range of 1.1 to 1.3. FIG. 4 shows a CC cross section of the block 6-2, and by making the length c longer than the length d, the side surface 1 of the block on the length c side becomes the side surface 12 located on the length d side. The projected area facing the arrow Z or Z' is larger than that of the arrow Z or Z'. The angle β formed by the normal line passing through the edge of the block outer surface 15 and the side surface 11 is also preferably smaller than the angle γ formed by the side surface 12, and the difference should be in the range of 2° to 17°. is even more desirable. In Figures 3 and 4, the sides 13 and 1 of the block
The angles ε and β of 1 extend only over a distance corresponding to 20 to 40% of the depth from the outer surface 15 of the block to the base 7, and the remaining area on the base 7 side is the same as δ and γ. A large inclination angle can be achieved. Note that a and b mentioned above point to the arrow Y, that is, the equator O.
- block width measured perpendicular to O,
It goes without saying that c and d are the lengths measured in the direction perpendicular to the arrow Z or Z', that is, the rotational axis of the tire. Regarding the above, the total length of the block outer surface 15 measured along the circumferential direction of the tread may be within a range of 20 to 30% of the tread circumference anywhere between the tread ends E and E. is necessary. In this embodiment, the block row 6 is connected to the platform 8 which is raised from the base 7 by about 2.5 mm.
-1 and 6-3 and 6-5, or 6-2 and 6-
The blocks 5 and 5 are joined laterally, and a square cut 9 with a depth of about 2 mm is added to the outer surface 15 of each block, but such measures can be applied as appropriate depending on the tire size, application, etc. It shall be possible. Furthermore, although the side surfaces 11 and 13 are illustrated as planes extending perpendicular to the direction in which the force acts, it is also possible to form blocks by appropriately weaving zigzags, slopes, and curves. Figure 5 is Figure 1 D-D of the central block 6-1 row.
In this embodiment, the side surfaces 10, 10 of the block are inclined at mutually equal angles .alpha. with respect to the normal passing through the edge thereof erected on the outer surface 15 of the block. However, it is possible, for example, to arrange blocks having different inclined side faces at angles β and γ shown in FIG. 4 in alternating directions in the circumferential direction. The block having the above solid shape has a modulus of 70 to 160 kg/cm ² at 300% elongation, preferably 70
~140Kg/cm ² and shore A hardness is relatively low compared to normally applied 55 to 75 degrees, preferably 58 to 65 degrees.When applying tread rubber, the road grip is further improved. can be done. In the embodiment shown in FIGS. 1 to 5, the groups of horizontal blocks of the tread 2 are divided into individual blocks by longitudinal grooves 16, while transverse grooves 17
A group of blocks is divided in the circumferential direction by , and consists of two types of block groups 18-1 and 18-2 in which the centers of adjacent blocks within the group are shifted in the circumferential direction. Group of blocks 18-1 is in this example central block column 6-1.
The length c of the block belonging to block row 6-3 is calculated from the line J-J that bisects the length of the block belonging to
The line K-K (both perpendicular to the equator O-O) that bisects the block is shifted by f in the circumferential direction, upward in the figure, and similarly bisects the block L belonging to block row 6-5. -L is shifted downward by g with respect to line KK. Of course, this shift amount g can be shifted upward in the opposite direction to that shown in the figure. On the other hand, in the block group 18-2, the bisector line N-N of the block 6-4 is shifted downward by h steps with respect to the bisector line M-M of the blocks belonging to the block row 6-2. . The deviation amounts f, g, and h shall be selected as follows within the range of 3 to 25 mm. That is, the blocks are staggered circumferentially so as to provide a progressive increase in camber thrust support surface within groups of blocks next to the tread as the tire is successively given Kimber angles. It is also possible here that the offset of the step-shifting block be greater at positions closer to both sides of the tread. FIG. 6 shows an expanded version of the tread for another embodiment. In the embodiment shown in FIG. 6, the projected area in the direction of force action does not change between the side on which the driving force and camber thrust are applied and the opposite side of each side of each block arranged as a tread. Groups 18'-2 of blocks with different steps, which are largely shifted in the circumferential direction, are arranged alternately with groups of aligned blocks 18'-1, which have no difference in steps.
This focuses on consideration of camber thrust. In the figure, group 1 of the block with different steps
The blocks belonging to the central block row 6'-2 of 8'-2 and the blocks belonging to the both-side block rows 6'-4 are defined by the bisector of both blocks, that is, the length in the circumferential direction.
Straight line M'-M' and straight line N'-N' passing through each midpoint of d'-1 and d'-2 are significantly shifted by f' along the equatorial plane O-O. FIGS. 7a to 7e show changes in the ground contact profile when a tire to which the tread pattern shown in FIG. 1 is applied is pressed against a hard board surface and the camber angle is successively added. The outer contour 19 shown in this figure is obtained by applying stamp ink to the tire tread, sandwiching relatively thick white paper between it and a smooth hardboard, and pressing the tire onto this at various camber angles. This is an imaginary contour that connects the outer edge of the transferred trace of block 6 with a smooth curve. As shown in Figure 7, the camber angle is 10°, 20°.
When the angle is given as °, 30°, 40°, the camber angle becomes 0.
At 30°, the ground contact shape was a symmetrical elliptical shape, but it changed to an asymmetrical long elliptical shape depending on the tire inclination. In this invention, the area surrounded by the outer contour 19 is defined as the apparent ground contact area, and the ratio of the ground contact area of the blocks included within the same contour to this area is within ±0.05, that is, within a range of change of 0.10 or less at any camber angle. shall remain within. By determining the size, position and shape of the blocks with such considerations in mind, it is possible to smoothly increase the camber thrust generated in the tire when the camber angle is successively added. In this sense, it is more desirable that the area ratio is within ±0.03, that is, 0.06 or less. For tire A having the tread pattern shown in FIG. 1 of the present invention, as well as tire B and conventional tire C shown in FIG.
A driving test was conducted on a motocross course. The tire size was 5.10-18, and a 4-ply bias structure was used in common. The main specifications of the test tires are shown in Table 1.

