Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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_ACKGROUND 0~ INY~NTION
This invention relates generally to pressure switches, and more
particularly to a novel, improved pressure switch of simplified structure in
which a switch is operated by a shallow, dished shaped disc movable with snap
action between two positions of stability in response to predetermined pressures.
PRIOR ART
Snap disc-operated pressure-responsive switching devices are
known. An example of such device is illustrated and described in United States
Letters Patent Nos. 3,302,269, 3,365,557, 3,584,168, and 4,091,249. In such
devices, the snap disc itself usually defines a portion of a pressure chamber
so that fluid under pressure acts directly on the disc to cause it to snap
back and forth on reaching predetermined pressure conditions. In such devices,
it is necessary to establish a fluid seal between the housing and the disc to
prevent leakage. If the seal is produced by gripping the disc at its periphery,
the structure of the seal produces forces on the disc which tend to alter the
operating pressure or the disc. On the other hand, if the seal between the
disc and the housing is provided by a weld or the like, as illustrated in some
of the patents cited above, stresses tend to occur which, again, alter the
operating temperature of the disc. Consequently, in devices of the prior art
such as the device illustrated in such patents, it is generally necessary to
provide calibration means to pull in the disc or otherwise be certain that the
disc will operate at the desired operating pressures. Further, the cost of
accurately producing a weld to establish a seal between the housing and disc
is relatively high.
In other instances, a diaphragm is used in conjunction with a
snap disc wherein an actuator is positioned between the diaphragm and the disc
to transmit the pressure forces to the disc. In such devices, the calibration
pressures of the disc are altered by the actuator.
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SUMMARY OF THE INVENTION
In accordance w-lth the present invention, a novel and improved
snap disc~operated pressure swltch i9 provided having a simplified structure
wich provides operating accuracy and low manufacturing cost.
In accordance with one important aspect of this invention, a
nonmetallic, flexible diaphragm is positloned within a housing immedia~ely
against a shallow dish-shaped snap disc to seal the pressurP chamber of the
device while providing a force-transmitting medium which efficiently transmits
the pressure force directly to the disc without exposing the disc directly to
the pressure fluid. ~ith such structure, it is not necessary to produce a
seal between the dlsc per se and the housing even though the fluid under
pressure within the pressure chamber effectively acts directly upon the disc.
The elimination of the requirement for a direct fluid seal between the disc and
the housing improves operating accuracy by eliminating the application of
stress or forces to the disc other than the forces resulting from the fluid
under pressure. Consequently, the calibration of the disc established during
its manufacture is not altered by lts installation within the device.
In accordance with another important aspect of this invention,
the disc seat member is provided with a disc-supporting wall extending inwardly
from the seat which supports the disc against overstressing when high pressures
are encountered, Such element also provides a guide for the bumper which extends
between the disc and the switch.
In accordance with another important asepct of this invention,
a novel and improved switch system is provided to limit the stresses applied
to the movable contact support arm and to eliminate ~atigue failu~es when the
switch is operated through a large number of cycles.
In the illustrated embodiments, the diaphragm is formed of a
thin thermoplastic material, such as polyimide, marketed under the trade mark
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"Kapton." A peripheral seal is established between the diaphragm and the
housing assembly by a simple resilient gasket which may be formed, for example,
of neoprene or nitrile. Prefe~ably, a unitary element which provides the disc
seat also protects the disc from damage due to overpressure, provides the
switch bumper guide, and is formed with an amlular rib engaging the diaphragm
to ensure that localized high pressure is established between the diaphragm
and the neoprene seal member to prevent the possibility of leakage.
The housing assembly, including the switch housing and the
pressure chamber housing, is permanently connected by the simple expediency
of crimping the pressure chamber housing to the switch housing. Preferably,
the structure is arranged so that devices requiring relatively high operating
accuracy can be assembled and held together without crimping to allow testing
of the assembly to ensure that it meets specification requirements before the
assembly is completed by the crimping operation. In the event that a given
disc does not operate within the specification requirements for the device,
it is then an easy matter to disassemble the device and replace the disc with
another disc to provide the required operating accuracy.
