Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1998-04-09
2004-02-10
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S902000
Reexamination Certificate
active
06688356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire in which pattern noise is reduced while other properties (in particular, performance on wet road surfaces) are maintained.
2. Description of the Related Art
Lug grooves, which endow a pneumatic tire with performance on wet road surfaces and resistance to hydroplaning in particular, are indispensable to pneumatic tires.
However, due to the existence of lug grooves, pitch noise (impact noise) is generated at the time the leading (step-in) edge of a block of the pneumatic tire contacts a road surface.
Various studies have been conducted in order to determine methods of reducing the pattern noise generated from the lug grooves (pitch noise being the main type of pattern noise). In particular, pitch variation, transverse direction phase offsetting, and the like have been studied in an attempt to reduce pattern noise.
Generally, there is a correlation between the negative ratio, the sound level, and the performance on wet road surfaces. If the negative ratio is reduced, the sound level improves, but the performance on wet road surfaces deteriorates. If the negative ratio is increased, the performance on wet road surfaces improves, but the sound level deteriorates.
SUMMARY OF THE INVENTION
In view of the aforementioned, an object of the present invention is to provide a pneumatic tire in which pattern noise can be reduced without a deterioration in the performance on wet road surfaces.
As illustrated in
FIG. 10
, impact noise is generated when a tire
100
rotates and a block
102
contacts a road surface
104
. (Hereinafter, this impact noise will be called “pitch noise”, and the waveform thereof is illustrated in
FIG. 11.
)
When the pattern of a tread is being designed, the angle of the edge portion of the block is an important factor. Therefore, the present inventors studied the angle of the block edge portion.
Due to the existence of lug grooves, pitch noise is generated when the leading edge of a block contacts the road surface.
It is known that the magnitude of the pitch noise is determined by the angle formed by the tire leading edge side contour line of the ground-contact configuration and the side surface of the block leading edge side.
More specifically, as illustrated in
FIG. 12
, when an angle &thgr; (hereinafter, “ground-contact angle &thgr;”), which is formed by a tire leading edge side contour line
106
of the ground contact configuration and the tire circumferential direction (the direction of arrow A and the direction of arrow B), is equal to an angle &phgr; of the leading edge of the block
102
(the angle formed by a side surface
102
A of the leading edge side of the block
102
and the tire circumferential direction), i.e., when the tire leading edge side contour line
106
of the ground-contact configuration and the side surface
102
A of the leading edge side of the block
102
are parallel (i.e., when &phgr;=&thgr;), as illustrated in
FIG. 13
, the pitch noise is greatest. When the tire leading edge side contour line
106
of the ground-contact configuration and the side surface
102
A of the leading edge side of the block
102
are orthogonal (i.e., when the difference between &thgr; and &phgr; is 90°), the pitch noise is lowest. (Note that in a case in which the tire leading edge side contour line is curved, as shown in
FIG. 12
, the ground-contact angle &thgr; is the angle formed by the tire circumferential direction and a tangent line SL which passes through a point tangent to the block
102
leading edge (the end portion which first contacts the ground).)
The angular difference between &thgr; and &phgr; is important to the reduction of pitch noise.
Here, the relationship between the tire leading edge side contour line
106
of the ground-contact configuration and the side surface
102
A of the leading edge side of the block is considered.
First, in a case in which blocks are provided at the left and right of the tire equatorial plane, the angles at the respective portions are set as illustrated in
FIGS. 14A and 14B
. Namely, with respect to a block
102
R at the right side of a tire equatorial plane CL, the angles are defined in the clockwise direction. The angle at the block leading edge is &phgr;
1
, and the ground-contact angle formed by the tire circumferential direction and the tire leading edge side contour line
106
of the ground-contact configuration is &thgr;
1
.
On the other hand, with respect to a block
102
L at the left side of the tire equatorial plane CL, the angles are defined in the counterclockwise direction. The angle at the block leading edge is &phgr;
2
, and the ground-contact angle formed by the tire circumferential direction and the tire leading edge side contour line
106
of the ground-contact configuration is &thgr;
2
.
The positional relationships among the tire leading edge side contour line
106
, the side surface
102
A of the leading edge side of the block
102
R at the right side of the tire equatorial plane CL, and the side surface
102
A of the leading edge side of the block
102
L at the left side of the tire equatorial plane CL, are as follows.
Assuming that &bgr;>0°, &agr;
1
>0°, and &agr;
2
>0°, then &thgr;
1
=90°+&bgr;, &thgr;
2
=90°+&bgr;, &phgr;
1
=90°−&agr;
1
, and &phgr;
2
=90°+&agr;
2
.
As described above, the angular difference between the ground-contact angle &thgr; and the angle &phgr; of the block leading edge is important to pitch noise. The angular difference &THgr;
1
of the block
102
at the right side of the tire equatorial plane CL is &THgr;
1
=&thgr;
1
−&phgr;
1
=&bgr;+&agr;
1
, and the angular difference &THgr;
2
of the block
102
at the left side of the tire equatorial plane CL is &THgr;
2
=&phgr;
2
−&thgr;
2
=&agr;
2
−&bgr;. The relationship between the angles and the magnitude of the pitch noise is as shown in FIG.
15
.
FIG. 15
illustrates that pitch noise of a magnitude P
1
is generated from the block
102
at the right side of the tire equatorial plane CL, and pitch noise of a magnitude P
2
is generated from the block
102
at the left side of the tire equatorial plane CL. (&THgr;
2
<&THgr;
1
, and therefore, the magnitudes of the pitch noise are P
2
>P
1
.)
One conventional method of reducing pitch noise centers around the tire transverse direction phase offsetting of blocks. In the present invention as well, the phases of the left and right blocks are offset by a dimension D in the tire circumferential direction.
By providing a phase difference for respective pitch noises generated from block rows of blocks (generally, pairs of left and right blocks with respect to an axis extending along the tire circumferential direction (e.g., the tire equatorial plane CL)), the sounds can cancel each other out. The necessary extent of the phase difference differs in accordance with the configurations or the like of respective tires, and is determined for each tire.
As illustrated in
FIGS. 16A and 16B
, two sounds (Â and {circle around (B)}) are completely reverse phases. When the magnitude of the amplitude Pa and the magnitude of the amplitude Pb are equal, the magnitude of the combined sound is a minimum (FIG.
16
B). However, when there is a difference between the amplitudes, the magnitude of the combined sound is not zero, and a sound having a magnitude of an amplitude |Pa−Pb| remains (see FIG.
16
A).
It can thus be understood that, in order to make the phase offsetting effect a maximum, the magnitudes of the amplitudes of the sounds generated by the respective subject blocks must be equal.
Here, in
FIGS. 14A and 14B
, the angles of inclination of the lug grooves are equal, i.e., the side surface
102
A of the leading edge side of the block
102
L at the left side of the tire equatorial plane CL and the side surface
102
A of the leading edge side of the block
102
R at the right side of the tire eq
Bridgestone Corporation
Maki Steven D.
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