JPH0585107A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To satisfactorily realize the driving stability on a dry road and the drainage performance on a wet road irrespective of the straight traveling or the cornering traveling by specifying the angle of the main grooves relative to the circumferential direction of a tire. CONSTITUTION:The front end line of the ground contact shape of a tread surface 1 is formed as an approximate arc 5 with its radius (R) of a circle connecting a point (a) where the center line (S) passing the center of the tread ground contact width (W) and extending in the circumferential direction of a tire crosses the front end line of the ground contact shape, and points (b), (c) where lines which extend parallel to the centerline at the distance of 40% of the tread ground contact width (W) from the center line on each side in the tire width direction cross the front end line of the ground contact shape. This radius (R) is made less than 2 times the tread ground contact width (W), and a plurality of main grooves 2 extending in the radial direction from the tread center area 7 toward the right and the left shoulder parts 8 are provided on the tread surface. The angle theta of the main grooves relative to the circumferential direction of the tire is set to stay in the range determined by the formula (I) when the angle theta and the distance (W) are measured at the position separate from the center line by the distance (W) in the tire width direction while defining the outer direction of a vehicle being positive when the tire is fitted to the vehicle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire which has both steering stability on dry roads and drainage on wet roads.

[0002]

2. Description of the Related Art The steering stability on a dry road of a pneumatic tire is improved as the groove area ratio of the tread surface is smaller.
On the contrary, the drainage property on the wet road can be improved by increasing the groove area ratio of the tread surface. As described above, the steering stability on a dry road and the drainage property on a wet road are in a mutually contradictory relationship.

[0003] Conventionally, as a measure for achieving both the steering stability on a dry road and the drainage on a wet road, which are in such a relationship of standing upright, for example, a straight groove is provided in the tire circumferential direction, or a straight groove is used. A combination of V-shaped sub-grooves arranged over the entire ground contact width has been proposed. However, it was difficult to make them compatible at the same time.

On the other hand, the present inventor has previously formed the grounding front end line of the grounding shape of the tread surface as an approximate arc according to Japanese Patent Application Laid-Open No. 3-82610 and for the same purpose, the direction of the main groove is the approximate arc. It was proposed that the angle was within ± 10 ° with respect to the normal line. This tire substantially satisfied the above-mentioned object in terms of performance when traveling straight ahead, but had a drawback that the above-mentioned object was not sufficiently achieved during cornering.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a pneumatic tire capable of satisfactorily achieving both steering stability on a dry road and drainage on a wet road regardless of whether the vehicle is running straight or cornering. To provide.

[0006]

A pneumatic tire of the present invention that can achieve the above object has a ground contact front end line of a ground contact shape on a tread surface, and a center of a tread ground contact width W is arranged in the tire circumferential direction. An intersection a where the extending center lines intersect, and a tread contact width W of 40 from the center line to the left and right in the tire width direction.
Is formed as an approximate arc of a radius R passing through intersections b and c at which parallel lines extending parallel to the center line at a distance of%, and the size of the radius R is smaller than R ≦ with respect to the tread ground contact width W. A plurality of main grooves radially extending from the center region of the tread to the left and right shoulders are provided on the tread surface, and the angle θ of the main grooves with respect to the tire circumferential direction is set to 2W.
When the angle θ and the distance w are measured as + in the vehicle outer direction when the vehicle is mounted at a position separated from the center line by a distance w in the tire width direction, the following formula 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -38 ≤ θ ≤ 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -14.

However, the unit of θ is deg. Here, the ground contact front end line of the tire is a non-contact point with the front end part of the ground contact surface in the traveling direction of the vehicle on the ground contact surface of the tread surface when a normal load according to JATMA or ETRTO is applied to the pneumatic tire. The boundary line with the ground. Further, the approximate arc to which the grounding front end line of the tread surface is approximate, an intersection point where a centerline extending the grounding width center of the tire tread surface in the tire circumferential direction intersects the grounding front end line, and the tire width direction from the centerline. A circular arc that includes two intersections where line segments extending in the tire circumferential direction at a position 40% of the tread ground contact width to the left and right intersect with the ground contact front end line.

By the way, when a tire mounted on a vehicle travels on a wet road, observing the draining direction of the water discharged at the front ground contact line on the tread surface, it is found that the direction is almost normal to the front ground contact line. I understand. Based on such knowledge, the present invention has a shape in which the grounding front end line of the tread surface can be efficiently drained, and sets the direction of the groove that greatly contributes to the drainage action.

In the present invention, the grounding front end line of the tread surface must be set so that the radius R of the approximate circular arc defined above has a relationship of R≤2W with respect to the grounding width W.
That is, the grounding front end line of the tire of the present invention has better drainage effect at the grounding front end when it is as close to a circle as possible,
If it is made large enough to exceed 2 W, the ground contact surface will have a shape close to a square. As described above, the ground contact surface shape close to a square is inferior in drainage effect at the front edge compared to the ground contact surface shape close to a circle.

