JP4327553B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a studless tire for RV and other wide pneumatic tires, and more particularly, to a pneumatic tire in which a tread surface having a plurality of radii of curvature has been devised with respect to the geometric shape of the tread surface. .

  Conventionally, with respect to blocks formed between main grooves on the tread surface of a pneumatic tire, if the tread radius, which is the radius of curvature of the tread surface, is small, the contact pressure at the center of the block increases and the contact at the block end is insufficient. There was a point. If the ground contact pressure on the block surface becomes uneven, the running performance and wear resistance of the tire are adversely affected, and buckles are likely to occur on the tire surface. In order to solve such a problem, there has been proposed a pneumatic tire having a profile in which two types of tread radius are combined and each tread surface shape intersects at a specific angle (for example, Patent Documents). 1).

JP 2001-18615 A

  However, for example, when targeting RV flat size pneumatic tires such as 325 / 25R24, the ground contact width of the tires is wide, so that two large radiuses are bent to 4 to 14 degrees as in the background art above. Even if the adopted profile is used, the buckle cannot be prevented. On the other hand, if a small radius is used and a bent profile is used, the ground contact pressure in the block surface cannot be made uniform as in the conventional case. Further, if such a profile is bent from 4 degrees to 14 degrees, it is difficult to secure a ground contact area of the shoulder portion.

  Therefore, the present invention has been made in view of the above, and an object of the present invention is to provide a pneumatic tire having a profile capable of optimizing the contact shape and contact pressure distribution even in a wide RV size.

  In order to achieve the above-described object, the pneumatic tire according to claim 1 has two or more tread radius on one side when the profile on one side is divided into two on the equator plane, and two or more on the tread surface on the one side. In the pneumatic tire having an equatorial plane symmetrical pattern in which the circumferential main grooves are engraved, between the equator plane and the innermost circumferential main groove, between the circumferential main grooves, and the outermost circumferential groove. Each of the profiles from the shoulder portion to the tread grounding end of the shoulder portion is formed by an arc, and an inflection point on the profile generated by the intersection of the adjacent arcs is present in the circumferential main groove. All the acute side crossing angles between the arcs at the points are 1 degree or more and 3 degrees or less.

  The pneumatic tire of the equatorial plane target pattern means a pneumatic tire having a symmetrical profile and a tread pattern with respect to the equator plane. For this reason, the profile on one side when divided into two on the equator plane also applies to the profile on the opposite side. Therefore, in the present invention, the characteristics of the entire pneumatic tire are characterized by clarifying the profile of the one side and the tread surface.

  The present invention is applicable to a relatively wide tire in which two or more circumferential main grooves are cut on the tread surface on one side. For example, when there are three circumferential main grooves on one tread surface, there are four tread upper blocks on the one side. These blocks are circumferential main grooves from the most equatorial plane, that is, between the inner circumferential main groove and the equatorial plane, between each of the plurality of circumferential main grooves, and from the most shoulder side circumferential main groove. That is, it is constituted by a block from the outermost circumferential main groove to the tread grounding end of the shoulder portion.

  The profile of the block is formed by connecting arcs. And the inflection point of the circular arc connected is designed so that it may be arrange | positioned in a circumferential direction main groove, and an inflection point does not appear on a tread block. Therefore, the cross-sectional curve of the block is a smooth arc curve. Further, the arcs to be connected have different center positions, and the connection is a cross connection. By setting the acute angle of the crossing angles to 1 degree or more and 3 degrees or less, it is possible to provide a profile in which the contact pressure is uniform throughout the entire tire width even for a wide range of tires.

  The pneumatic tire according to claim 2 is the pneumatic tire according to claim 1, wherein, among the adjacent arcs, the radius of curvature of the arc positioned on the outer side in the width direction is positioned on the inner side. The radius of curvature of the arc is equal to or greater than the radius, and the size of the acute angle crossing angle on the outer side in the width direction among the acute angle crossing angles in adjacent circumferential grooves is equal to or greater than the acute angle crossing angle on the inner side.

  In the present invention, of the radii of curvature of adjacent arcs on the profile, those located on the outer side in the width direction have the same size or larger than those located on the inner side. Therefore, the radius of curvature does not decrease in the profile from the equator plane position to the tread ground contact edge. Therefore, uneven contact pressure due to a small curvature radius even near the shoulder is prevented. In addition, there are as many acute angle crossing angles between adjacent arcs as there are circumferential main grooves. It is possible to prevent uneven contact pressure and provide an optimal profile for a wide range of tires.

  The pneumatic tire according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the circumferential main groove is chamfered with an arc at the opening to the tread surface. It is a thing.

  If the profile is configured by connecting a plurality of arcs, the tendency of the circumferential main groove portion to deform in the direction in which the frontage becomes narrower tends to appear. Therefore, the opening size of the main groove is maintained by chamfering the opening to the tread surface of the main groove with an arc. As a result, it is possible to prevent deterioration of the grip and drainage of the main groove on snow. In addition, since the edge of the main groove can be effectively used, it is effective in improving the skid performance without degrading other performances.