In the embodiment arranged to limit stress on the movable
contact support arm, the arm is biased to a normally closed position. A spring-
biased operator is slidably mounted in the body and provides a central pro-
jection which extends through an opening in the contact arm. Such projection
engages the end of the bumper and a shoulder on the operator around such pro-
~ection is engaged by the arm on the side thereof remcte from the bumper. With
this structure, the maximum stress applied to the movable contact support arm
occurs when the contacts are open while the arm is functioning in a cantilever
manner and the arm is not overstressed under high pressure on the disc. In
fact, once the contacts close, overtravel of the disc merely causes separation
of the contact arm and the operator shoulder. Consequently, contact arm fatigue
failures are virtually eliminated.
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In accordance with another aspect of thls invention, two discs
can be mounted in ahutting relation.ship within the device to allow operation
at higher pressures.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevation in longitudinal section, illustrat-
ing the general structural arrangement of one preferred embodiment of this
invention;
Figure 2 is a cross section taken along 2-2 of Figure 1,
illustrating the mounting of the arm of the switch,
Figure 3 is a ragmentary section of the switch end of the
device, illustrating a simple structure for mounting the terminals of the
switch in the switch housing;
Figure 4 is a fragmentary end view of a valve operator which
is arranged to open a Schraeder valve or the like when the device is installed
in an operating system such as an automotive air condltioning system;
Figure 5 is a fragmentary, longitudinal section of a second
embodiment in which two discs are provided to allow efficient operation at
higher pressures;
Figure 6 is a longitudinal section of another embodiment
providing a modified switch arrangement; and
Figure 7 is an exploded, perspective view of portions of the
switch of the embodiment of Figure 6.
DETAILED DESC~IPTION OF THE DRAWINGS
The one illustrated pressure switch, in accordance with the
present invention (illustrated in Figures 1 to 5), is partlcularly suited for
use in automotive air conditioning systems wherein it is threaded onto a
Schraeder-type valve. The housing assembly includes a threaded fitting portion
10 providing internal threads 11 which thread onto the Schraeder valve when the
device is installed. During installation, a valve operator 12 engages the valve
stem of the Schraeder valve and opens the ~alve so that fluid communication
is provided with the associated system. When the device is removed for replace-
ment or the like, the Schraeder valve automatically closes to seal the system.
Welded to the fltt~ng portion 10 is a sheet metal housing 13
having an axially extending wall 14 which fits around a flange 16 and a switch
housing member 17 and is crimped at 18 to permanently connect the housing
members together. As an alternative, the fitting portion 10 and housing 13
can be formed as a unitary element, for example, as a screw machine part.
The housing 13 and switch housing 17 cooperate to define a
cavity divided into a pressure chamber 19 and a switch chamber 21 by a flexible
diaphragm 22 formed of a nor~etallic material such as a polyimide marketed under
the trade nark "Kapton" by E. I. DuPont de Nemours & Company. A peripheral
seal is provided between the diaphragm 22 and the housing 13 by a gasket 23,
preferably formed of neoprene or nitrile or the like, which is compressed
between a radial flange 24 on the housing and one surface of the diaphragm by
a flange 26 of a disc seat member 27. The flange 26 of the dlsc member 27 is
held against the side of the diaphragm 22 opposite the gasket 23 by the flange
16, which is held by the crimping of the housing 13. Preferably, the flange
26 is formed with an annular rib 28, which produces an annular zone of high
compression to ensure that leakage does not occur between the diaphragm and
the gasket.
The disc seat member is provided with a radially inward extend-
irlg wall 29 having a forward face 31 spaced bsck from the forward face of the
flange 26 to provide a disc seat 32 in which a shallow dished shape snap disc
33 is positioned. The snap disc 33 is shaped to provide two positions of
stability between which it moves with snap action in response to predetermined
pressures in the pressure chamber 19.
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In the position illustrated in ~igure 1, the dlsc ls arched
toward the chamber 19 and i5 seated at its periphery in the disc seat 32.
The diaphragm engages the disc and transmits fluld forces from the chamber 19
to the disc so that when sufficient pressure is developed in the chamber 19,
the disc is caused to snap thsough to its opposite position of stability, in
which it extends substantially along the forward face 31 of the disc seat
member 27. In order to ensure that the forward face 31 does not interfere with
such snap movement to the opposite position of stability, it is inclined back
from the plane of the disc seat to allow the snap disc 33 to snap through to
its opposite position of stability. However, such face 31 is positioned against
or adjacent to the disc after it snaps through to support the disc and prevent
it from being damaged if overpressure occurs in the pressure chamber 19.