[Table] Here, tire C is block row 1 in Figure 6.
Only blocks corresponding to 8'-1 are arranged on the circumference of the tire. Also, the block ground area/
The amount of change in the apparent ground contact area is shown as the maximum value minus the minimum value in the range of the camber angle from 0 to 40 degrees. The test results are shown in Table 2.

[Table] In Table 2, both tires A and B of the present invention were smooth when turning with the vehicle body tilted, but tire C could slip significantly at a certain tilt angle of the vehicle body, and the overall The amount of slippage was large and caused a sense of anxiety. This point is evident in lap time. Tires A and B had relatively little wear on the blocks after running, while Tire C had wear on the edge of the block on the side where the driving force and camber thrust were applied, despite using the same rubber type. The result of this edge wear is clearly visible in the latter lap times (average of 5 to 10 laps). As described above, according to the present invention, wear of a motocross tire can be advantageously reduced, and effective ground gripping performance can be maintained regardless of the progress of the wear.

[Brief explanation of the drawing]

FIG. 1 is a developed view of a tread pattern showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG.
FIG. 3 is a cross-sectional view taken along line B-B, FIG. 4 is taken along line C-C, and FIG. 5 is taken along line D-D.
FIGS. 7a, b, c, d and e are footprint diagrams showing changes in the ground contact shape as the camber angle increases. 2...Tread, 4...Bead part, 5...Carcass,
18-1, 18-2, 18'-1, 18'-2... Group of blocks.

Claims (1)

[Claims] 1 A pair of bead parts, a toroidal carcass extending between these bead parts, and a large number of horizontal grooves on the outer surface extending from the crown part of the carcass to both sides along the contour of the carcass. A tire having a tread consisting of a plurality of blocks separated from each other by at least three longitudinal grooves, the mutual center of adjacent blocks within a group of blocks lined up in the width direction of the tread being 3 to 25.
The mutual arrangement of the block groups includes step-shifted blocks shifted in the circumferential direction of the tread, and the longitudinal grooves between the blocks and the blocks between the longitudinal grooves overlap in the circumferential direction via the lateral grooves and are lined up in the width direction. The total length of the outer surface of the block measured by
%, the overall block distribution is within the range of ±0.05 in terms of the change in ground contact area/apparent ground contact area of the blocks according to the camber angle of the tire, and the main part of all blocks is on uneven ground. A first side surface on which the driving force acts when driving, a second side surface located on the opposite side of the first side surface, a third side surface on which the camber thrust of the tire also acts, and this third side surface. and a fourth side surface located on the opposite side of the side surface, so that the projected area of the side surface facing the direction in which the driving force and the camber thrust act, respectively, is the first than the second and the fourth than the fourth. A motocross tire for motorcycles characterized by having three blocks each having a large size. 2 The group of blocks containing blocks with different levels is at least 1/2 of all groups of blocks.
The tire according to claim 1, which occupies the following. 3. The tire according to claim 1, wherein all of the groups of blocks include differential blocks. 4. The tire according to claim 1, wherein the first side surface of the block faces the direction of the driving force and is substantially perpendicular to the direction of the driving force. 5. Claim 1, wherein the third side of the block faces the direction of the camber thrust and is substantially perpendicular to the direction of the camber thrust.
The tire according to item 1 or 4. 6 The first side is inclined with respect to the normal passing through the edge of the block erected on the outer surface of the block, and the second side is expanded toward the base by being inclined at a larger angle with respect to the same normal. Claim 1, 4, or 5 forming a block
Tires listed in section. 7 The third side is inclined with respect to the normal passing through the edge of the block erected on the outer surface of the block, and the fourth side is expanded toward the base by being inclined at a larger angle with respect to the same normal. A tire according to claim 1, 4, 5 or 6 forming a block. 8 Each block is 70 to 160 when expanded by 300%
A tire according to claim 1, comprising a treaded rubber having a modulus of Kg/cm ² and a shore A hardness of 55 to 75°. 9 Each block is 90 to 140 when expanded by 300%
A tire according to claim 1, comprising a treaded rubber having a modulus of Kg/cm ² and a shore A hardness of 38 to 65°.