In the present invention, the angle θ of the main groove radially extending from the central region of the tread to the left and right shoulders with respect to the tire circumferential direction is a position separated from the center line extending in the tire circumferential direction by a distance w in the tire width direction. In the above, the angle θ and the distance w are set to +
When measured as: 285 (w / W) ³ +52 (w / W) ² +70 (w / W) −38 ≦ θ ≦ 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -14. Where θ
The unit of is deg. As a result, the flow resistance at the time of draining from the main groove at the ground contact front end of the tread surface can be reduced regardless of whether the vehicle is traveling straight ahead or cornering, and efficient drainage can be performed.

The pneumatic tire of the present invention will be described below with reference to the drawings. FIG. 1 is a development view of a tread pattern of a pneumatic tire according to the present invention. A tread surface 1 is provided with a plurality of main grooves 2 extending from a tread central area 7 to a shoulder portion 8. The angle θ of the main groove 2 with respect to the tire circumferential direction is the angle θ and the distance w at a position separated from the center line S extending in the tire circumferential direction by a distance w in the tire width direction, and + in the vehicle outer direction when the vehicle is mounted. Then, the following formula 285 (w / W) ³ +52 (w / W) ² +70 (w / W) −38 ≦ θ ≦ 285 (w / W) ³ +52 (w / W) ² +70 (w / W) It is within the range defined by -14.

However, the unit of θ is deg, and W is the tread contact width. The above formula was determined based on the following grounds. That is, in FIG. 5, the mark □ indicates the tire width direction position w / W in the straight running ground contact shape shown in FIG.
And the angle θ is plotted. Similarly, the mark ● is a plot of the relationship between the tire width direction position w / W and the angle θ in the grounding shape during cornering travel shown in FIG. 4. Here, in order to achieve both drainage performance during straight traveling and during cornering traveling, the w / W
For each of the above, the above-mentioned angle θ during straight traveling and cornering traveling is averaged and plotted, and is marked with a circle. Therefore, the object of the present invention can be achieved by determining the w / W and the angle θ as indicated by the circles in FIG.

However, since it is difficult to design the actual pattern only with the plotted points in FIG. 5, it is necessary to continuously indicate the groove angle θ at any position w / W in the tire width direction. When the plotted points are approximated by a cubic expression, a curve like a solid line is obtained, which is represented by θ = 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -26. However, the unit of θ is deg.

Here, the maximum amount of deviation between the above-mentioned approximate expression and the circled plot points is ± 12 °. However, even if the groove angle is determined by the above-mentioned approximate expression, the present invention can be achieved, as will be shown in the examples described later. The effect is obtained. Also, theoretically, from the above approximation,
The effect can be obtained even at an angle such as a circle marked with a 12 ° shift. 285 (w / W) ³ +52 (w / W) ² +70 (w / W) −38 ≦ θ ≦ 285 (w / W) ³ Θ was determined in the range of +52 (w / W) ² +70 (w / W) −14.

With such a groove arrangement, when the tire steps on the filmy water surface, the flow resistance at the time of draining from the main groove 2 at the front end of the tire ground contact surface 3 is reduced both during straight running and during cornering. It has become. The approximate arc 5 is, as shown in FIG. 2, an intersection a where a center line S extending in the tire circumferential direction at the center of the contact width of the tire contact surface 3 intersects with the ground contact front end line 4, and the center line S is grounded to the left and right respectively. Line segments B and C extending in the tire circumferential direction at positions separated by 40% of the width W are defined by arcs including two intersections b and c that intersect the ground contact front end line 4, respectively. The radius R of the approximate arc 5 has a relationship of R ≦ 2W with respect to the ground contact width W.

When a pneumatic tire having the above-mentioned tread pattern is mounted on a passenger car and then travels on a wet road, when the film-like water covering the road surface travels straight, as shown in FIG. Is almost uniformly and efficiently repelled near the normal direction over the entire area of.
Also, during cornering, as shown in FIG. 4, the tire is repelled almost uniformly and efficiently over the entire front ground contact end line 4a of the tire in the vicinity of its normal direction. Note that FIG.
The sub-groove 6 may be provided as shown in FIG.

[0017]

EXAMPLE A tire of the present invention having a tread pattern as described below, a conventional tire, and comparative tires 1 and 2 were trial-produced on a tread surface of a tire having a tire size of 255 / 40ZR17. When the tire goes straight, the groove area ratio of the ground contact surface is set to 28.2% as a whole, and when the tread surface is divided into five equal parts in the tire width direction, the groove area ratio in each area is mounted on the vehicle. Sometimes from the inside, 2
7.5%, 29.5%, 28.6%, 29.1% and 2
It was set to be 6.4%.

Tire of the present invention : As shown in FIG. 7, a plurality of main grooves 2 are installed so that the angle θ formed by the center line 2'and the center line S of the tire satisfies the following equation. θ = 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -26 However, the unit of θ is deg.

