Method and device for producing bellows

Information

  • Patent Grant
  • 6386012
  • Patent Number
    6,386,012
  • Date Filed
    Monday, July 9, 2001
    23 years ago
  • Date Issued
    Tuesday, May 14, 2002
    22 years ago
Abstract
In order to produce a metal bellows of a length of “Ls” for use in a heated atmosphere, the following steps take place. First, a blank of the bellows is prepared, which is a metal pipe having a plurality of bulges formed therearound. The blank has a length of “L” that is longer than the length “Ls”. Then, the blank is axially compressed by a length of “a”, so that the compressed blank has a length of “L−a” that is shorter than the length “Ls”. Then, the compressed blank is axially expanded so that the expanded blank has a length of “L−a+b” that is longer than the length “Ls”. Then, the force that has been applied to the blank is removed, and then the treated blank is left in room temperature until the time when the treated blank becomes to have the length of “Ls” due to the spring-back phenomenon.
Description




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 ω-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 “Ls1” greater than “Ls” and the critical elongation “S1” 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 “Ls2” smaller than “Ls” and the critical elongation “S2” greater than “S”. Although this bellows


102


C can provide a sufficient elongation under the practical use, the shorter initial length “LS2” 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 facts 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. While, when the bellows is practically used or heated by the exhaust gas from an engine, the bellows is expanded or elongated by about 6 to 8 mm. This means that even if the bellows is subjected to the single compression process, a certain stress (or residual stress) is left in the bellows, which causes the bellows to expand in an axial direction particularly when heated. The inventors have further revealed that the stress in the bellows can be sufficiently removed when the bellows is annealed at about 600° C. for about 2 minutes. However, in this case, due to adding of the annealing process, the production process becomes complicated and thus the cost of the flexible tube is increased.




SUMMARY OF THE INVENTION




It is therefore an object of the present invention to provide a method of producing a bellows which is free of the above-mentioned drawbacks.




It is another object of the present invention to provide a producing device with which the method of the present invention can be practically carried out.




According to a first aspect of the present invention, there is provided a method for producing a metal bellows of a length of “Ls” for use in a heated atmosphere. The method comprises the steps of (a) preparing a blank of the bellows, the blank being a metal pipe having a plurality of bulges formed therearound, the blank having a length “L” that is longer than the length “Ls”; (b) axially compressing the blank by a length of “a”, so that the compressed blank has a length of “L−a” that is shorter than the length “Ls”; (c) axially expanding the compressed blank so that the expanded blank has a length of “L−a+b” that is longer than the length “Ls”; (d) removing the force that has been applied to the blank for expanding the same; and (e) leaving the treated blank in a room temperature until the time when the treated blank becomes to have the length of “Ls” due to the spring-back phenomenon.




According to a second aspect of the present invention, there is provided a device for reforming a bellows for use in a heated atmosphere. The bellows is a metal pipe having a plurality of bulges formed therearound. The device comprises a base member; a first clamp device fixedly mounted on the base member, the first clamp device having a first hydraulically actuated clamping means which clamps one tubular end of the bellows when actuated; a second clamp device movably mounted on the base member, the second clamp device having a second hydraulically actuated clamping means which clamps the other tubular end of the bellows when actuated; a hydraulic power source which hydraulically actuates the first and second hydraulically actuated clamping means when assuming ON condition; and an electric moving device which moves the second clamp device toward and away from the first clamp device when electrically energized.











BRIEF DESCRIPTION OF THE DRAWINGS




Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which:





FIG. 1

shows bellows producing or reforming steps employed in a method according to the present invention;





FIG. 2

is a partially sectioned front view of a bellows producing or reforming device which practically execute the method of the present invention;





FIG. 3

is an enlarged view of the part indicated by reference “A” in

FIG. 2

;





FIG. 4

is a graph showing the characteristics of three bellows in terms of a relationship between the force needed for elongation of the bellows and the elongation of the bellows;





FIG. 5

shows bellows producing or reforming steps employed in a conventional method; and





FIG. 6

is a partially sectioned front view of a flexible tube to which the bellows produced or reformed by the conventional method is applied.











DETAILED DESCRIPTION OF THE INVENTION




In the following, the method of the present invention, through which a bellows


2


is produced or reformed, will be described in detail with reference to

FIGS. 1

to


3


of the accompanying drawings. The shape of the bellows


2


produced by the method is substantially the same as that of the bellows


102


employed in the conventional flexible tube


100


of FIG.


6


. For ease of description, in the following description, only the term “produce” and its corresponding terms will be used for explaining the method of the invention.




For producing the bellows


2


, the following production steps take plate, which are depicted in FIG.


1


.




That is, first, a blank


2


X of the bellows


2


is prepared. The blank


2


X is a double-layered stainless steel pipe having a plurality of bulges formed therearound. For the production of the blank


2


X, a known hydraulic bulging process is used. That is, to carry out this process, a double-layered stainless straight pipe is set in a split mould whose inner surface is formed with a plurality of annular grooves, and then a certain hydraulic pressure is led into the interior of the pipe to expand the pipe radially outward. With this, the pipe is forced to have therearound a plurality of bulges due to abutment against the grooved inner surface of the mould, that is, the blank


2


X having the length “L” is produced.




