Bellows assembly and method of making the same

A bellows assembly and method of making the assembly are disclosed. The assembly comprises a bellows head including thin walled flexible members which are joined to define an expansible chamber. An anchor fitting attaches and communicates the bellows head to a capillary tube and an expansible fluid occupies the tube and chamber. A base supports the bellows head and capillary tube with the anchor fitting interconnecting the bellows head, tube and base. The anchor fitting is bonded to the diaphragm member and capillary tube and deformably engages the base plate to clamp the base plate to the bellows head.

BACKGROUND OF THE INVENTION 
The present invention relates to fluid operated actuators and more 
particularly relates to expansible chamber bellows assemblies. 
FIELD OF THE INVENTION 
Thermostatic and pressure controls have employed thin walled metal bellows 
for operating actuated devices such as control switches, valves and the 
like. The bellows are typically filled with a fluid and are flexed in 
accordance with differential pressure forces acting on the bellows walls. 
One typical use of such bellows is in thermally responsive controls 
wherein the expansible chamber defined by the bellows communicates with a 
closed capillary tube and a vaporizable liquid is contained by the tube 
and bellows. An increase in temperature at a location along the length of 
the capillary tube causes an increase in vapor pressure and the bellows 
chamber expands while a reduction in temperature at a location along the 
length of the capillary tube permits contraction of the bellows volume. 
Expansion and contraction of the bellows actuates a switch or valve 
directly or through a suitable motion transmitting linkage. 
In order for such controls to respond accurately and consistently to sensed 
pressure or temperature changes the bellows assembly must positively 
engage and remain accurately positioned with respect to the actuated 
device. Accordingly, bellows heads have conventionally included 
structurally strong, rigid fittings for both anchoring the bellows head in 
place with respect to the associated control and for transmitting force 
from the bellows head to the switch, valve, or motion transmitting 
linkage. At the same time the bellows chamber must be constructed from 
easily flexible components in order for the control to be adequately 
sensitive to pressure or temperature changes. 
One successful prior art bellows head included a pair of flexible sheet 
metal diaphragms hermetically brazed together at their outer peripheries, 
each having a central opening in which respective force transmitting and 
anchoring fittings were mounted. The fittings were attached to the 
respective diaphragm members by brazed joints. The anchor fitting was 
constructed to be secured to a rigid base plate by a staking operation. 
The base plate was in turn rigidly attached to the control housing. 
The fittings were machined from rod stock (frequently brass) and the 
brazing operation was usually accomplished by fixturing all of the 
components of the bellows head together and passing them through a brazing 
furnace, or the like, in order to bond the assembly components together. 
The production costs of these bellows heads were relatively high for a 
number of reasons in addition to those attributable to costs of materials. 
The number of brazed joints between components of the assemblies was 
relatively great which tended to increase the chances for "leaky" 
malfunctioning bellows being productd. Because the anchor fitting had to 
be seated in an opening in the associated diaphragm member the diaphragm 
members of each bellows had to be separately stocked and handled during 
production. Because the diaphragm members were formed from thin sheets of 
metal, any operation which would tend to alter the stress conditions of 
the diaphragm material would also tend to change the diaphragm spring rate 
and thereby alter the response of the diaphragm to sensed temperature or 
pressure changes. The stamping operation for producing the diaphragm 
member openings was such an operation. 
SUMMARY OF THE INVENTION 
The present invention provides a new and improved bellows assembly and 
method of making the same wherein the bellows assembly construction is 
substantially simplified and the cost of its manufacture reduced 
appreciably compared to the prior art. 
A bellows assembly constructed according to the invention includes a 
supporting base member by which the assembly is anchored to a control 
unit, a bellows head and a capillary tube. The bellows head includes an 
anchor fitting by which the bellows head and capillary tube are attached 
and which fixedly anchors the bellows head to the base member. The anchor 
fitting is formed from light gage sheet metal having a tubular body 
section and an outwardly extending peripheral flange at one end which is 
hermetically bonded to the bellows. The body section projects through a 
base member opening for receiving the capillary tube which is hermetically 
bonded in the fitting body. The fitting body both receives the capillary 
tube and anchors the bellows head to the base member. 
The base is firmly clamped between the fitting flange and the crimped 
fitting body portion. The fitting body section is preferably outwardly 
upset and crimped, with the crimped portion forced into engagement with 
the base plate. The anchor fitting thus serves to attach the bellows head 
to the base member as well as to accurately locate the bellows head with 
respect to the base. 
