Heavy duty radial tire having tapered shoulder portions

Details Heavy duty radial tire having tapered shoulder portions Heavy duty radial tire having tapered shoulder portions

1999-02-03

2001-02-27

Maki, Steven D. (Department: 1733)

Resilient tires and wheels

Tires, resilient

Anti-skid devices

C152S209180, C152S209220

Reexamination Certificate

active

06192953

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a pneumatic tire, more particularly to a heavy duty radial tire having an improved tread portion being capable of reducing uneven wear in tread shoulder regions without sacrificing the wandering performance and traction performance.
DISCUSSION OF RELATED ART
In general, heavy duty tires for construction vehicles such as dump trucks are provided with a rib-type tread pattern, wherein in order to obtain a good traction performance under off-road conditions, circumferentially extending main grooves are provided with a zigzag configuration and lateral grooves called lug groove are disposed in the axially outmost ribs or shoulder ribs. Further, in order to improve the wandering performance, the shoulder portions are tapered.
In such tires, due to zigzag main grooves and lug grooves, the fluctuation of the ground pressure distribution in the circumferential direction is relatively large in the shoulder ribs in particular. Therefore, uneven wear is liable to occur on both sides of the lug grooves in the circumferential direction and between the main groove and lug grooves, and as a result, the wear life is shortened.
This type of uneven wear may be reduced to some degree by changing the zigzag main groove into a straight configuration, and/or decreasing the length of lug grooves. In this case, however, road grip or traction greatly decreases.
On the other hand, as the shoulder portions are tapered, the length of the lug grooves is decreased, which also deteriorates the traction performance.
It is therefore, an object of the present invention to provide a heavy duty radial tire, especially for construction vehicle such as dump trucks, in which uneven wear of shoulder ribs is effectively improved without sacrificing the traction and wandering performances.
SUMMARY OF THE INVENTION
According to the present invention, a heavy duty radial tire comprises
a tread portion with a pair of tread edges TE,
a pair of tapered shoulder portions each extending axially outwardly and radially inwardly from one of the tread edges TE and having an slope angle &agr; of from 40 to 50 degrees with respect to the normal direction to the tread surface
2
S at the tread edge TE,
a pair of circumferentially extending zigzag main grooves disposed in the tread portion so as to form a pair of shoulder ribs each defined between one of the zigzag main grooves and the adjacent tread edge TE,
the shoulder ribs provided with lug grooves each having an axially inner end P
1
terminated in the rib and an axially outer end opened at the tread edge TE,
the lug grooves each having a bottom Ys extending from the radially outer surface to the axially outer surface of the shoulder rib while inclining at an angle &bgr; with respect to the normal direction to the tread surface
2
S at said axially inner end P
1
,
the height H
1
of the tapered shoulder portion measured from the taper end
9
e
thereof to the tread edge TE along the normal direction to the tread surface
2
S at the tread edge TE being in the range of from 50 to 67% of the depth Hg of the zigzag main grooves,
the angle &agr; at the tread edge TE being larger than the angle &bgr; at said axially inner end P
1
,
the distance LA between said axially inner end P
1
and the zigzag main groove being in the range of from 0.95 to 1.15 times the minimum distance LB between the zigzag main groove and the tread edge TE, each distance measured in the axial direction along the tread surface
2
S,
the distance LD from said taper end
9
e
to the bottom Ys of the lug groove measured in parallel with the tread surface
2
S along the axial direction being larger than the distance LC from the tread edge TE to said axially inner end P
1
measured in the axial direction along the tread surface.


REFERENCES:
patent: 3858633 (1975-01-01), Boileau
patent: 4362201 (1982-12-01), Zinnen et al.
patent: 5211780 (1993-05-01), Kabe et al.
patent: 3615666 (1986-11-01), None
patent: 14404 (1980-08-01), None
patent: 5-51492 (1993-03-01), None
patent: 5-286310 (1993-11-01), None
patent: 6-166302 (1994-06-01), None

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