Then, the blank


2


X is axially compressed by the length “a” against a counterforce produced by the blank


2


X when compressed, so that the compressed blank


2


Y has the length “La” which is shorter than the normal length “Ls” of the bellows


2


.




Then, the compressed blank


2


Y is axially expanded by the length “b” against a counterforce produced by the blank


2


Y when expanded, so that the expanded blank


2


Z has the length “L−a+b” which is longer than “Ls” but shorter than “L”.




Then, the force for expanding the blank


2


Z is removed. Upon this, the expanded blank


2


Z is forced to contract to have a certain length which is somewhat longer than the normal length “Ls”. Then, the blank


2


Z is left in a room temperature for several minutes. With this, because of the spring-back phenomenon of the blank


2


Z, the blank


2


Z becomes to have the normal length “Ls”. That is, the bellows


2


is produced.




As will be described in detail hereinafter, the bellows


2


thus produced in the above-mentioned manner exhibits excellent performance.




Referring to

FIG. 2

, there is shown a bellows producing device


50


through which the above-mentioned bellows production steps are practically carried out.




The bellows producing device


50


comprises a base member


10


. On the base member


10


, there are mounted first, second, third and fourth stands


12


,


14


,


16


and


18


. The first stand


12


holds thereon both a first hydraulic actuator


20


and a first clamp device


22


. The actuator


20


has a plunger


20




a


that can project toward a center of the first clamp device


22


. The detail of the clamp device


22


will become apparent hereinafter. The second stand


14


holds thereon a guide


24


for the blank


2


X. The second stand


14


rotatably carries a front end portion of a threaded shaft


26


. The third stand


16


rotatably carries a rear end portion of the threaded shaft


26


. The fourth stand


18


holds a servo-motor


28


that has an output shaft connected through a coupling


30


to the rear end of the threaded shaft


26


. Thus, upon energization of the servo-motor


28


, the threaded shaft


26


is rotated about its axis. Disposed on the threaded shaft


26


is a slider


32


that has a threaded bore through which the threaded shaft


26


passes while establishing a meshed engagement therebetween. Although not shown in the drawing, a slider guide is mounted on the base member


10


, which guides an axial movement of the slider


32


while suppressing rotation of the slider


32


about the axis of the threaded shaft


26


. Thus, when, due to energization of the servomotor


28


, the threaded shaft


26


is rotated about its axis, the slider


32


runs in fore-and-aft directions on the threaded shaft


26


. The slider


32


carries thereon a fifth stand


34


. The fifth stand


34


holds thereon both a second hydraulic actuator


36


and a second clamp device


38


which are thus moved together with the slider


32


. The actuator


36


has an output plunger


36




a


that can project toward a center of the second clamp device


38


. As shown, the first and second camp devices


22


and


38


are arranged to face each other. The first and second hydraulic actuators


20


and


36


are connected through a flexible fluid pipe


40


to a pressurized fluid source


42


. Although not shown in the drawing, the fluid source


42


is equipped with an ON/OFF valve by feeding of the fluid pressure from the fluid source


42


to the first and second hydraulic actuators


20


and


36


is controlled.




The detail of the second clamp device


38


will be described with reference to FIG.


3


. Since the first clamp device


22


is substantially the same as the second clamp device


38


, the description of the first clamp device


22


will be omitted.




As is seen from

FIG. 3

, the second clamp device


38


comprises a tubular housing


38




a


in which the output plunger


36




a


of the second hydraulic actuator


36


is axially movably received. As shown, the plunger


36




a


has a tapered leading end. Within the tubular housing


38




a


, there are movably disposed a plurality (viz., three in the illustrated embodiment) of clamp pieces


38




b


that are arranged to surround an axis of the tubular housing


38




a


. Each clamp piece


38




b


is formed with a tapered inner surface which can mate the tapered end of the plunger


36




a


. The clamp pieces


38




b


are formed with an annular groove in which an O-ring


38




c


is received. The clamp pieces


38




b


are supported by supporting members


38




d


which surround a major portion of the plunger


36




a


. A circular cap


38




e


is put on the clamp pieces


38




b


. As shown, in use, a right tubular end of the blank


2


X is received in an annular clearance defined between the tubular housing


38




a


and a cylindrical unit consisting of the plunger


36




a


, the clamp pieces


38




b


, the supporting members


38




d


and the circular cap


38




e


. When, due to energization of the second hydraulic actuator


36


, the plunger


36




a


is shifted leftward (viz., in the direction of the arrow “M”) by a certain degree, the tapered end of the plunger


36




a


urge the clamp pieces


38




b


to move radially outwardly causing the O-ring to press the right tubular end of the blank


2


X against the tubular housing


38




a


. With this, the right tubular end of the blank


2


X is tightly clamped by the second clamp device


38


. It is to be noted that a left tubular end of the blank


2


X is clamped by the first clamp device


22


in substantially the same manner as that effected in the above-mentioned second clamp device


38


.




