JP4313115B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire capable of ensuring steering stability and ride comfort and reducing vehicle interior noise such as road noise.

  When the vehicle travels on a relatively rough road surface, noise called road noise is generated in the passenger compartment. This road noise is one of the noises related to tires. Road irregularities are input to the tire tread, causing the tires to vibrate, and this vibration follows the axle, suspension, vehicle body and propagation path, and finally the vehicle. Appears as room noise.

  As a method for reducing this road noise, there are mainly the purpose of increasing the rubber thickness of the tire tread part for the purpose of attenuating the tire vibration, reducing the rigidity of the tire side part, etc.When the rubber thickness of the tread rubber is increased, Tire mass will increase and fuel economy will deteriorate. If a technique for lowering the hardness of the tread rubber or a technique for lowering the rigidity of the tire side portion in order to ease the input from the road surface, the pattern rigidity of the tread is lowered, and the steering stability is lowered. Therefore, it has been difficult to achieve both road noise reduction and steering stability by changing the rubber composition and hardness of a single tread.

In order to solve this problem, as shown in Patent Document 1, a method has been proposed in which the tread portion is divided into three in the tire axial direction and rubbers having different hardness are used in the central region of the tread portion and the shoulder portions on both sides. ing. In this method, rubber having low hardness is used for a part of the tread portion, so that road noise and the like are reduced and a decrease in steering stability is suppressed.
JP 2001-10308 A (see paragraph 0006)

  However, the method shown in Patent Document 1 is not limited to maintaining steering stability, and is not sufficiently satisfactory in reducing road noise and riding comfort, and it is hoped that a pneumatic tire capable of satisfying these performances will appear. It is rare.

  In view of the above-described problems, an object of the present invention is to provide a pneumatic tire capable of ensuring steering stability and ride comfort and at the same time reducing interior noise such as road noise.

  In order to achieve the above object, the present inventor first made various studies focusing on reducing road noise. High-frequency road noise (250 Hz to 300 Hz) propagated as vehicle interior noise has a portion overlapping with tire cavity resonance, which causes vehicle interior noise. Tire cavity resonance can be avoided by shifting the vibration mode frequency or lowering the level.

  As a technique for this, the present invention uses FEM analysis, and the tread portion has a two-layer structure of a cap rubber layer on the tread surface side and a base rubber layer disposed on the inner side thereof. The base rubber layer in the center region passing through the tire equator plane is divided into a two-layer structure consisting of a base upper layer rubber and a base lower layer rubber. By changing the rubber hardness and rubber modulus, the longitudinal, lateral and longitudinal rigidity is increased. It has been found that it is possible to provide a pneumatic tire that can sufficiently reduce road noise and also satisfy steering stability and ride comfort without being changed.

  That is, in the pneumatic tire according to the present invention, the tread portion has a two-layer structure of a cap rubber layer on the tread surface side and a base rubber layer disposed inside thereof, and among the base rubber layers, It is characterized in that the rubber hardness and rubber modulus of the lower layer rubber in the center region through which the tire equatorial plane passes in the tire width direction are set higher than those of other parts.

  Specifically, the JIS A hardness of the other part of the base rubber layer is 55 to 75 and the modulus (M100 MPa) is 2 to 4, whereas the JIS A hardness of the lower layer rubber in the center region is 75 to 100, The modulus (M100 MPa) is set to 8-12.

  According to the above configuration, in the base rubber layer, by setting the rubber hardness and modulus of the lower rubber in the center region higher than other parts, it becomes possible to maintain steering stability and riding comfort and reduce road noise. . This is because the rate of increase of tire stiffness, road noise, etc. with respect to changes in rubber hardness and modulus in each region, that is, sensitivity is different. In the present invention, by utilizing these differences in sensitivity, it is possible to achieve both maintenance of steering stability and riding comfort and reduction of road noise and the like.

  The range of the center region is Wc / W, where W is the overall width from the tire equatorial plane to the end of the base rubber layer in the tire width direction and Wc is the width of the center region to the end of the base lower layer rubber. 0.3-0.8 are preferable and 0.4-0.6 are more preferable. If it is smaller than 0.3, the effect of shifting the tire vibration frequency from the high-frequency road noise (250 to 300 Hz) is small, and if it is larger than 0.8, the road noise reduction effect is great and the steering stability is improved. On the other hand, ride comfort deteriorates.

  In addition, the rubber thickness hc of the lower rubber layer in the center region is preferably 0.3 to 0.7, more preferably 0.4 to 0.6, with respect to the total thickness h of the base rubber layer. . If it is less than 0.3, the effect of reducing road noise associated with the change in rubber hardness and rubber modulus is small, and if it exceeds 0.7, the ride comfort is deteriorated.

  Such a base lower layer rubber can be easily formed by attaching a tape-like rubber to the back surface of the upper layer rubber constituting the base rubber layer.

  Furthermore, by setting the rubber hardness and rubber modulus of the cap rubber layer lower than those of the upper and lower rubber layers of the base rubber layer, road noise can be reduced and riding comfort can be maintained.

