JPH02109705A - Pneumatic tyre - Google Patents

Abstract

PURPOSE:To reduce the thickness unevenness of a tread gum layer so as to improve a comfortableness during ride, and the like by enlarging a groove wall angle in the type tread surface normal direction of a sub-groove for forming a unit pitch in response top the magnitude of a groove area rate per one pitch. CONSTITUTION:A pneumatic tyre has a tread pattern consisting of blocks different in their pitches in a circumferential direction. In this case, as the groove area rate per one pitch on the tread surface increases, a groove wall angle thetain the tyre tread surface normal direction of a sub-groove 2 for forming the pitch increases. In other words, the groove angle thetaa of the sub-groove 2 at the unit pitch which larger groove area rate is made larger than the groove angle thetab of the sub-groove 2 at the unit pitch with smaller grove area rate. Thus, the difference between the unit pitch groove volume rate with the largest groove area rate in the tyre circumferential direction and the unit pitch groove volume rate with the smallest groove area rate in the same direction is set below 2%.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a tire with excellent uniformity in the circumferential direction, in particular, with small thickness unevenness of the tread rubber layer, vibration during running is reduced, and ride comfort is improved. Related to pneumatic tires with improved performance.

[Conventional technology]

Conventional pneumatic tires having a block pattern generally reduce noise during running, such as pattern noise, by varying the pitch in the tire circumferential direction. However, as shown in FIG. 2, the pitch P I+ P in the tire circumferential direction (- mark)
t+P:l+P4. ......When Pn (one pitch is represented by the sum of the lengths of blocks 4 and sub-grooves 2 in the tire circumferential direction) changes, the groove area ratio at each pitch, and eventually the groove volume ratio changes. Therefore, the thickness t of the rubber layer from the tread surface to the belt layer 3 varies along the tire circumferential direction. For example, in the case of FIG. 2, the thickness t4 of the tread rubber layer at P4, where the pitch is small, is 1. If such a tire is mounted on a vehicle and the vehicle is driven, the vehicle may vibrate and the ride comfort may be deteriorated.

This variation in the thickness of the tread rubber layer in the tire circumferential direction can be reduced by making the groove area ratio between each pitch the same. Due to the above constraints, it has been difficult to make the groove area ratio the same for all tread patterns.

[Problem to be solved by the invention]

An object of the present invention is to provide a pneumatic tire that reduces the variation in the thickness of the tread rubber layer in the tire circumferential direction of a tire having a conventional block pattern, improves ride comfort, and does not impair the appearance. be.

[Means to solve the problem]

An object of the present invention is to vary the pitch in the tire circumferential direction and to adjust the groove wall angle in the normal direction of the tire tread surface of the sub-grooves constituting the unit pitch according to the size of the groove area ratio per pitch. The difference ΔθΔθ between the groove wall angle θwax and the groove wall angle θmin in the normal direction of the tire tread surface of the sub-groove, which preferably form the maximum unit pitch and the minimum unit pitch of the groove area ratio, respectively ΔθΔθ=(θm
This can be achieved by setting ax-θwin) to at least 5°.

Hereinafter, the present invention will be specifically explained based on the drawings.

FIG. 1(A) is a circumferential cross-sectional view of a tire of the present invention at a unit pitch with a small groove area ratio, and FIG. 1(B) is a circumferential cross-sectional view of a tire with a unit pitch having a large groove area ratio.

The tire of the present invention.

The larger the groove area ratio per pitch on the tire tread surface, the larger the groove wall angle θ in the normal direction to the tire tread surface of the sub-grooves 2 constituting the pitch, that is, as shown in the figure, the groove area ratio is large. Groove angle θ of sub-groove 2 of unit pitch
The characteristic is that a (Fig. 1 opening) is made larger than the groove angle θb (Fig. 1 A) of the unit pitch sub-groove 2 with a small groove area ratio, thereby increasing the groove area ratio in the tire circumferential direction. is the groove volume ratio of the maximum unit pitch V III
The difference between IIX and the groove volume ratio V sin of the unit pitch with the smallest groove area ratio in the tire circumferential direction, ΔV1 ΔV "" Vaax Vfiin, is set to 2% or less, and the thickness t of the tread rubber layer in the tire circumferential direction is uniform. , the thickness t of this tread rubber layer
This prevents vibrations in the tires (vehicles) caused by uneven tires and improves ride comfort.