In a preferred embodiment of the invention the fitting flange is resistance 
welded to its associated bellows diaphragm so that the confronting bellows 
diaphragm and fitting flange have a weld joint extending continuously 
about the fitting body opening. With the diaphragm member so attached to 
the anchor fitting the portion of the diaphragm extending across the 
fitting opening is supported and isolated from stress patterns in the 
remainder of the diaphragm member, and vice versa. Accordingly a simple 
piercing tool can be thrust through the diaphragm member into the tubular 
fitting body section without any danger of bending or excessive tearing of 
the diaphragm member radially beyond the weld joint. Moreover the piercing 
can be accomplished without materially changing the stress conditions of 
the diaphragm portion radially outwardly from the flange, i.e. the "spring 
rate" of the diaphragm is unaffected. 
This feature of the invention permits use of identical diaphragm members 
adjacent the base plate and at the extension side of the bellows head by 
eliminating the need for producing the bellows chamber opening by a 
stamping operation as well as eliminating tooling associated with the 
stamping operation. Any necessity for separately producing, handling and 
stocking bellows diaphragm members which differ from each other only by 
virtue of having a stamped bellows chamber opening is also precluded. 
Other features and advantages of the invention will become apparent from 
the following detailed description of a preferred embodiment made with 
reference to the accompanying drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 of the drawings schematically illustrates a control unit 10 
embodying the present invention connected for controlling operation of a 
suitable control device 11 in response to sensed temperature. The control 
unit 10 comprises a control housing, or frame, 12 which rigidly supports a 
control switch 13 and bellows assembly 14, the latter being effective to 
operate the control switch via an actuating linkage 15 (schematically 
illustrated). The controlled device can be formed by any suitable 
electrically operated component and for the purpose of this description 
may be considered to be an electric motor for driving a refrigerant 
compressor drive motor which is energized by the control unit 10 in 
response to a given sensed temperature level and de-energized in response 
to the control unit sensing a predetermined lower temperature. 
The bellows assembly 14 is formed by a bellows head 16, a capillary tube 18 
(attached to and communicating with the bellows head), and a supporting 
base member 20 supporting the bellows head and capillary tube and rigidly 
supported by the control unit housing 12. The bellows head 16 is 
preferably a capsule type bellows which expands in response to increases 
in sensed temperature along the length of the capillary tube and contracts 
when the temperature along the capillary tube is reduced. Expansion and 
contraction of the bellows head actuates the control switch 13 via the 
linkage 15 to control energization of the device 11. The locations of the 
control switch and bellows assembly relative to the control housing 12 are 
accurately established and maintained and together with the geometry of 
the linkage 15 govern the temperature levels at which the device 11 is 
energized and de-energized. 
The bellows head 16 is formed by thin resilient sheet metal diaphragm 
members 24, 26, an extension point fitting 28 carried by the diaphragm 
member 24 for engagement with the actuating linkage 15, and an anchor 
fitting 30 for attaching the diaphragm member 26 to the base member 20 and 
the capillary tube 18. The diaphragm members 24, 26 are substantially the 
same, each being formed by a circular body having a central generally 
circular, planar section 34, a series of circumferential corrugations 
extending about the central body section 34 and a outwardly extending 
peripheral flange 38. The diaphragm flanges 38 are bonded together by a 
weld bead 40 which extends continuously about the members to establish a 
hermetic chamber 42 within the bellows head. The chamber 42 is 
communicable with the capillary tube 18 via a central opening 44 which is 
formed in the diaphragm member 26. In the preferred embodiment the 
diaphragm members are formed from stainless steel sheet material which is 
only a few thousandths of an inch thick. 
The capillary 18 is a relatively thin walled copper alloy tube having an 
open end section 50 received by the anchor fitting, a remote hermetically 
closed end 52 and a body section 54 which is illustrated in broken lines 
as forming a helix. The chamber 42 and capillary tube 18 contain a 
vaporizable fluid of any suitable or conventional type which causes 
expansion of the bellows head in response to sensed temperature increases 
along the extent of the capillary and contraction of the bellows head when 
temperatures along the capillary are reduced. 
The extension point fitting 28 is formed from a drawn cup-like sheet steel 
member which is inverted on the diaphragm member 24 and has a planar end 
surface 28a engaging the linkage 15 and a circumferential flange 28b by 
which the extension point fitting is bonded to the diaphragm member 
central section 34. In the preferred and illustrated embodiment of the 
invention the diaphragm member 24 and extension point fitting 28 are 
connected by a resistance welded joint and the diaphragm member central 
section 34 is imperforate. 