    As described above, according to the present invention, the tread portion has a two-layer structure of the cap rubber layer and the base rubber layer disposed inside thereof, and the tire equatorial plane in the tire width direction is the base rubber layer. The base lower layer rubber with respect to the width of the base lower layer rubber with respect to the entire width W of the base rubber layer and the entire thickness of the base rubber layer, with the rubber hardness and rubber modulus of the base lower layer rubber in the center region passing through being set higher than other portions By setting the thickness of the vehicle to a predetermined range, it is possible to maintain steering stability and riding comfort and reduce road noise.

    Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an essential part in the axial (width) direction of a radial tire among pneumatic tires showing an embodiment of the present invention, and illustrates from a tire equatorial plane A to a tread end on one side.

  The radial tire 1 has a pair of bead portions 2 and sidewall portions 3 extending radially outward from the bead portions, a tread portion 4 connecting the upper ends thereof, and both ends thereof are folded back by bead cores 5 along the inner periphery thereof. And a carcass 6 supported. Since the belt layer 7 is provided between the tread portion 4 and the carcass 6 and the reinforcing structure thereof is the same as that of a general radial tire, a detailed description thereof is omitted.

  The tread portion 4 has a cap-base structure composed of two layers of a cap rubber layer 10 and a base rubber layer 11 located inside thereof. A plurality of main grooves 12 extending linearly or zigzag in the tire circumferential direction are formed on the outer peripheral surface of the cap rubber layer 10, and are omitted in the illustrated sectional view. 12 are formed in the crossing direction of the groove 12, and in the tire circumferential direction, auxiliary grooves that connect the sub-grooves and the lateral grooves that are narrower than the main groove are formed to form a predetermined tread pattern.

  The cap rubber layer 10 is set to have lower rubber hardness and modulus than the upper and lower rubber layers 11a and 11b of the base rubber layer 11, thereby reducing road noise and maintaining riding comfort.

  On the other hand, the base rubber layer 11 is divided into a total of three regions, a center region X formed with the equator plane A as a center and a shoulder region Y formed on both sides thereof. The rubber hardness and rubber modulus of the lower layer rubber 11b are set higher than those of the other portions 11a. In the present embodiment, a tape-like rubber 11b having a high rubber hardness and modulus is affixed to the back side of the center region X in the base rubber layer 11, so that a two-layer structure is formed only in the center region X. The other region is a single base rubber 11a.

  Specifically, in the base rubber 11a of the other part 11a of the base rubber layer 11, the JIS A hardness is set to 55 to 75, and the modulus (M100 MPa) is set to 2 to 4. On the other hand, in the base lower layer rubber 11b in the center region X, the JIS A hardness is set to 75 to 100, preferably 90 to 100. Moreover, the modulus (M100 MPa) of the base lower layer rubber 11b in the center region X is set to 8 to 12, preferably 10 to 12.

  The rubber hardness is measured by durometer hardness according to JISK6253 type A. The rubber modulus is obtained from the tensile stress at 100% elongation in the dumbbell shape No. 3 according to JISK6251.

  Here, in the range of the center region X, the total width from the tire equatorial plane A to the end portion of the base rubber layer in the tire width direction is W, and the width to the end portion in the center region of the base lower layer rubber 11b is Wc. Wc / W is 0.3 to 0.8, and 0.4 to 0.6 is a more preferable range. When the value of Wc / W is smaller than 0.3, the effect of shifting the tire vibration frequency from the high frequency road noise (250 to 300 Hz) is small, and when the value of Wc / W is larger than 0.8, the road The noise reduction effect is great and the handling stability is improved, but the ride comfort is worsened.

  The rubber thickness hc of the base lower layer rubber 11b in the center region X is such that hc / h is 0.3 to 0.7, more preferably 0.4 to 0.6, where h is the total thickness of the base rubber layer 11. It is said. When hc / h is smaller than 0.3, the road noise reduction effect due to the change in rubber hardness and rubber modulus is small, and when it exceeds 0.7, the ride comfort is deteriorated.

  In such a structure of the base rubber layer 11, by setting the rubber hardness and the modulus of the center region lower layer rubber 11b higher than other parts, it is possible to maintain steering stability and riding comfort and reduce road noise. It becomes.

  Next, examples of the pneumatic tire having the above-described configuration will be described. Table 1 shows the results of evaluating nine types of radial tires and performing evaluation tests on road noise, steering stability, and riding comfort performance.

  In Examples 1 and 2, the cap rubber layer 10 uses a single rubber, the base rubber layer 11 is divided into three regions, and the rubber hardness and modulus of the base lower layer rubber 11b in the center region X are set within the scope of the present invention. Moreover, the width ratio Wc / W of the base lower layer rubber 11b and the thickness ratio hc / h of the base lower layer rubber 11b are radial tires set within the scope of the present invention. The base upper layer rubber in the center region X and the rubber in the shoulder region have the same rubber hardness and modulus because they are made of a single rubber, but are individually displayed for convenience.