Because the forward face 31 is inclined back from the plane of
the edge of the disc 33 the disc is supported only at its edge in both positions
of stability. This insures that the effective area of the disc does not change
when it snaps back and forth. If fos example the disc seat were flat the disc
would be supported on its edge in one position and would be supported on the
inner edge of the seat in its other position. In such structure, the effective
area of the disc against which the pressure would react would not be the same
in both positions. However, an inclined seat, having an angle of inclination
greater than the disc curvature at its edge, eliminates such effective area
change because the disc is supported at its edge in both positions.
The disc seat member 27 is also provided with a central tubular
portion 34 to guide a cylindrical bumper 36, which extends between the disc 33
and a movable contact arm 37 for the operation of the switch.
The switch includes a first terminal 38 which extends through
an opening 39 in the switch housing 17 and provides a lateral portion 41 on
which one end of the movable contact arm 37 is mounted. A stationary contact is
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provided by a second terminal member 42, which extends through an opening 43 in
the housing 17 and is also provided with a lateral portion 44 providing a layer
of contact material 46 which functions as the stationary contact. A movable
contact 47 is mounted on the ree end of the arm 37 and is moved into and out
of engagement with the fixed contact 46 by the bumper 36 when the snap disc 33
snaps between its two positions of stability.
Figure 3 illustrates the manner in which the two terminals 38
and 42 are permanently mounted in the switch housing. After the terminals are
- positioned in their respective openings, they are staked, as illustrated at
48 and 49, so that they are permanently mounted in position. Preferably, the
switch housing 17, the disc seat member 27 and the bumper 36 are molded from
a nonconductive plastlc material so that separate insulating structure is not
required,
The ~alve operator 12 may also be molded of plastic material
and, as best illustrated in Figures 1 and 4, is formed with axial grooves 51
and 52 which provide communication between the threaded passage in the fitting
portion 10 and the pressure chamber 19. The grooves 51 provide saw tooth
shaped ridges to allow it to be press-fitted into position.
As best illustrated in Flgure 2, the movable contact arm is
mounted on the lateral portion 41 of the terminal 38 by a spot weld at 50, and
is formed with a semicircular cutout 53 so as to provide a bend line sub-
stantially at 54. With such structure, the welding operation does not signi-
ficantly affect the spring force of the movable contact arm, and the arm bends
along a bend line substantially adjacent to the side of the switch chamber so
that the effective length of the arm in its movement is maximi~ed.
The snap disc 33 is shaped during its manufacture so that it
operates at substantially the desired pressures of the de~ice. Since the disc
is not subjected to any clamping or welding stresses when installed, it acts
substantially as a free disc and operates at the calibratlon pressures determined
during its manufacture. The engagement of the face of the disc by the diaphragm
22 does not apply any significant forces to the disc, other than the pressure-
induced forces. Consequently, the calibration pressures of the free disc are
substantially unaltered by the diaphragm during the assembly of the disc in the
device. Further, the diaphragm engages the periphery of the disc and maintains
the disc in its seat.
In the illustrated device, the disc may, for example, be cali-
brated during its manufacture to snap from the illustrated position of stability
through to its opposite position of stability whenever the pressure within the
pressure chamber 19 reaches 45 psi. During its snap movement from the illu-
strated position to its opposite position of stability, the bumper 36 moves to
the left, as viewed in Figure 1, and causes the movable contact arm 37 to carry
the movable contact into engagement with the fixed contact 46 closing the switch.
The disc then remains in such position until the pressure in the chamber 19
drops below the lower calibration pressure, which for example may be 24 psi.
Upon reaching the lower operating pressure, the disc snaps back through to the
illustrated position, allowing the switch to open.
In accordance with the present invention, the disc calibration
pressures are not materially altered by the mounting of the disc, and it is
only necessary to manufacture the disc so that when the spring force of the
movable arm is applied to the disc in the assembled device, the actual operat
ing pressures of the disc are within the specification requirements of the
device.