The anchor fitting 30 is formed by an open ended drawn sheet steel member 
which defines a thin walled tubular body 45 extending from the diaphragm 
member 26 through the supporting base 20 and a circumferential generally 
planar flange 46 by which the anchor fitting 30 is attached to the 
diaphragm member central section. The anchor fitting 30 defines a through 
opening 47 communicating with the central diaphragm opening 44, an 
outwardly bulged crimp 48 in the body 45 for rigidly clamping the 
supporting base member and bellows head together, and a flared end section 
49 through which the capillary tube is received. 
The base member 20 is formed by a stamped structurally strong sheet metal 
plate defining a central generally circular land 60 supporting the bellows 
head 16 and a mounting opening 62 through which the anchor fitting 30 
extends. In the preferred embodiment the mounting opening 62 is 
non-circular, or polygonal, and defines relieved sections 64 which coact 
with the anchor fitting body to effectively key the anchor fitting to the 
base member and prevent rotation of the bellows head relative to the 
linkage 15 and the control body. 
FIG. 2 shows, in abbreviated schematic form, a procedure by which the 
bellows assembly 14 is fabricated. The bellows head is assembled in a 
series of operations followed by assembly of the bellows head 16, 
capillary tube 18 and the supporting base 20. 
The bellows head 16 is assembled by welding the diaphragm members to the 
respective extension point and anchor fittings and then to each other. 
After the extension point and anchor fittings are initially drawn they are 
copper plated and fed to nests which receive and support the respective 
fittings and diaphragm members during their joining. Referring to FIG. 3 a 
nest 70 (illustrated in part) supports an anchor fitting 30 with its 
flange 46 oriented upwardly and its body 45 extending downwardly through a 
centering opening in the nest. A diaphragm member 26 is disposed in the 
nest over the fitting 30 with the nest 70 engaging the diaphragm about its 
periphery to center it with respect to the fitting. 
The fitting and diaphragm are resistance welded together in the next 70 at 
a welding station illustrated schematically by FIG. 3. The flange 46 is 
formed with a narrow continuous circumferentially extending bead 46a 
contacting the diaphragm 26. A resistance welding power supply 72 is 
connected across the fitting 30 and diaphragm 26. When welding current 
flows through the juncture of the bead 46a and the diaphragm the fitting 
and diaphragm materials are rapidly fused together continuously about the 
flange 46 so that the anchor fitting and diaphragm are hermetically 
joined. 
The resistance welding equipment is schematically illustrated and may be of 
any suitable type. The welding equipment is preferably constructed so that 
one welding electrode is reciprocally movable into welding position (as 
illustrated) when the nest 70 is moved to the welding station. After the 
weld is formed the electrode is withdrawn to enable the nest to move to 
another work station. 
Assembly of the extension point fitting 28 to the diaphragm 24 is 
accomplished substantially the same as described in reference to FIG. 3 
and therefore is not further illustrated or described. 
When the diaphragm 26 and anchor fitting 30 are joined, the nest 70 is 
advanced to a piercing station where the aperture 44 is formed. Referring 
to FIG. 4 the nest 70 is located in the piercing station so that a 
piercing tool 80 is aligned with the anchor fitting through the opening 
47. The preferred piercing tool 80 is a cylindrical rod having a 
circularly tapered end forming a sharp point. The tool 80 is advanced into 
the diaphragm central section where it easily pierces the diaphragm 
material. When the tool 80 is withdrawn a pentagonal aperture remains in 
the diaphragm (See FIG. 5). 
Because the diaphragm is welded to the anchor fitting about the flange 46 
the piercing operation does not affect the stress in the diaphragm 
radially beyond the anchor fitting flange 46. Accordingly the formation of 
the aperture 44 in the diaphragm member 26 does not alter the spring rate 
of the diaphragm. Moreover the polygonal shape of the aperture 44 serves 
to prevent the capillary tube end 50 from extending into the chamber 42. 
The bellows head assembly is completed by hermetically joining the 
diaphragm members along their peripheral flanges 38. Referring now to FIG. 
