JP5503457B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire with improved handling stability during turning by improving a tread profile.

  Conventionally, as a tread profile that is an outer surface contour line of a tread portion of a pneumatic tire, a so-called multiradial tread (hereinafter sometimes simply referred to as “MRT”) in which a plurality of arcs having different radii of curvature are smoothly connected is known. ing. FIG. 4 shows an example of such an MRT tread profile TP.

  As shown in FIG. 4, the MRT tread profile TP generally employs an arc having a smaller radius of curvature Rai (i = 1, 2,...) Toward the outer side in the tire axial direction. As a result, the camber amount Y, which is the tire radial direction distance between the tire axial line X passing through the position of the tire equator C and the tread profile TP, is small on the tire equator side and increases as it approaches the ground contact Te.

  Accordingly, an arc curve having a relatively large radius of curvature is formed near the tire equator of the tread portion that is in contact with the road surface when traveling straight ahead, and the contact pressure is likely to be uniform. Thereby, a large grip is obtained when going straight, and straight running stability is ensured.

  On the other hand, in the tread profile TP of the MRT, in order to smoothly connect the tread portion and the sidewall portion, the radius of curvature rapidly decreases in the vicinity of the middle region that separates 30% of the tread contact width TW from the tire equator C. Tend. However, since this middle region is a region that receives a large load in contact with the road surface at the time of turning, if the curvature radius of the middle region becomes small, the contact pressure at this part becomes non-uniform at the time of turning, and a stable side grip is obtained. May not be obtained.

  Various studies have been made to improve the steering stability during turning. Related technologies include the following.

Japanese Patent Laid-Open No. 05-016608

  The present invention has been devised in view of the above problems, and in the tread profile at the tire meridional section, the middle section, which is the main contact area at the time of turning, is basically formed in a straight line. The main purpose is to provide a pneumatic tire that improves the steering stability of the vehicle.

  The invention according to claim 1 of the present invention is a pneumatic tire having a tread portion, and is a tire meridian including a tire rotating shaft in a normal state in which a normal rim is mounted and a normal internal pressure is filled with no load. The profile of the tread portion in the cross section is as follows: a first point P1 on the outer surface of the tread that is separated from the tire equator C by a distance of 30 ± 2.5% of the tread ground contact width TW; The middle section to the second point P2 on the outer surface of the tread that is separated by a distance of ± 2.5% is formed by a straight line.

  According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, the crown section from the tire equator C to the first point P1 is a first arc curve.

  The invention according to claim 3 is the pneumatic tire according to claim 2, wherein the first arc curve is formed by connecting a plurality of arcs whose curvature radius decreases toward the outer side in the tire axial direction.

  According to a fourth aspect of the present invention, in the pneumatic tire according to any one of the first to third aspects, the tread profile includes a second arc curve in a shoulder section from the second point P2 to at least the ground contact end. It is.

  The invention according to claim 5 is the pneumatic tire according to claim 4, wherein the second arc curve is formed by connecting a plurality of arcs whose curvature radius decreases toward the outer side in the tire axial direction.

  Here, the tread contact width TW is a distance in the tire axial direction between the contact ends when a normal load is applied to the tire in the normal state and contacted to a plane with a camber angle of 0 degree. Further, the dimensions and the like of each part of the tire are values in the normal state unless otherwise specified.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA, “Design Rim” for TRA. "Or, if ETRTO, means" Measuring Rim ".

  The “regular internal pressure” is the air pressure defined by the standard for each tire. The maximum air pressure described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is the maximum air pressure for JATMA and TRA for TRA. If the value is ETRTO, it means “INFLATION PRESSURE”, but in the case of passenger car tires, it is 180 kPa.

  Furthermore, “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. “Maximum load capacity” for JATMA, “TIRE” for TRA The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is “LOAD CAPACITY” in the case of ETRTO.

  The tread profile of the pneumatic tire according to the present invention has a tread profile width TW from the tire equator C from a first point P1 on the outer surface of the tread that is separated from the tire equator C by a distance of 30 ± 2.5% of the tread contact width TW. A middle section to the second point P2 on the outer surface of the tread that is separated by a distance of 40 ± 2.5% is formed by a straight line. As a result, the ground contact pressure at the time of turning is made uniform, and a large ground contact area is ensured. Therefore, steering stability is improved.

It is sectional drawing of the right half which shows the pneumatic tire of one Embodiment of this invention. It is a figure which shows a tread profile. (A) is a comparative example, (b) is a tread profile of an example. It is a diagram which shows the tread profile of the conventional MRT.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire 1 of the present embodiment includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both sides thereof, and tire radial directions of the respective sidewall portions 3. It has a bead portion 4 that is located at the inner end and is attached to the regular rim J, and in this embodiment, one for a passenger car is shown.

  The pneumatic tire 1 includes a toroidal carcass 6 and a belt layer 7 disposed on the outer side in the tire radial direction of the carcass 6 and inside the tread portion 2.