In the illustrated device, the spring force applied to the disc
by the bumper 36 tends to bias the disc toward the illustrated position. Con-
sequently, the disc is manufactured in the above example where it operates at
45 psi and 24 psi, so that in its free, unbiased state, the disc would snap
through at a pressure slightly g~eater than 45 psi in one dlrection and at a
pressure slightly greater than 24 psi in the opposite direction. The amount of
change of the calibration pressure caused by the spring bias of the movable
contact arm is substantially known and does not vary significantly from one
device to the next, 50 compensation for such force can be uniformly accomplished
during the manufacture of the device. On the other hand, in prior art systems
where the clamping forces on the disc or stresses produced during welding affect
the operating temperature of the disc, it is difficult to provide a uniform
variation of the calibration pressures.
With the illustrated structure, the diaphragm fits against the
entire disc and is sufficiently elastic and flexible to move with the disc with-
out inducing forces other than pressure forces. Although a Kapton diaphragm is
illustrated, other suitable materials such as rubber may be used. If a rubber
diaphragm is used, the separate gasket may not be required. The diaphragm, in
addition, functions to keep the disc from bounclng when it operates so the
tendency for calibration drift to occur during the use of the device is sub-
stantially eliminated.
Further, in the present structure in which the disc is freely
positioned and is not permanently mounted by welds or the like, it is possible
to assemble the entire unit and clamp the housing together without crimping
while the unit is tested for operating accuracy. If the unit does not operate
under such conditions within the proper pressure ranges, the unit can be dis-
assembled and the disc removed for replacement by another disc for retesting.
Once the testing is satisfactorily accomplished, the housing 13 can then be
crimped to complete the device. This testing before final assembly can be
accomplished with the present invention, since the degree of clamping of the
diaphragm does not in any way affect the operating pressure of the disc. Any
difference in clamping is taken up solely in the gasket 23. In units in which
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a higher degree of clamping is provlded the gasket is compre~sed to a greater
degree but the relative positions of the switch, disc and diaphragm are not
altered. Therefore, the degree of clamping has no effect on the operation
of the device.
Figure 5 illustrates the second embodiment of this invention,
which is preferably used when the device must operate at higher pressures.
The pressure at which a snap disc operates depends upon the properties and
thickness of the material, and depends also on the amount of curvature formed
in the disc during its manufacture. Because the disc in the ~resent invention
is acted upon along its entire surface, dificulty can be encountered in
producing discs calibrated for relatively high pressures, for examples pressures
on the order of 90 psi. If the disc is manufactured of material which is too
thick, or if too much curvature is required, difficulty is encountered in
obtaining calibration accuracy and the disc tends to be incapable of repeated
cycling through a large number of cyclic operations. In order to overcome such
difficulty, a structure as illustrated in Figure 5 is used in which two discs
are positioned immediately ad~acent to each other, instead of a single disc as
illustrated in the embodiment of Figure 1.
Preferably, such discs are substantially identical, and are
formed of the sc~me material and provided with the same curvature. If, for
example, the device is intended to operate in one direction at 90 psi, and in
the other direction at 48 psi, two discs preferably each having calibration
pressures of substantially 45 psi and 24 psi are used. In this embodiment,
the disc 33a is positioned against the disc seat 32 and the second disc 33b is
positioned between the disc 33a and the dlaphragm 22. Here again, the discs
operate the switch through a bumper 36 in the same manner as described above in
connection with the first embodiment. The structure of the overall device is
essentially the same as in the first embodiment, except that the depth of the
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disc seat 32 in this embodi~ent i6 appropriately increased so that there is
sufficient room to accommodate the additional thickness of the two discs.
If necessary, a thin film of material such as Teflon*(not
illustrated) can be positioned between the two discs to reduce any frictional
contac~ therebetween to provide greater operating accuracy. Also in this
embodiment the two discs can be selectively assembled for greater operating
accuracy. For example, in the manufacture of discs, some discs have a cali-
bration pressure on the lower side of acceptable tolerance and other discs
operate on the high side of the tolerance, even though the discs are sub-
stantially identical within the range of possible manufacturing accuracy. Insuch instance, a disc on the low die of the tolerance is assembled with the
disc on the high side of the tolerance to produce an assembly which operates
essentially in ~he middle of the tolerance range. In practice, the assembled
discs operate at a pressure which is substantially equal to the sum of the
calibration pressures of the individual discs.