6 the welded diaphragms and fittings are separately transported to a laser 
beam welding apparatus where they are situated in mating nests 82, 84 and 
welded together by use of a laser 86. The nest are constructed from a 
metal which is an efficient heat conductor have circumferential projecting 
rims between which the diaphragm flanges 38 are clamped and are rotatable. 
The nests are rotatably driven by a suitable drive mechanism to rotate the 
engaged diaphragms relative to the laser beam. The engaged flanges 38 are 
thus moved through the laser beam which melts and fuses the diaphragm 
flanges. The heat conductive nest material carries heat away from the weld 
joint to chill it. After slightly more than 360 degrees of rotation the 
laser beam is discontinued and the welded bellows head is removed from the 
nests 82, 84. 
The assembled bellows head is then attached to the supporting base member 
20. In accordance with the present invention and as illustrated by FIGS. 7 
and 8 the bellows head assembly is placed in a supporting nest 90 (only a 
part of which is shown) with the anchor fitting body 45 extending 
upwardly. The base member is disposed on the bellows head assembly with 
the anchor fitting body extending loosely through the base member mounting 
opening 62. The nest 90 is moved to a work station illustrated in FIGS. 7 
and 8 at which the anchor body is upset by a forming tool 92 to clamp the 
base member and bellows assembly together. The tool 92 defines a 
cylindrical cavity 94 conforming to the cylindrical shape of the 
undeformed fitting body 45. The cavity 94 defines an internal end face 94a 
which engages the projecting end of the fitting body as the tool advances 
and an external annular end face 96 surrounding the cavity 94 for crimping 
the fitting body against the base member. 
As the tool 92 advances, the projecting end of the anchor fitting body is 
closely surrounded and supported by the tool cavity wall 94. When the end 
face 94a engages the projecting end of the anchor fitting body the anchor 
fitting body section between the tool 92 and the base member bulges 
outwardly as illustrated by the broken lines in FIG. 7. The outwardly 
bulging body section expands into the supporting base opening 62. Part of 
the bulged section expands into the relieved opening sections 64 so that 
the support base and bellows head assembly are fixed against relative 
rotation by the key-like interengagement between anchor fitting and 
supporting base. 
As the tool 92 continues to advance toward the support base its external 
end face 96 engages the bulged section of the anchor fitting body and 
crimps the bulged section against the support base (See FIG. 8). The 
compressive force exerted by the tool 92 on the bellows head assembly 
assures that the central sections of the bellows diaphragms are engaged 
with each other due to flexure of the diaphragm members and therefore that 
the anchor fitting flange 46 is urged against the support base. Thus, when 
the bulged section of the body 15 is crimped, as illustrated by FIG. 8, 
the support base is tightly clamped between the crimped fitting body 
section and the flange 46. The clamping between the fitting body and the 
base member fixes the spatial relationship between these components so 
that when the base is fixed to the control body the control will be 
readily calibrated and operate reliably. 
The bellows assembly undergoes additional forming operations preparatory to 
the capillary tube being attached. The nest 90 is moved to a work station 
at which the anchor fitting body projecting end is necked down to produce 
an inside diameter just slightly greater than the capillary tube diameter 
(See FIG. 9). This operation is accomplished with a suitably tool 100 
which is forced onto the fitting body to deform it and then retracted. 
At a succeeding work station the projecting tip end of the fitting body is 
flared radially outwardly by a male tool 102 which is thrust into the 
fitting body. 
The capillary tubing is then inserted into the anchor fitting body and a 
suitable brazing material is placed in the flared fitting body end. The 
capillary tube end 50 engages the diaphragm member 26 preventing the tube 
end from entering the chamber 42. 
The capillary tube brazing material and anchor fitting are subjected to a 
source of high temperature flame, or a high temperature furnace 
atmosphere, which melts the brazing material to hermetically bond the 
capillary tube to the anchor fitting. 
The temperature responsive fluid is then introduced into the capillary tube 
and chamber 42 after which the capillary tube end 52 is sealed closed. 
As indicated previously, the bellows assembly is fixed to the control unit 
housing 12 so that the bellows head support location is rigidly fixed. The 
supporting base is generally fixed to the housing by a staking operation 
after which the control is calibrated. 
While only a single embodiment of the invention is illustrated and 
described in detail the present invention is not to be considered limited 
to the precise construction and methods of construction disclosed. Various 
modifications, adaptations and uses of the invention will become apparent 
to those skilled in the fields to which the invention relates and the 
intention is to cover all such modifications, adaptations and uses which 
come within the scope or spirit of the attached claims.