Metal deforming – Process – Tube making or reshaping
Reexamination Certificate
1999-05-19
2001-09-04
Crane, Daniel C. (Department: 3725)
Metal deforming
Process
Tube making or reshaping
C072S302000
Reexamination Certificate
active
06282939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general methods and devices for producing or reforming a bellows, and more particularly methods and devices for producing or reforming a metal bellows installed in a flexible tube that is disposed in an exhaust pipe line of an automotive internal combustion engine to absorb undesired vibration of the exhaust pipe line and compensate relative displacement between two portions of the exhaust pipe line.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional flexible tube to which a bellows is practically applied will be briefly described with reference to
FIGS. 5 and 6
of the accompanying drawings. The conventional flexible tube depicted by
FIGS. 5 and 6
is described in detail in Japanese Utility Model First Provisional Publication 61-187916.
In
FIG. 6
, there is shown the flexible tube which is generally designated by numeral
100
. As is seen from this drawing, the flexible tube
100
is a device arranged to connect upstream and downstream exhaust pipes “UP” and “DP” of an exhaust pipe line in such a manner as to absorb the vibration of the pipe line, and/or compensate a relative displacement between the two pipes “UP” and “DP”.
The flexible tube
100
comprises a metal bellows
102
that has an upstream end tightly disposed on a downstream end of the upstream exhaust pipe “UP” and a downstream end tightly disposed on an upstream end of the downstream exhaust pipe “DP”. A cover
104
of braided metal wire covers or encloses the bellows
102
having an upstream end tightly disposed on the upstream end of the bellows
102
and a downstream end tightly disposed on the downstream end of the bellows
102
. For the tight mounting of the upstream and downstream ends of both the bellows
102
and the cover
104
onto the upstream and downstream exhaust pipes “UP” and “DP”, respective metal collars
106
and
108
are tightly disposed on the upstream and downstream ends of the cover
104
, as shown. The bellows
102
can absorb vibration transmitted thereto from an internal combustion engine (not shown) through the upstream exhaust pipe “UP”. That is, upon receiving vibration, the bellows
102
is subjected to a certain resilient deformation due to the nature thereof, which absorbs the vibration and compensates a relative displacement between the upstream and downstream pipes “UP” and “DP”.
The cover
104
functions to restrict an excessive elongation of the bellows
102
and to protect the bellows
102
from being hit by small stones or the like flying from the road. That is, by a certain length, the cover
104
, which is constructed of braided metal wire, can axially expand following the elongation of the bellows
102
. Thus, when the elongation of the bellows
102
reaches to the certain length, the cover
104
now functions to stop the further elongation of the bellows
102
. That is, due to provision of the cover
104
, the bellows
102
can be protected from making an excessive elongation. In other words, the bellows
102
can expand axially by a certain length within the cover
104
.
For assembling the flexible tube
100
, the metal bellows
102
is reformed before being put into the cover
104
. That is, the metal bellows
102
is subjected to a so-called “single compression process” for achieving both a dimensional stability of the treated bellows
102
and an appropriate axial flexibility of the treated bellows
102
. That is, as is seen from
FIG. 5
, in this compression process, a blank
102
X of the bellows
102
is compressed once to the length “L−a” which is shorter than the normal length “Ls” of the bellows
102
. This compression process is positively carried out for the reason originating from an inevitably occurring “spring-back phenomenon” of the compressed bellows
102
Y. In fact, due to this spring-back phenomenon, after the compression, the over-compressed bellows
102
Y gradually expands to have the normal length of “Ls”. Furthermore, due to this compression, the pitch of bulges of the treated bellows
102
becomes small causing each bulge to have a generally &OHgr;-shaped cross section, which brings about an appropriate axial flexibility or resilient deformation of the bellows
102
.
However, it has been revealed that the above-mentioned single compression of the bellows
102
X leaves in the bellows
102
a stress (or residual stress) of a type that causes the bellows
102
to expand in an axial direction when heated.
Accordingly, when the flexible tube
100
having the above-mentioned bellows
102
installed therein is practically used, that is, used in an exhaust pipe line of the engine, the entire length “Ls” of the bellows
102
tends to increase due to releasement of the residual stress by the heat of the exhaust gas from the engine. The increase in the entire length “Ls” of the bellows
102
however means a reduction in the certain length by which the bellows
102
can expand axially within the cover
104
. That is, a so-called “elongation flexibility” of the bellows
102
is reduced or lowered at the time when the flexible tube
100
is being practically used.
The expansion/contraction of the bellows
102
is carried out while being interrupted by the cover
104
. The cover
104
has such a structure as to reduce its diameter when axially expanded. Thus, elongation of the bellows
102
caused by application of the exhaust gas heat thereto brings about elongation of the cover
104
and thus reduces the diameter of the same. Reduction in diameter of the cover
104
narrows an annual space defined between the bellows
102
and the cover
104
, which causes an obstacle to the elongation flexibility of the bellows
102
. This fact will be understood from the graph of FIG.
4
.
The graph of
FIG. 4
shows a relationship between the force “F” needed for elongation of a bellows and the elongation “E” of the bellows. In the graph, the solid line curve represents the elongation flexibility possessed by a normally dimensioned bellows
102
A installed in the cover
104
, which has the normal length “Ls” and the critical elongation “S”. As is seen from this graphs in the normally dimensioned bellows
102
A, within the region of the critical elongation “S”, the elongation “E” of the bellows
102
A increases substantially in proportional to the elongation force “F” applied to the bellows
102
A. While, when the elongation “E” extends beyond the critical elongation “S”, the elongation force “F” suddenly increases and thus the elongation flexibility of the bellows
102
A is lowered. The broken line curve represents the elongation flexibility possessed by a bellows
102
B somewhat expanded due to the exhaust gas heat applied thereto, which has the length “Ls
1
” greater than “Ls” and the critical elongation “S
1
” smaller than “S”. As is seen from the graph, in this bellows
102
B, due to the reduction in critical elongation, the sudden increase of the elongation force “F” appears at an initial stage of the elongation “E”. This means that the elongation flexibility of the bellows
102
B is poor as compared with that of the bellows
102
A. The phantom line curve represents the elongation flexibility possessed by a bellows
102
C somewhat shorter than the bellows
102
A due to excessive compression applied thereto, which has the length “LS
2
” smaller than “Ls” and the critical elongation “S
2
” greater than “S”. Although this bellows
102
C can provide a sufficient elongation under the practical use, the shorter initial length “Ls
2
” of the bellows
102
C brings about a difficulty with which the bellows
102
C is installed in the cover
104
. That is, in this case, the flexible tube
100
assembled fails to have a normally dimensioned structure. According to tests executed by the inventors, the following acts have been further revealed. That is, when a bellows of the length of about 300 mm that has been subjected to a single compression process is left in a room temperature, the bellows is expanded or elongated by about 2 mm. W
Kajiura Yoshiyuki
Minamidate Tadahiro
Calsonic Kansei Corporation
Crane Daniel C.
Foley & Lardner
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