  The comparative example 1 shows that the hardness (JISA hardness is 55) and the modulus of the lower layer rubber 11b in the center region X are below the lower limit value of the present invention. In Comparative Example 2, the width ratio (Wc / W = 1) of the lower layer rubber 11b is also outside the scope of the present invention, that is, in the base rubber layer 11, the lower layer rubber is formed over the entire width. Show. The comparative example 3 shows that the thickness ratio (hc / h = 0.2) of the lower layer rubber 11b is below the lower limit of the present invention. The comparative example 4 shows that the thickness ratio (hc / h = 0.9) of the lower layer rubber 11b exceeds the upper limit of the present invention.

  In Comparative Example 5, the base rubber layer 11 used a single rubber. Using this as a control, the road noise, steering stability, and riding comfort of each tire were evaluated. In Comparative Example 6, the hardness of the base lower layer rubber 11b (JISA hardness is 55) is lower than the lower limit of the present invention, and in Comparative Example 7, the modulus (2.0) of the base lower layer rubber 11b is the lower limit of the present invention. Less than

  The test tire used was a radial tire having a tire size of 235 / 45ZR17, and the test vehicle was a 3000cc FR vehicle. Steering stability and ride comfort are evaluated by panelists. It represents with the relative value at the time of setting the comparative example 5 as 100, and it shows that steering stability and riding comfort are excellent, so that a numerical value is high.

  For road noise, a tire noise test method based on JASO C 606-81 was adopted by a stand-alone table test in which a tire alone filled with an air pressure of 220 kPa was placed on a rotating drum. However, in the noise measurement, the partial average level of 235 Hz to 280 Hz of the transfer function of the tire wheel vertical downward when the vertical downward load is input to the tire center portion is set to 0 as Comparative Example 5, and the level difference [dB] It was evaluated by. A lower level (−) indicates that road noise is reduced.

  As shown in Table 1, in Examples 1 and 2 in which the base lower layer rubber 11b having a high hardness and modulus is disposed in the center region of the base rubber layer 11, the road noise is “−1.8” compared to Comparative Example 5. “−1.2”, and steering stability and ride comfort are also improved.

  On the other hand, in Comparative Example 1 in which the rubber hardness and modulus of the base lower layer rubber 11b are small, the riding comfort is good, but the steering stability is poor, and the road noise is high as “0.7”. . In Comparative Example 2 in which the base lower layer rubber 11b is formed over the entire width in the tire width direction, the steering stability is improved and road noise is reduced, but the ride comfort is deteriorated.

  In Comparative Example 3 in which the thickness ratio (hc / h = 0.2) of the base lower layer rubber 11b is lower than the lower limit of the present invention, the steering stability is lower than that in Comparative Example 5 in which the base rubber layer 11 is made of a single rubber. Better, but no change in ride comfort and road noise. In Comparative Example 4 in which the thickness ratio (hc / h = 0.9) of the base lower layer rubber 11b exceeds the upper limit of the present invention, steering stability is improved and node noise is reduced, but riding comfort is deteriorated. .

  Further, in Comparative Example 6 in which the rubber hardness of the base lower layer rubber 11b is small, the road noise is “−1.3” and the ride comfort is “113”, but the steering stability is poor. Further, in Comparative Example 7 in which the modulus of the base lower rubber 11b is small, the riding comfort is good, but the steering stability is poor and the road noise is high as “0.5”.

Sectional drawing of the principal part of the radial tire which shows embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radial tire 2 Bead part 3 Side wall part 4 Tread part 5 Bead core 6 Carcass 7 Belt layer 10 Cap rubber layer 11 Base rubber layer 11a Other parts 11b Lower layer rubber A Tire equatorial surface B Tread edge X Center area Y Shoulder area

Claims (3)

The tread portion has a two-layer structure of a cap rubber layer on the tread surface side and a base rubber layer disposed inside the tread portion, and the base rubber layer is vertically moved in a center region through which the tire equatorial plane passes in the tire width direction. is a two-layer structure, a pneumatic rubber hardness and rubber modulus of the base underlying rubber of the center region, characterized in that it is set to satisfy the following to other parts of the relationship between the base rubber layer tire.
<Width Wc of base lower layer rubber relative to overall width W of base rubber layer>
Wc / W = 0.3-0.8
<Thickness hc of base lower layer rubber relative to overall thickness h of base rubber layer>
hc / h = 0.3-0.7
<Rubber hardness JIS A>
Base lower layer rubber (75 to 100)> other part (55 to 75)
<Rubber modulus MPa>
Base lower layer rubber (8.0 to 12.0)> Other parts (2.0 to 4.0) 2. The pneumatic tire according to claim 1 , wherein the base lower layer rubber is formed by attaching a tape-like rubber to a back surface of an upper layer rubber constituting the base rubber layer. The pneumatic tire according to claim 1 or 2 wherein the rubber hardness and rubber modulus of the cap rubber layer, characterized in that it is set lower than the vertical one of the rubber layers of the base rubber layer.

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