In the present invention, the unit pitch refers to a repeating unit of a block pattern in the tire circumferential direction, and as shown in FIG. (or the sum of the distances between one sub-groove and one block in contact with this sub-groove in the circumferential direction of the tire).

Further, the above-mentioned groove volume ratio V per unit pitch refers to a value defined by the following formula.

Groove volume ratio V = 100 This is a value expressed as a percentage (%) of volume.

In order to reduce the variation in the thickness of the tread rubber layer in the tire circumferential direction of the tire of the present invention, the groove volume ratio of the unit pitch where the groove area ratio in the tire circumferential direction is the largest is Groove volume ratio of unit pitch V m i
It is desirable that the difference Δ■ from n, that is, ΔV=(V, □−V+5tn), be 2% or less.

Then, the groove volume ratio of the unit pitch where the groove area ratio is the largest is 1. In order to keep the difference Δ■ between the groove volume ratio Vain of the minimum unit pitch and the groove volume ratio Vain to 2% or less, the groove wall angle θmax and the groove wall angle θl1in in the normal direction of the tire tread surface of the sub-grooves forming each unit pitch are It is necessary to set the difference Δθ Δθ−(θmax −8m1n) to at least 56.

As a means for manufacturing such a tire of the present invention, for example, the groove wall angle θ of the sub-groove constituting the unit pitch in the normal direction of the tire tread surface is increased in accordance with the size of the groove area ratio per unit pitch. Then, adjust the inclination angle of the wall surface of the sub-groove forming part (projection part) of the corresponding tire molding die. In other words, the size of the groove forming part (wall surface angle of the groove forming part) of the tread of the tire molding mold is adjusted so that the groove volume ratio per pitch is as close to the same as possible, and the tread rubber is adjusted by the cough mold during molding. It can be manufactured by preventing non-uniformity of layer thickness.

Hereinafter, the present invention will be specifically explained using examples and conventional examples.

The uniformity in the tire circumferential direction was evaluated using the RFV value specified in JASOC607.

Example, Conventional Example The tire pattern shown in Fig. 4 is used, and the tire circumferential direction is 180 mm.
/70R1385S, the groove depth of the minor groove is 8.0 mm, \θmax % θmin SAmax % Am1
n% Vmax, Vmin, tmax,,
tn+in and Δt are as shown in the table2
Five tires of each type were made.

The RFV of these two types of tires was measured, and the average value and an actual vehicle feeling ride test were conducted using a vehicle body equipped with four of each of the above tires on the front and front wheels, and the results are shown in the table.

(The following is a blank space) From the table, it can be seen that the example tire has a smaller RFV value than the conventional example tire because the uneven thickness of the tread layer has been reduced and the uniformity in the tire circumferential direction has been improved. It was confirmed that the comfort was improved.

〔Effect of the invention〕

According to the present invention, in a tire having a tread pattern with different pitch lengths in the tire circumferential direction, the grooves in the normal direction of the tire tread surface of the minor grooves constituting the unit pitch are determined according to the size of the groove area ratio per unit pitch. By increasing the wall angle, the thickness unevenness of the tread rubber layer in the tire circumferential direction is reduced and uniformity is improved.This reduces the noise of tires with block patterns, and also improves its superiority. It is possible to reduce vibrations during driving and improve ride comfort while maintaining the appearance of the tread surface.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views along the tire circumferential direction showing one example of blocks constituting the trend surface of the tire of the present invention, and Figure 2 shows an example of the tread portion of a conventional tire. FIG. 3 is a perspective view showing the groove volume ratio per pitch, and FIG. 4 is a plan view of the tread pattern of the test tire (Example, Comparative Example). 1... Main groove, 2... Minor groove, 3... Belt layer, 4...
...Block, Pn...Pitch length. Agent Patent Attorney Nobuo Ogawa −

Claims (2)

[Claims] (1) In a tire having a tread pattern consisting of blocks having different pitches in the tire circumferential direction, 1
A pneumatic tire characterized in that the groove wall angle of the sub-groove constituting a unit pitch in the normal direction of the tire tread surface is increased in accordance with the size of the groove area ratio per pitch. (2) The difference Δθ between the groove wall angles θmax and θmin in the normal direction of the tire tread surface of the sub-grooves forming the unit pitch with the maximum groove area ratio and the unit pitch with the minimum groove area ratio is at least 5. 2. The pneumatic tire according to claim 1, wherein the pneumatic tire has an angle of .degree.