  The carcass 6 includes a main body portion 6a straddling a pair of bead cores 5 and 5 in a toroidal manner, and a folded portion 6b that is continuous from both sides of the main body portion 6a and is folded around from the inner side in the tire axial direction around the bead core 5. And at least one carcass ply 6A. In the carcass ply 6A, carcass cords made of, for example, organic fibers are arranged at an angle of, for example, 75 to 90 ° with respect to the tire equator C direction.

  The belt layer 7 is formed by inclining steel cords at an angle of, for example, 15 to 45 ° with respect to the tire equator C. Outer two belt plies 7A and 7B are arranged so that the steel cords cross each other. Overlaid and configured. Further, the belt layer 7 is disposed over substantially the entire width of the tread portion 2 to ensure necessary tread rigidity.

  FIG. 2 shows a tread profile TP (contour shape of the outer surface 2A of the tread portion 2) on the tire meridional section including the tire rotation shaft in the normal state in which the normal rim J is mounted and the normal internal pressure is filled and in the no-load normal state. It is. In the tread profile TP, a region between the ground contact ends Te and Te is divided into a crown section Cr, a middle section Md, and a shoulder section Sh.

  The crown section Cr is a section from the tire equator C to a first point P1 on the outer surface 2A of the tread that separates a distance L1 of 30 ± 2.5% of the tread contact width TW. This crown section Cr is an area that is in contact with the road surface mainly when traveling straight ahead. In the present embodiment, this crown section Cr is formed from the first circular arc curve K1.

  The first arc curve K1 is a smooth curve that protrudes outward in the tire radial direction, and in the present embodiment, a plurality of arcs with decreasing curvature radii toward the outer side in the tire axial direction are connected in accordance with MRT. Is formed. In FIG. 2, a typical radius of curvature R1 is depicted. The number of arcs constituting the first arc curve K1 is not particularly limited as long as it is 2 or more, but preferably 3 or more, more preferably 4 or more.

  Further, it is desirable that the radius of curvature of the first circular arc curve K1 is set within a range of about 3 to 7 times the tread ground contact width TW. As a result, the ground contact pressure during straight traveling can be made uniform and the occurrence of uneven wear such as crown wear can be suppressed. Note that the first circular arc curve K1 may have a continuously changing curvature radius.

  The middle section Md is a section from the first point P1 to the second point P2 on the tread outer surface 2A that is separated from the tire equator C by a distance L2 of 40 ± 2.5% of the tread ground contact width TW. In the pneumatic tire of the present invention, the middle section Md is formed by a straight line L. The straight line L is smoothly connected to the crown section Cr without forming an inflection point. That is, in the present embodiment, the straight line L forms a tangent line at the first point P1 of the first circular arc curve of the crown section Cr.

  Thus, by forming the middle section Md of the tread profile TP as a straight line L and connecting it smoothly to the crown section, the contact pressure is made uniform and the contact area is reduced as compared with the case where it is formed by a conventional arc. Can be expanded. Therefore, a large and stable grip can be obtained during turning traveling where a large load is likely to act on the middle section Md, and steering stability is improved. In addition, it is possible to suppress an increase in the contact pressure at the connecting portion between the crown section Cr and the middle section Md, and to suppress uneven wear starting from this position.

  The reason why the middle section Md formed by the straight line L is limited to the above-described range is that this section receives the largest load during turning and affects the grip. In the crown section Cr, since the radius of curvature R1 of the tread profile TP is formed to be large as it is, the ground contact area necessary for improving the steering stability and the ground contact pressure are already made uniform. For this reason, in the vicinity of the tire equator C, even if the tread profile TP is straight, not only a sufficient effect cannot be expected, but there is a possibility of causing uneven wear, which is not preferable.

  The shoulder section Sh is a section on the outer side in the tire axial direction from the second point P2. This section is preferably formed by a second arc curve K2 in order to smoothly connect the middle section Md and the sidewall portion 3. The second arc curve K2 is not particularly limited as long as the second arc curve K2 is a curve that protrudes outward in the tire radial direction, but preferably, a plurality of curvature radiuses decrease toward the outer side in the tire axial direction in accordance with conventional MRT. It is desirable that these arcs are connected together. In FIG. 2, a typical radius of curvature R2 is depicted.

  In the present embodiment, the maximum curvature radius of the shoulder section Sh is formed smaller than the minimum curvature radius of the crown section Cr. More preferably, the radius of curvature of the arc of the shoulder section Sh is set within a range of 0.1 to 0.2 times the tread contact width TW.

  Furthermore, the straight line L forming the middle section Md is smoothly connected to the shoulder section Sh without forming an inflection point. That is, in the present embodiment, the straight line L forms a tangent line at the second point P2 of the second circular arc curve of the shoulder section Sh. Therefore, a local increase in the contact pressure can be suppressed even at the connection portion between the shoulder section Sh and the middle section Md, and uneven wear starting from this position can be suppressed.