Conventional tire : As shown in FIG. 8, five main grooves 2a extending in the circumferential direction are provided. Comparative tire 1 : As shown in FIG. 9, five main grooves 2a extending in the circumferential direction and a V shape (the apex is on the main groove in the center of the tire)
And the sub-groove 6a. Comparison tire 2 :

As shown in FIG. 10, it is constituted by five main grooves 2a extending in the circumferential direction and a V-shaped (the apex is the second main groove from the outer side of the vehicle body) auxiliary groove 6b. Each of these four types of tires was assembled into a rim of 17 × 9J, and the air pressure was adjusted to 2.3 kgf / cm ^2, and then the 2600cc domestic car was produced.
Then, as shown in FIG. 9, the device was mounted, and the hydroplaning generation speed on the wet road and the wet circular turning limit speed were evaluated. The results are shown in "Table 1". Further, the cornering force measured by an indoor cornering tester as a substitute for the steering stability on a dry road is shown in "Table 1".

[0021] In Table 1, the index is shown with the measured value of the conventional tire being 100. Therefore, the larger the index, the better. Further, the hydroplaning generation rate and the like were measured as follows. That is, cornering force : The cornering force was measured with an indoor cornering tester at a load of 450 kgf and a slip angle of 10 ° and expressed as an index.

Hydroplaning generation speed : The speed at which hydroplaning occurred was measured by running straight on a road surface having a water depth of 7 mm and gradually increasing the speed. Wet circle turning speed : Radius 3 on a road surface with a water depth of 5 mm
The maximum speed at which a side slip was first generated was measured when a circle was turned at 0 m. It can be seen from Table 1 that the tire of the present invention has better steering stability on dry roads and better drainage on wet roads during straight running and cornering running than the conventional tires and comparative tires 1 and 2. I understand.

[0023]

As described above, according to the present invention, the ground contact front end line of the ground contact shape of the tread surface is defined as an intersection a where the center line extending in the tire circumferential direction at the center of the tread ground contact width W intersects with the ground contact front end line. , A radius R passing through intersections b and c at which parallel lines extending parallel to the center line intersect at a distance of 40% of the tread ground contact width W to the left and right in the tire width direction from the center line.
And the radius R is set to R ≦ 2W with respect to the tread ground contact width W, and a plurality of main grooves extending radially from the tread central region to the left and right shoulders are formed on the tread surface. When the angle θ of the main groove with respect to the tire circumferential direction is measured at a position separated by a distance w from the center line in the tire width direction, the angle θ and the distance w are measured with the vehicle outer direction when the vehicle is mounted as +, By the following formula 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -38 ≤ θ ≤ 285 (w / W) ³ +52 (w / W) ² +70 (w / W) -14 Since the range is set, it is possible to satisfactorily achieve both steering stability on dry roads and drainage on wet roads regardless of straight running or cornering.

[Brief description of drawings]

FIG. 1 is a development view of a tread pattern of a pneumatic tire according to the present invention.

FIG. 2 is an explanatory diagram of an approximate circular arc that approximates a front ground contact line of a tire.

FIG. 3 is an explanatory diagram showing a ground contact surface shape and a drainage direction during straight traveling.

FIG. 4 is an explanatory diagram showing a ground contact surface shape and a drainage direction during cornering.

FIG. 5 is a diagram showing a relationship between a tire width direction position and a groove angle.

FIG. 6 is a perspective view showing another example of a pneumatic tire according to the present invention.

FIG. 7 is an explanatory view showing a state in which the tire of the present invention is mounted on a vehicle.

FIG. 8 is an explanatory view showing a state in which a conventional tire is mounted on a vehicle.

FIG. 9 is an explanatory diagram showing a state in which the comparative tire 1 is mounted on a vehicle.

FIG. 10 is an explanatory view showing a state in which the comparative tire 2 is mounted on the vehicle.

[Explanation of symbols]

 1 tread surface 2 main groove 4 front contact line 5 approximate arc 7 central tread area 8 shoulder part a, b, c intersection B, C line segment R radius R S center line W tread contact width w distance θ angle

Claims (1)

[Claims] 1. A ground contact front end line of a ground contact shape on a tread surface, and an intersection point a at which a center line extending in the tire circumferential direction around the center of the tread ground contact width W intersects with the ground contact front end line and a tire width direction from the center line. It is formed as an approximate arc of a radius R passing through intersections b and c where parallel lines extending in parallel with the center line at a distance of 40% to the left and right of the tread ground contact width W, and the size of the radius R is set. R ≦ 2 W with respect to the tread ground contact width W, and a plurality of main grooves extending radially from the tread central region to the left and right shoulders are provided on the tread surface, and the angle θ of the main grooves with respect to the tire circumferential direction is When the angle θ and the distance w are measured at a position separated from the center line in the tire width direction by a distance w with the vehicle outer direction when the vehicle is mounted being +, the following formula 285 (w / W) ³ +52 (w / W) ² +70 w / W) -38 ≦ θ ≦ 285 (w / W) 3 +52 (w / W) 2 +70 (w / W) pneumatic tire in a range defined by -14.