In the following, operation of the bellows producing device


50


will be described with reference to

FIGS. 2 and 3

.




First, by energizing the servo-motor


28


to rotate in one direction, the second clamp device


38


is moved away from the first clamp device


22


to a certain position. Then, the blank


2


X of the bellows


2


is set in the guide


24


having its left tubular end led into the annular clearance of the first clamp device


22


. Then, by energizing the servo-motor


28


to rotate in the other direction, the second clamp device


38


is moved toward the first clamp device


22


while receiving the right tubular end of the blank


2


X in the annular clearance thereof. When the left and right tubular ends of the blank


2


X are properly received in the respective annular clearances of the first and second clamp devices


22


and


38


, the servo-motor


28


is deenergized. Then, by energizing the ON/OFF valve of the fluid source


42


, pressurized fluid of the fluid source


42


is led to both the first and second hydraulic actuators


20


and


36


. With this, the respective plungers


20




a


and


36




a


are moved to actuate the clamp pieces


38




b


, and thus for the above-mentioned reasons, the left and right tubular ends of the blank


2


X are tightly clamped by the first and second clamp devices


22


and


38


. It is to be noted that under this condition, the blank


2


X has the axial length of “L” (see FIG.


1


).




Then, by energizing the servo-motor


28


, the second clamp device


38


is moved toward the fixed first clamp device


22


to compress the blank


2


X. When the blank


2


X is compressed to such a degree as to have the length of “L−a” (see FIG.


1


), the energization of the servo-motor


28


is reversed to expand the compressed blank


2


Y. When, due to the expansion, the blank


2


Y becomes to have the length of “L−a+b”, the servo-motor


28


is deenergized. Then, the ON/OFF valve is deenerigzed to release the right and left tubular ends of the expanded blank


2


Z from the first and second clamp devices


22


and


38


. Then, by energizing the servo-motor


28


, the second clamp device


38


is moved away from the first clamp device


22


to dismantle the blank


2


Z from the first and second clamp devices


22


and


38


.




The bellows


2


thus produced or reformed in the above-mentioned manner is used for assembling the flexible tube such as that shown in FIG.


6


.




It has been revealed that the bellows


2


produced in the above-mentioned manner has an excellent dimensional stability as compared with the bellows


102


(see

FIG. 5

) produced in the conventional manner. That is, even when the bellows


2


is practically used in the exhaust pipe line of the internal combustion engine as a part of the flexible tube, the entire length “Ls” is kept substantially unchanged irrespective of the temperature change of the exhaust pipe line. In fact, a very small shrinkage takes place in the bellows


2


. This may be caused from the residue of a stress of a type that causes the bellows


2


to contract in an axial direction when heated. It is however to be noted that the reduction in length of the bellows


2


means an increase in the certain length by which the bellows


2


can expand axially within the cover of the flexible tube. That is, the elongation flexibility of the bellows


2


is increased at the time when the flexible tube is practically used.




The entire contents of Japanese Patent Application P9-327735 (filed Nov. 28, 1997) are incorporated herein by reference.




Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the above teachings.



Claims
  • 1. A device for reforming a bellows for use in a heated atmosphere, said bellows being a metal pipe having a plurality of bulges formed therearound, said device comprising:a base member; a first clamp device fixedly mounted on said base member, said first clamp device having a first hydraulically actuated clamping means which clamps one tubular end of said bellows when actuated; a second clamp device movably mounted on said base member, said second clamp device having a second hydraulically actuated clamping means which clamps the other tubular end of said bellows when actuated; a hydraulic power source which hydraulically actuates said first and second hydraulically actuated clamping means when assuming ON condition; and an electric moving device which moves said second clamp device toward and away form said first clamp device when electrically energized, wherein each of said first and second hydraulically actuated clamping means comprises: a hydraulic actuator having an output plunger, said output plunger having a tapered leading end; a tubular housing in which said output plunger is axially movably received; a plurality of clamp pieces installed in said tubular housing in a manner to surround the tapered leading end of said output plunger, each clamp piece having a tapered inner surface which can mate the tapered end of said plunger; an O-ring received in an annular groove which is formed in the clamp pieces; supporting members installed in said tubular housing in a manner to surround a major portion of said output plunger, each supporting member supporting one end of the corresponding clamp piece; and a circular cap installed in said tubular housing and put on the clamp pieces.
  • 2. A device as claimed in claim 1, in which said electric moving device comprises:a slider on which said second clamp device is mounted to move therewith, said sliding having a threaded bore formed therethrough; a threaded shaft passing through said threaded bore of said slider while providing a meshed engagement therebetween; a supporting device for rotatably supporting said threaded shaft on said base member; and a servo-motor for rotating said threaded shaft when electrically energized.
  • 3. A device as claimed in claim 2, in which said supporting device holds a guide by which said bellows is held and guided.
Parent Case Info

This application is a divisional of Ser. No. 09/314,167 filed May 19, 1999, now U.S. Pat. No. 6,282,939.

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Entry
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