  Furthermore, in the tread profile TP of the present embodiment, the camber amount Y is formed so as to gradually increase from the tire equator C toward the outer side in the tire axial direction. That is, the camber amount at the second point P2 is larger than the camber amount at the first point P1. This is not only useful for suppressing uneven wear, but is also desirable in that the ground contact width is gradually increased as the load increases, and smooth running transient characteristics are exhibited.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the illustrated embodiments, and can be implemented in various forms.

  A pneumatic tire for a passenger car of size 255 / 40R20 having the tread profile of FIG. 4 was prototyped based on the specifications shown in Table 1 and tested for steering stability and the like. The inner structure of the tire and the tread rubber were both the same, and the outer surface of the tread portion was a plain tread without a drainage groove. Each specification is as follows. In Comparative Example 1, the tread ground contact width TW is adjusted to 240 mm, and the camber amount at the ground end Te is adjusted to 12 mm.

<Comparative Example: FIG. 3 (a)>
This is a conventional MRT tread profile, and the radius of curvature of each section is formed as follows.
・ Crown interval Number of arcs 3
Arc radius of curvature (in order from the inside) 1200mm, 1000mm, 750mm
-Middle section Number of arcs 1
Arc radius of curvature 400mm
・ Shoulder section (from P2 to Te)
Number of arcs 2
Arc radius of curvature (in order from the inside) 100mm, 50mm

<Example: FIG. 3B>
・ Crown section Number of arcs 2
Arc radius of curvature (from inside) 1200mm, 1000mm
・ Middle section Straight line ・ Shoulder section (from P2 to Te)
Number of arcs 1
Arc radius of curvature 35mm
The test method is as follows.

<Steering stability>
The cornering power was determined from the cornering force measured using an indoor tester, and compared by an index with a comparative example of 100. The larger the value, the higher the cornering power and the better the steering stability. The cornering power was obtained by dividing by 2 the value obtained by subtracting the cornering force value CF (-1 °) at the slip angle -1 ° from the cornering force value CF (+ 1 °) at the slip angle + 1 °. As a cornering force per 1 ° of slip angle expressed by the following equation:
{CF (+ 1 °) -CF (-1 °)} / 2
CF (+ 1 °) and CF (-1 °) take into account the signs of plus and minus, respectively.

<Straight running stability>
After assembling a sample tire on a 9.0 rim rim at an internal pressure of 180 kPa, mounting it on four wheels of a 3000cc rear-wheel drive vehicle, only the driver gets on the dry asphalt road surface and wet asphalt road surface of the tire test course respectively. The car was run and the straight running stability, such as the presence or absence of wobbling, was evaluated by a five-point method based on sensory evaluation of the driver. The larger the value, the better the straight running stability.

<Abrasion resistance>
The test course was run for a total of 3000 km under the same vehicle conditions as above, and the state of wear on the outer surface of the tread portion was observed with the naked eye.
The test results are shown in Table 1.

  As a result of the test, it can be confirmed that the steering stability of the example is improved as compared with the comparative example.

  Next, the same experiment was performed on the example product by changing the range of the middle section forming a straight line. Also in this case, the camber amount at the ground contact end of the tread portion is constant. In addition, the crown section and the middle section are based on the arc curve of Comparative Example 1, but in each section, the arc connected to the straight line portion is smoothly connected to the straight line portion by adjusting the curvature radius. Table 2 shows the test results.

  As a result of the test, it can be confirmed that the result of the example is better than that of the comparative example.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 2A Tread outer surface C Tire equator J Rim K1 1st circular arc curve K2 2nd circular arc curve Cr Crown section Md Middle section Sh Shoulder section Te Grounding end TP Tread profile TW Tread ground width

Claims (5)

A pneumatic tire with a tread,
The profile of the tread portion at the tire meridional section including the tire rotation shaft in a normal state in which the tire is mounted in the normal rim and filled with the normal internal pressure is 30 ± 2.5 from the tire equator C to the tread contact width TW. The middle section from the first point P1 on the outer surface of the tread that is separated by a distance from the tire equator C to the second point P2 on the outer surface of the tread that is separated by 40 ± 2.5% of the tread ground contact width TW, A pneumatic tire characterized by comprising a straight line.   2. The pneumatic tire according to claim 1, wherein the tread profile includes a first arc curve in a crown section from the tire equator C to the first point P <b> 1.   The pneumatic tire according to claim 2, wherein the first circular arc curve is formed by connecting a plurality of circular arcs whose curvature radius decreases toward the outer side in the tire axial direction.   4. The pneumatic tire according to claim 1, wherein the tread profile includes a second arcuate curve in a shoulder section from the second point P <b> 2 to at least a ground contact end. 5.   5. The pneumatic tire according to claim 4, wherein the second arc curve is formed by connecting a plurality of arcs whose curvature radius decreases toward the outer side in the tire axial direction.

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