  The pneumatic tire according to the present invention can increase the ground contact area of the tread surface by geometrically devising the tread profile so that the ground contact area of the shoulder portion can be increased even in a studless tire for RV or other wide size tires. Can do. Further, the contact pressure of the entire tire can be made uniform, the buckle of the center portion can be prevented, and uneven wear resistance, braking on ice, and skid on snow can be improved.

  Below, the example of the pneumatic tire concerning the present invention is described in detail based on a drawing. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. The figure shows a meridional section when the pneumatic tire 1 mounted on a regular rim and filled with air is cut in the radial direction, and shows one side when the pneumatic tire 1 is divided into two at the equator plane 2. This pneumatic tire 1 is of a type having three circumferential main grooves 3, 4 and 5 on one side, and therefore six on the entire tire surface, and has a symmetrical pattern with the equator plane 2 as a boundary.

  The profile which is the cross-sectional contour of the tire is determined by the block shape between the main grooves and the shape of the block between the main groove 5 on the most shoulder side and the tread ground contact end 6. Therefore, in the example shown here, the pneumatic tire 1 is a symmetric type, so the profile of the entire tire is specified by the cross-sectional shapes of the four blocks 7, 8, 9, and 10. In general, in a tire having N main grooves on one side, there are 2N + 1 blocks in the entire tire width, and in a symmetrical type, the profile of the entire tire is determined by the profile of N + 1 blocks on one side. It will be.

  Here, the distance between the center positions of the circumferential main grooves with respect to the tire contact width is within ± 30% of the contact width / (N + 1) where N is the number of the circumferential main grooves on one side. This is because if the contact width in the tire width direction is too small, the block rigidity in the contact surface becomes non-uniform and uneven wear occurs.

  The profile of each block 7, 8, 9, 10 is formed by a circular arc and has respective curvature radii TR1, TR2, TR3, TR4. When the tire profile is formed by a series of arcs, the center points of the arcs usually do not coincide. If the radii of curvature do not coincide with each other, the end of the arc intersects the other arc. In the present invention, the intersecting points of the arcs are made to coincide with the positions of the circumferential main grooves 3, 4, and 5. Therefore, the inflection point that occurs when crossing exists theoretically only as in the design, and does not appear on the actual profile. In the present invention, the theoretical intersection angles at the inflection points that intersect are all set to 1 degree or more and 3 degrees or less.

  The intersection angle is an angle when the arc profiles adjacent to each other literally intersect. The crossing angle in this case refers to the angle that is the acute angle of the acute angle and the obtuse angle. In the figure, the angle of deviation when the normal is extended from the end point of each arc intersecting in the same main groove is the intersection angle. That is, the intersection angle of the arc of block 7 and the arc of block 8 is θ1, the intersection angle of the arc of block 8 and the arc of block 9 is θ2, and the intersection angle of the arc of block 9 and the arc of block 10 is θ3. It will be.

  When θ1, θ2, and θ3 are set to angles of 1 degree or more and 3 degrees or less, the contact area can be optimized and the contact pressure can be made uniform even with a wide tire, thereby preventing buckling and on the ice. It is possible to improve braking performance and uneven wear resistance. In particular, a studless tire for RV can secure a sufficient contact area without impairing the snow grip and snow skid resistance, and contributes to safe driving in icy and snowy areas.

  Moreover, in this invention, it is set as the relationship from which the magnitude | size of the curvature radius of the circular arc located in the width direction outer side becomes more than the curvature radius of the said circular arc located inside among the said adjacent circular arcs about said TR1-4. In addition, with respect to θ1 to 3, the magnitude of the acute angle crossing angle on the outer side in the width direction among the acute angle crossing angles in the adjacent circumferential grooves is not less than the acute angle crossing angle on the inner side. Expressing the above relationship by an expression, TR1 <TR2, TR2 <TR3, TR3 <TR4, and θ1 ≦ θ2 ≦ θ3.

  This prevents uneven contact pressure due to the small curvature radius even near the shoulder. In addition, there are as many acute angle crossing angles between adjacent arcs as there are circumferential main grooves. Non-uniform contact pressure is prevented, and an optimal profile can be provided for a wide range of tires. If the contact pressure is uniform and the contact area is increased, uneven wear resistance and braking performance can be improved. If it is a studless tire for RV, braking performance on ice and braking performance will be improved.

  Further, in the circumferential main grooves 3, 4, 5, the openings 11, 12, 13 to the tread surface are chamfered with arcs. When the profile is configured by connecting a plurality of arcs, the tendency of the circumferential main groove portion to deform in the direction in which the frontage becomes narrower appears. Therefore, by chamfering the opening to the tread surface of the main groove with an arc, the opening size of the main groove can be maintained, and deterioration of the on-snow grip and drainage of the main groove can be prevented. In addition, if the cross-sectional shape of the groove bottom parts 14, 15, and 16 of the circumferential main grooves 3, 4, and 5 is a shape that opens to the outside of the tire such as a rectangle or a V shape, it may be configured by a straight line. However, it may be configured by a curve or an arc. The width of the main groove is preferably 3 mm to 10 mm and the depth is preferably 8 mm to 13 mm.

