Pipes and tubular conduits – Flexible – Corrugated
Reexamination Certificate
2000-02-28
2001-04-17
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Flexible
Corrugated
C138S109000, C138S118000
Reexamination Certificate
active
06216743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bellows tube, more specifically the bellows tube for use in an exhaust system of an automotive vehicle.
2. Description of the Related Arts
In general, a flexible tubular joint is employed in a vehicle exhaust system at a connecting portion of exhaust pipe, so as to absorb a vibration of an engine or a relative displacement between the engine and the exhaust pipe. Once a bending moment or shearing stress is applied to the flexible tubular joint, which may be called as a flexible tube, the moment and stress applied thereto will be the maximum at an end portion of the flexible tube, i.e., the connecting portion. In order to improve durability of the tube, various countermeasures have been proposed, heretofore. In Japanese Patent Laid-open Publication No.8-28260, for example, disclosed is a flexible tube which is formed of a metal tube
21
having a bellows portion
23
with a mountain portion
25
and a valley portion
27
formed alternately, wherein a circular arc portion
29
is formed on the top of the mountain portion
25
and the bottom of the valley portion
27
, respectively. According to the Publication, it is proposed that the heights of the fourth mountain M
4
and following mountains are made equal, and the heights of the third mountain M
3
, second mountain M
2
and first mountain M
1
are gradually lowered toward the end of the bellows portion
23
, and that the radius of curvature of the circular arc portion
29
formed at a rising portion
31
of the first mountain M
1
is made more than two times as large as the radius of curvature of the circular arc portion
29
formed at each top of the fourth mountain M
4
and following mountains.
In Japanese Utility Model Laid-open Publication No.1-166886, with respect to a tube connecting apparatus for connecting one tube with the other one tube through a bellows tube, and protecting the outer side of the bellows tube by an outer protecting cylinder, it is proposed that a large diameter portion of the outermost end the bellows tube is made longer than other large diameter portions.
In Japanese Patent Laid-open Publication No.61-235025, there is disclosed a method for manufacturing an &OHgr;-type bellows, which includes a first process for forming a tube blank to provide a U-shaped mountain portion and a straight tube portion crossed normal to the bottom of the mountain portion, with a predetermined space formed between them, a second process for compressing the tube blank in its axial direction by a predetermined length, with an inside pressure applied to the tube blank formed by the first process, and a third process for applying high pressure into the tube blank for a predetermined period, with the tube blank compressed.
According to the flexible tubular joints disposed in the exhaust pipe of the vehicle including the flexible tube as disclosed in the publications listed above, outwardly curved portions of a metal tube (designated as the mountain portion in the Publication No.8-28260) which are curved outward of the metal tube, and inwardly curved portions (designated as the valley portion in that Publication) which are curved inward of the metal tube, are formed to provide a generally &OHgr;-shaped cross section, respectively, to improve a resiliency.
In the Publication No.8-28260, it is aimed to lessen a concentration of stress to the end portion, by enlarging the radius of curvature of the circular arc portion formed at the rising portion of the first mountain. As a result, a damage can be avoided at the rising portion, but a possible damage may be made at a portion near the top of the first mountain. This is because, the mountain portion of the first mountain is formed on the metal tube by a general bulging process, so that the thickness of the bulged first mountain is reduced comparing with that of the metal tube before it is bulged, and also because an inflection point is made on a connecting portion between the first mountain and the end of the rising portion following the first mountain, to weaken a portion at the point. Furthermore, if a bending deformation is made on the flexible tube, the stress will be concentrated on the portion near the top of the first mountain. Therefore, the tube is likely to be broken at the inflection point.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a bellows tube formed of metal having a cylindrical collar portion and a plurality of corrugations adjacent thereto with outwardly curved portions and inwardly curved portions alternately formed along the longitudinal axis of the tube, wherein an end portion of the corrugations is formed in a shape capable of withstanding repeated loads appropriately, to provide a sufficient durability.
It is another object of the present invention to provide a method for forming the bellows tube.
In accomplishing the above and other objects, a bellows tube formed of metal includes a cylindrical collar portion and a plurality of corrugations adjacent thereto with outwardly curved portions and inwardly curved portions alternately formed along the longitudinal axis of the tube. The bellows tube further includes a bulged end portion extending from a first outwardly curved portion of the outwardly curved portions toward the collar portion. The bulged end portion is bulged outward of the tube, with the outer diameter of the bulged end portion gradually reduced from the first outwardly curved portion to the collar portion. And, a connecting end portion is formed to connect the bulged end portion with the collar portion, and formed to be curved inward of the tube.
Preferably, the radius of curvature of the connecting end portion is smaller than the radius of curvature of the first outwardly curved end portion.
The outwardly curved portions, inwardly curved portions, and connecting end portion are preferably formed to provide a substantially circular cross section, respectively.
The outwardly curved portions and inwardly curved portions are preferably formed to provide a generally &OHgr;-shaped cross section, respectively.
And, a method is provided for forming a straight metal tube to produce a bellows tube having a cylindrical collar portion and a plurality of corrugations adjacent thereto, with outwardly curved portions and inwardly curved portions alternately formed along the longitudinal axis of the metal tube. The method is achieved by forming a bulged end portion extending from a first outwardly curved portion of the outwardly curved portions toward the collar portion, and bulged outward of the metal tube, with the outer diameter of the bulged end portion gradually reduced from the first outwardly curved portion to the collar portion, and forming a connecting end portion for connecting the bulged end portion with the collar portion, to be curved inward of the metal tube.
REFERENCES:
patent: 4340089 (1982-07-01), Freiherr von Arnim et al.
patent: 5704401 (1998-01-01), Fukui et al.
patent: 0 493 680 A1 (1992-07-01), None
patent: 0 736 714 A1 (1996-10-01), None
patent: 61-235025 (1986-10-01), None
patent: 1-166886 (1989-11-01), None
patent: 8-28260 (1996-01-01), None
Kihira Hiroyuki
Kosaki Shinji
Suzuki Susumu
Brinson Patrick
Oliff & Berridg,e PLC
Sango Co. Ltd.
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