With this embodiment, the disc can be manufactured of thinner
material or with lower curvatures so that the discs are capable of extended
operation without failure, while providing a relatively high operating pressure.
Figures 6 and 7 illustrate an embodiment in which overpressure
conditions cannot produce overstressing of the movable contact support arm.
In this embodiment, the housing assembly includes a switch housing 61, a seat
member 62, and a fitting postion 63, all of which are molded from plastic
material, such as a phenolic resin. The fittlng portion 63 is formed with a
radial shoulder 64, which is opposed to a radial shoulder 66 ~ormed on the
switch housing 61, and a crimp ring 67 secures the parts together by embracing
the opposed shoulders 64 and 66.
Here again, the fitting portion 63 is formed with a threaded
opening 68, allowing the device to be threaded onto a Schraeder valve. In this
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embodiment, however, an integral p~o~ection 69 is molded into ~he fitting portion
to open the Schraeder valve when the device is threaded into place. A plurality
of axial passages 71 provide fluid communication through to the disc chamber 72
formed between the end face of the fittlng portion 63 and the seat member 62.
Such fitting portion may be machined from metal or be molded as illustrated.
Here again in this em~odiment a snap disc 73 ls held in an
inclined seat formed in the seat member 62. The inclination of the seat insures
that the disc is supported by its edge in both positions. In this particular
embodiment, the seat member 62 is not formed with a forward face intended to
fit the contour of the disc after the disc is snapped through, but instead is
shaped to support the disc only substantially adjacent to its center after the
disc is operated. A diaphragm 74 is again positioned against the disc in the
same manner as the first embodiment, and a seal is provided by the gasket 76.
Positioned within a switch chamber 77 defined by the switch
housing 61 and the seat member 62 is a switch consisting of a pair of terminals
78 and 79. A movable contact arm 81 shaped as best illustrated in Figure 7 is
riveted at 80 to the inner end of the terminal 78. Mounted on the free end of
the movable contact arm is a movable contact 82 which moves into and out of
engagement with a fixed contact 83 provided on the inner end of the terminal 79.
In this instance, however, the movable contact arm 81 is biased toward the
closed position and is moved to its open posltion by an operator 84 in response
to disc movement. The operator 84 is slidably mounted in the switch housing
and is provided with a shoulder 86 guided within a first axial passage 87 and a
reduced diameter guide projection 88 which is guided in a reduced diameter axial
passage 89. A coil-type compression spring 91 engages the shoulder on the
switch housing 61 at one end and the shoulder 86 at its other end and resiliently
urges the operator 84 to the right, ~s viewed in Figure 6.
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The operator is provided wlth a reduced diameter pro~ection 92,
best illustrated in Figure 7, which extends through an opening 93 in the movable
contact arm 81 with clearance and engages the end of a cylindrical bumper 94.
The bumper extends from the projection 92 to the disc 73 and transmits disc
movement to the operator and, in turn, the movable contact arm 81. Such
movable contact arm 81 is formed with a pair of projections 95 on opposite
sides of the opening 93 which engage the face 96 of the shoulder 86 on the
operator 84.
The force of the spring 91 is selected so that it is sufficient
to overcome the spring action of the movable contact arm and to move the movable
contact arm to the switch-open position illustrated in Figure 6 when the disc
73 snaps through to its low pressure position.
The structure of thls embodiment ensures that the movable
contact support arm 81 is not overstressed under overpressure conditions, since
the movement of the disc beyond the switch-closed position does not produce
additional stress in the contact arm, but merely moves the operator away from
the contact arm. Thereore, high stresses do not occur in the arm by bending
it after the contacts are closed. In effect, the maximum stress that can be
applied to the movable contact arm 81 is determined by the available force in
the spring 91 and the position to which the disc 73 moves when the pressure
drops. Actual tests have established that this structure virtually eliminates
fatigue failures in the movable contact arm, even when the switch is operated
through extremely large numbers of cycles. Switches of the type illustrated
in the first embodiment often fail under life testing to 100,000 operating
cycles. However, switch structures in accordance with the embodiment of
Figures 6 and 7 regularly pass life testlng of 200,000 or more cycles.
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Although prefer~ed embodimentfi o~ thie inventlon are illustrated,
it should be understood that various modifications and rearrangements of parts
~ay be resorted to without departlng from the scope of the invention disclosed
and clai~ed herein.
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