  Table 1 shows the experimental results showing the curvature radius and acute crossing angle of the profile and the effect. In the table, TR1-4, θ1-3 are profile curvature radii and acute crossing angles corresponding to FIG.

  The braking performance on ice was measured by installing a 255 / 55R18 size tire in a standard rim and setting it to a standard air pressure of 200 kPa, and mounting it on a 3.5-liter passenger car. Specifically, on the icy road test course, the braking distance when ABS braking was performed from a traveling state at a speed of 40 km / h was measured five times, and the average braking distance of three times excluding the maximum value and the minimum value was obtained. The values in the table are shown by an index in which the reciprocal of this average braking distance is obtained and the value of the conventional tire is 100. Therefore, the larger this value, the better the braking performance on ice.

  The skid skid was evaluated by a sensory test of an experienced paneler when the test tire was mounted on the vehicle and the vehicle ran on snow. The number of skilled panelists was 3, and the maximum speed at which skidding did not occur was obtained as an average value of 3 persons, and this was expressed as an index with the conventional tire as 100. It can be said that the larger the value, the better the skidability on snow.

  The uneven wear resistance is the same as the amount of wear in the center area of the tire tread surface (tread surface) after the test tire is mounted on the vehicle and the test course consisting of a dry paved road is run for 8000 km at an average speed of 35 km / h. The amount of wear in the shoulder region was measured and evaluated. Specifically, the reciprocal of the difference in wear amount between the two was obtained and evaluated. Since the measurement results are expressed as an index with the conventional tire as 100, it can be said that the larger the numerical value, the better the uneven wear resistance.

  When the acute crossing angle θn (n = 1, 2, 3) is made to satisfy the relationship of 1 ≦ θn ≦ 3 (deg), the braking performance on ice and the uneven wear resistance are improved as compared with the conventional case (conventional example). Experimental examples 1, 2). This is not related to whether the curvature radii TR1 to 4 are increasing toward the outer side in the width direction or decreasing. This is clear compared with the case where the above formula is not satisfied (Comparative Examples 1 and 2). Further, when TR1 to TR4 are further made to satisfy the relationship of TR (n) ≦ TR (n + 1) (n = 1, 2, 3), the braking performance on ice is further improved (conventional example, experimental example 3). The same is true if n is 4 or more as in the case where there are four or more circumferential main grooves on one side.

  In addition, when the opening of the circumferential main groove is chamfered, the crushing of the main groove is suppressed, and drainage and grip force reduction can be prevented. Thereby, braking performance on ice and uneven wear resistance, in particular, skidding on snow can be improved.

  This invention is an invention derived from experience and scrutiny and the inventor's high creativity, and the tire profile can derive the optimum shape only with a simple geometric design from the viewpoint of its various performances. is not. For example, simply increasing the number of inflection points just because the width is widened, and setting the crossing angle to 4 degrees to 14 degrees as in the conventional case, the drop amount of the profile itself becomes too large, and the ground contact area is reduced. It cannot be secured. Therefore, the present invention is excellent for a wide tire from the viewpoint of improving the braking performance, the skid performance, and the uneven wear resistance.

  As described above, the pneumatic tire according to the present invention is a large index concept for determining the profile of a wide type pneumatic tire, and thus the contact pressure of the tire can actually be made uniform over the entire width.

It is sectional drawing which shows the pneumatic tire which concerns on Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Equatorial plane 3, 4, 5 Circumferential main groove 6 Tread grounding edge 7, 8, 9, 10 Block 11, 12, 13 Opening 14, 15, 16 Groove bottom part TR1, TR2, TR3, TR4 Curvature Radius θn Acute crossing angle

Claims (3)

In a pneumatic tire having an equatorial plane symmetric pattern in which a profile on one side is composed of three or more tread radii when divided into two on the equator plane, and two or more circumferential main grooves are engraved on the tread surface on one side.
Profiles from the equator plane to the innermost circumferential main groove, between the circumferential main grooves, and from the outermost circumferential groove to the tread grounding end of the shoulder portion are each formed by an arc. And
An inflection point on a profile generated by the adjacent arcs intersecting is provided in the circumferential main groove, and the acute angle crossing angles between the arcs at the inflection points are all 1 degree or more and 3 degrees or less. A pneumatic tire characterized by being.   Of the adjacent arcs, the radius of curvature of the arc positioned on the outer side in the width direction is equal to or larger than the radius of curvature of the arc positioned on the inner side, and the outer side in the width direction of the acute crossing angle in the adjacent circumferential groove. 2. The pneumatic tire according to claim 1, wherein a magnitude of the acute angle crossing angle is greater than or equal to the acute angle crossing angle on the inner side.   The pneumatic tire according to claim 1 or 2, wherein the circumferential main groove has an opening to the tread surface chamfered with an arc.

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